Patent Description:
The present invention generally relates to the synthesis and processing of nanostructures, composite materials comprising nanostructures, and in particular to a method of forming a composite article comprising substantially aligned nanostructures.

Composites are heterogeneous structures comprising two or more components, the combination taking advantage of the individual properties of each component as well as synergistic effects if relevant. Advanced composites refer to a class of materials in which engineered (e.g., man-made) fibers are embedded in a matrix, typically with the fibers being aligned or even woven such that a material with directional (anisotropic) properties is formed. A common example of an advanced composite is graphite-epoxy (Gr/Ep) wherein continuous aligned carbon fibers (stiff/strong/light) are embedded in a polymer (epoxy) matrix. Materials such as these have been used in the Stealth Bomber and Fighter and in sporting equipment, among other applications. Advanced composite systems comprising multiple materials can also be useful in applications where performance benefits from weight savings. Combining carbon nanotubes (CNTs) with other materials, including macro- advanced composites, can create yet new materials with enhanced physical properties, particularly enhanced engineering properties. Specifically, CNTs have been studied and applied widely as reinforcements for polymers. CNTs have been shown to exhibit strong adhesion to several polymers, for example, where individual CNTs are embedded in and then pulled out of a thermoplastic. While the use of CNTs in composite materials has been studied, existing CNT processing techniques often display several drawbacks. For example, the syntheses of CNTs often result in structures having large diameter and insufficient length, which often results in poor alignment of the CNT axes. Also, dispersion of the CNTs in secondary materials, which typically requires uniform wetting of the CNTs by the secondary materials, is often hindered by CNT agglomeration. Last, alignment of CNTs in the secondary materials may be difficult to achieve in general, particularly when alignment of nanotubes is desired in a system comprising large (e.g., orders of micron diameter) advanced fibers, a secondary material (matrix), and well- aligned CNTs in the secondary material. There are numerous examples of composites comprised of disordered arrangements and/or low volume fractions of CNTs, which exhibit one or more of these drawbacks.

<CIT> discloses, in its own words, nano-composite materials with enhanced thermal performance that can be used for thermal management in a wide range of applications. According to this reference, one type of nano-composite material has a base material and nanostructures (e.g. nanotubes) dispersed in the base material, and another type of nano-composite material has layers of a base material with nanotube films disposed thereon.

<CIT> discloses, in its own words, a fiber velvet comprising nano-size fibers or nanofibrils attached to micro-size fibers. Methods of manufacturing the velvet as well as various uses of the velvet are also described, according to this reference.

<CIT> discloses, in its own words, a thermal interface material including a macromolecular material and a plurality of carbon nanotubes embedded in the macromolecular material uniformly. The thermal interface material includes, according to this reference, a first surface and an opposite second surface. According to this reference, each carbon nanotube is open at both ends thereof, and extends from the first surface to the second surface of the thermal interface material.

<CIT> relates, in its own words, to a structure of and a process of forming an integrated circuit package that uses the thermal interface material layer having an aligned array of carbon nanotubes affixed to a surface of the layer.

<CIT> discloses, in its own words, a composite material and its production method. According to this reference, the composite material comprises at least one kind of material selected from carbon fibers and carbon nanotubes, having the fibers sandwiched by metal layers at least comprising aluminium to compose a composite sheet.

<CIT> discloses, in its own words, a composite and a process for forming it, said process comprising providing a substrate bearing crystalline and preferably single crystal filaments as growths on the substrate and forming a solid matrix encompassing the filaments.

<CIT> discloses, in its own words, a composite material manufacturing process and resulting structure including high strength material whiskers having a characteristic orientation when placed in an electromagnetic field. In one example, according to this reference, whiskers are disposed between lamina and oriented generally perpendicular to the fiber layers. The whisker orientation is, according to this reference, maintained during a curing cycle for the respective matrices wherein the matrix viscosity allows the whiskers to orient in response to the applied electromagnetic field. The whiskers, according to this reference, retain their orientation in the resulting laminate to provide improved structural integrity for the laminate.

<NPL> discloses, in its own words, a review of the progress in the field of mechanical reinforcement of polymers using nanotubes. Initially, the basics of fiber reinforced composites are introduced and the prerequisites for successful reinforcement discussed. The effectiveness of different processing methods is compared and the knowledge of the art known to the authors of the document and of its publication date demonstrated. In addition, levels of reinforcement that have actually been achieved are discussed.

<NPL> discloses, in its own words, the use of inter-laminar carbon-nanotube forests to fasten adjacent plies in a 3D composite material, thereby to provide enhanced multi-functional properties along the thickness direction. In particular, according to this reference, multi-walled carbon nanotubes are grown on micro-fibre fabric cloths which are used as building blocks.

Accordingly, improved materials and methods are needed.

The presently claimed invention provides a method of forming a composite article, as recited in claim <NUM> below.

The presently claimed invention also provides a method of forming a composite article as recited in claim <NUM> below.

The dependent claims define particular embodiments of each aspect.

Other aspects of the present disclosure will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. The accompanying figures are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labeled in every figure, nor is every component shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure.

The present disclosure generally relates to the synthesis and processing of nanostructures including nanotubes, composite materials comprising nanostructures, and related systems and methods. The claimed invention relates to methods of forming a composite article comprising substantially aligned nanostructures, as set forth in the appended claims. The following general disclosure is therefore set forth for illustration, information and context, and is intended neither to limit nor to extend the scope of protection beyond that claimed.

Generally, the present disclosure provides methods for uniform growth of nanostructures such as nanotubes (e.g., carbon nanotubes) on the surface of a substrate, wherein the long axes of the nanostructures may be substantially aligned. The nanostructures may be further processed for use in various applications, such as composite materials. For example, a set of aligned nanostructures may be formed and transferred, either in bulk or to another surface, to another material to enhance the properties of the material. In some cases, the nanostructures may enhance the mechanical properties of a material, for example, providing mechanical reinforcement at an interface between two materials or plies. In some cases, the nanostructures may enhance thermal and/or electronic properties of a material. In some cases, the aligned nanostructures may provide the ability to tailor one or more anisotropic properties of a material, including mechanical, thermal, electrical, and/or other properties. The present disclosure also provides systems and methods for growth of nanostructures, including batch processes and continuous processes.

The present disclosure provides systems and methods for producing substantially aligned nanostructures, having sufficient length and/or diameter to enhance the properties of a material when arranged on or within the material. Also, the nanostructures described herein may be uniformly dispersed within various matrix materials, which may facilitate formation of composite structures having improved mechanical, thermal, electrical, or other properties. The disclosed methods may also allow for continuous and scalable production of nanostructures, including nanotubes, nanowires, nanofibers, and the like, in some cases, on moving substrates. As used herein, the term "nanostructure" refers to elongated chemical structures having a diameter on the order of nanometers and a length on the order of microns to millimeters, resulting in an aspect ratio greater than <NUM>, <NUM>, <NUM>, <NUM>,<NUM>, or greater. In some cases, the nanostructure may have a diameter less than <NUM>, less than <NUM>, <NUM>, less than <NUM>, less than <NUM>, or, in some cases, less than <NUM>. Typically, the nanostructure may have a cylindrical or pseudo-cylindrical shape. In some cases, the nanostructure may be a nanotube, such as a carbon nanotube.

The disclosed methods may generally comprise growth of nanostructures on the surface of a growth substrate, wherein the growth substrate comprises a catalyst material positioned on or in the surface of the growth substrate. The growth substrate may have any shape, including substrates comprising a substantially flat surface or substrates comprising a non-planar surface. The growth substrate may be an elongated structure having a wide range of cross-sectional shapes, including square, rectangular, triangular, circular, oval, or the like. In some cases, the growth substrate may be a fiber, tow, strip, weave, or tape. In some cases, the growth substrate may be a cylindrical substrate, such as a fiber.

For example, <FIG> illustrates a fiber <NUM> having a diameter <NUM>. Catalyst material may be formed on the surface of the fiber, for example, as metal nanoparticles or precursors thereof, to form growth substrate <NUM>. Exposure of the growth substrate to a set of conditions selected to cause catalytic formation and/or growth of nanostructures on the surface of the growth substrate may produce a set of substantially aligned nanostructures <NUM> having a length <NUM> and positioned at a distance <NUM> from an adjacent nanostructure on the surface of the growth substrate.

<FIG> shows a schematic representation of a nanostructure growing from a catalyst material (e.g., nanoparticle) on a growth substrate. Catalyst material <NUM> is positioned on the surface of growth substrate <NUM>, and, when placed under a set of conditions selected to facilitate nanostructure growth, nanostructures <NUM> may grow from catalyst material <NUM>. Nanostructure precursor material <NUM> (e.g., a hydrocarbon gas, alcohol vapor molecule, or other carbon-containing species), may be delivered to growth substrate <NUM> and contact or permeate the growth substrate surface, the catalyst material surface, and/or the interface between the catalyst material and the growth substrate. In the growth of carbon nanotubes, for example, the nanostructure precursor material may comprise carbon, such that carbon dissociates from the precursor molecule and may be incorporated into the growing carbon nanotube, which is pushed upward from the growth substrate in general direction 108a with continued growth.

The set of substantially aligned nanostructures formed on the surface may be oriented such that the long axes of the nanostructures are substantially non-planar with respect to the surface of the growth substrate. In some cases, the long axes of the nanostructures are oriented in a substantially perpendicular direction with respect to the surface of the growth substrate, forming a nanostructure "forest. " As described more fully below, the alignment of nanostructures in the nanostructure "forest" may be substantially maintained, even upon subsequent processing (e.g., transfer to other surfaces and/or combining the forests with secondary materials such as polymers).

The present disclosure provides various composite articles comprising a first material layer, and a second material layer integrally connected to the first material layer, forming an interface of the material layers. The interface may comprise a set of nanostructures wherein the long axes of the nanostructures are substantially aligned and non-parallel to interface of the material layers. In some cases, the nanostructures may be dispersed uniformly throughout at least <NUM>% of the interface, or, at least <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the interface. As used herein, "dispersed uniformly throughout at least <NUM>% of the interface" refers to the substantially uniform arrangement of nanostructures over at least <NUM>% of the area of the interface. That is, the nanostructures are primarily arranged uniformly over the area of the interface, rather than in a heterogeneous arrangement of bundles or pellets.

In some cases, the nanostructures may be arranged such that nanostructures associated with the first material layer may penetrate into at least a portion of the second material layer. Similarly, nanostructures that may be associated with the second material layer may also penetrate into at least a portion of the first material layer. In this arrangement, the interface formed between the first material layer and the second material layer does not form a discrete and/or separate layer from the first and second material layers. Rather, the binding between the first material layer and the second material layer is strengthened by the interpenetration of nanostructures from both material layers. For example, <FIG> shows a composite article comprising a substrate <NUM> and a substrate <NUM>, wherein nanostructures <NUM> associated with a component (e.g., fiber) of substrate <NUM> penetrates the interface between substrate <NUM> and substrate <NUM> to contact at least a portion of substrate <NUM>. This entanglement between nanostructures of different substrates may reinforce the interface between the substrates. <FIG> shows a composite article <NUM> having a first material layer <NUM> and a second material layer <NUM>, joined to form an interface <NUM> wherein nanostructures of different material layers may entangle and reinforce the interface between the substrates.

The disclosure also provides composite articles comprising a substrate having a plurality of fibers associated with each other to form a cohesive structure, and a set of nanostructures arranged in association with the plurality of fibers. As shown in <FIG>, substrate <NUM> may comprise a plurality of fiber <NUM> having nanostructures <NUM> arranged substantially uniformly over the surface of the fiber. In some cases, the nanostructures may be arranged radially around and uniformly over a substantial majority of the surface of a fiber. Nanostructures of adjacent fibers may interact to reinforce the interactions between fibers, producing enhanced properties. In some cases, the nanostructures are dispersed essentially uniformly throughout the structure. For example, the structure may be a tow of fibers, a structure comprising interwoven or knit fibers, a weave, or other structure comprising a plurality of fibers in contact with one another to form a cohesive structure. The interaction of nanostructures from adjacent fibers may enhance the properties of the composite article, reinforcing the interaction between individual fibers. In some cases, the structure comprises a set of fibers exposed at the surface of the substrate and a set of fibers not exposed at the surface of the substrate, i.e., the fibers are positioned in an interior location within the substrate. In other cases, the substrate might comprise an arrangement of fibers such that an individual fiber may comprise one or more portions exposed at the surface of the substrate and one or more portions not exposed at the surface of the substrate. For example, as shown in <FIG>, article <NUM> comprises a plurality of fibers arranged in a woven pattern, when an individual fiber may comprise a portion that is exposed at the surface of article <NUM> and another portion which is in contact with or covered by another fiber such that the portion is not exposed at the surface. As shown in <FIG>, fiber <NUM> may comprise nanostructures dispersed essentially uniformly over the surface area of the fibers such that nanostructures of fiber <NUM> may interact with nanostructures of adjacent fiber <NUM>.

The ability to arrange nanostructures essentially uniformly throughout structures comprising plurality of fibers allows for the enhanced mechanical strength of the overall structure. For example, in other known systems comprising a plurality of fibers forming a cohesive structure, nanostructures or other reinforcing materials may only be arranged on the surface of the structure, and not within interior portions of the structure. Where one or more fibers are associated with each other to form a cohesive structure as the substrate, the "surface" of the substrate refers to an outermost continuous boundary defined at the outer extremities of the substrate. For example, the substrate may comprise an upper continuous boundary and a lower continuous boundary, such that a mesh of fibers, or portions of fibers, are disposed between the upper and lower continuous boundaries and do not extend beyond the upper and lower continuous boundaries. That is, the surface of the substrate may not, in some cases, refer to the topological surface of the substrate, i.e., does not refer to the portion of the substrate that may be first contacted by a species introduced to the substrate from a direction perpendicular to the surface of the substrate. Rather the "surface" may refer to a plane defined at the outermost extremities of the substrate. As shown in <FIG>, for example, the "surface" of article <NUM> is shown by plane 950A. Similarly, as shown in <FIG>, the "surface" of article <NUM> is shown by plane 960A.

The present disclosure also provides methods for forming composite articles, wherein the composite articles comprise nanotubes, or other nanostructures, positioned within the composite article for the enhancement of one or more properties of the composite article. Such methods may be embodiments of the invention. For example, in embodiments of the invention, the nanostructures are positioned to contact at least two substrates of an article. In some cases, an article may comprise a first component and a second component, each component comprising nanostructures, such that the interaction of nanostructures of different components may enhance properties of the article. In some cases, the nanostructures may be arranged to enhance the intralaminar interactions of components within a material or substrate. In some cases, the nanostructures may be arranged to enhance the interlaminar interactions of two substrates or plies within a composite structure. In embodiments of the invention, the nanostructures are positioned at an interface between the two substrates, and accordingly the nanostructures may mechanically strengthen or otherwise enhance the binding between the two substrates.

In some embodiments of the invention, the method comprises providing a first and a second substrate, each having a joining surface, and arranging a set of substantially aligned nanostructures on or in the joining surface of at least one of the first and second substrates. The first and second substrates may then be bound to each other via their respective joining surfaces to form an interface of the substrates, wherein the interface comprises the set of substantially aligned nanostructures. In some cases, the nanostructures are dispersed uniformly on or in at least <NUM>% of the joining surface, or, in some cases, at least <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% of the joining surface. As used herein, "dispersed uniformly on or in at least <NUM>% of the joining surface" refers to the substantially uniform arrangement of nanostructures over at least <NUM>% of the area of the joining surface.

In some cases, the arranging comprises catalytically forming nanostructures on the surface of at least one of the first and second substrates. The nanostructures may be arranged on the surface of a substrate either alone or in combination with one or more support materials. For example, a set of nanostructures may be provided on a growth substrate and may be contacted with at least one of the first and second substrates such that the set of substantially aligned nanostructures may be arranged on or in the joining surface of the substrates. The growth substrate may comprise the nanostructures as freestanding nanostructures or in combination with a support material such as a polymer material, carbon fibers, or the like. The growth substrate may optionally be separated from the set of substantially aligned nanostructures on or in the joining surface, prior to binding of the first and second substrates to each other. In some cases, the substrate may be a fiber, prepreg, resin film, dry weave, or tow. At least one of the first and second substrate may be a prepreg comprising fibers and a polymer material (e.g., epoxy). The substrate may further comprise various materials, such as conducting materials, fibers, weaves, or nanostructures (e.g., nanotubes) dispersed throughout the substrate.

In some cases, composite material may exhibit a higher mechanical strength and/or toughness when compared to an essentially identical material lacking the set of substantially aligned nanostructures, under essentially identical conditions. In some cases, composite material may exhibit a higher thermal and/or electrical conductivity when compared to an essentially identical composite material lacking the set of substantially aligned nanostructures, under essentially identical conditions. In some cases, the thermal, electrical conductivity, and/or other properties (e.g., electromagnetic properties, specific heat, etc.) may be anisotropic.

Upon arranging the nanostructures on one or more joining surfaces, the method may further comprise adding one or more support materials to the nanostructures on the joining surface. The support materials may provide mechanical, chemical, or otherwise stabilizing support for the set of nanostructures. In some cases, the support material may be a monomer, a polymer, a fiber, or a metal, and may be further processed to support the nanostructures. For example, a mixture of monomeric species may be added to the nanostructures, and subsequent polymerization of the monomeric species may produce a polymer matrix comprising the nanostructures disposed therein. As shown in <FIG>, growth substrate <NUM> may comprise nanostructures <NUM>. One or more support materials may be added to the nanostructures to form a support material (e.g., matrix) such that the nanostructures are dispersed within the support material <NUM>. Growth substrate <NUM> may then be removed to produce a self-supporting structure with the nanostructures dispersed throughout the structure, with retention of the original alignment of nanostructures. As used herein, a "self-supporting structure" refers to a structure (e.g., solid, non-solid) having sufficient stability or rigidity to maintain its structural integrity (e.g., shape) without external support along surfaces of the structure. Of course, it should be understood that a support material may not be required to form a self-supporting structure. In some cases, a set of nanostructures, such as a carbon nanotube forest, may form a self-supporting structure without need of a support material, and may be manipulated as a film.

<FIG> shows a method for forming various composite materials. Growth substrate <NUM> may comprise a set of nanostructures <NUM> and substrate <NUM> may comprise a joining surface <NUM> A, wherein the joining surface comprises a polymer material such as epoxy. Growth substrate <NUM> may be contacted with substrate <NUM> such that nanostructures <NUM> penetrate the polymer material of joining surface 18A. In some cases, the epoxy material may interact with nanostructures via capillary action, such that at least a portion or, in some cases, substantially all, of the length of nanostructures <NUM> penetrate into joining surface 18A to form interface 18B comprising both the polymer material and the nanostructures. This may form one type of composite structure. Alternatively, upon formation of interface layer 18B, growth substrate <NUM> may be detached from the nanostructures and a new substrate <NUM> may be bound to layer 18B to form a hybrid composite structure <NUM>, wherein the nanostructures may contact both substrates. In some cases, as shown in <FIG>, a first substrate <NUM> and a second substrate <NUM> may each comprise nanostructures and a polymer material positioned at joining surfaces <NUM> and <NUM>, respectively, such that binding of the first and second substrates via their respective joining surfaces may produce a composite material <NUM> comprising an interface <NUM>, wherein the interface comprises a set of substantially aligned nanostructures and a polymer material.

In embodiments of the invention, the nanostructures are arranged on a joining surface of at least one of the first and second substrates. This may be followed by addition of a binding material, such as epoxy. The binding material may be introduced at the interface between the first and second substrates, or may be diffused through the bulk of the first and/or second substrates to the interface.

In embodiments of the invention, the first and second substrates are a prepreg materials comprising, for example, fibers such as carbon fibers. In some cases, the length of the nanostructures may be approximately equal to or greater than the diameter of the fibers within the prepreg, or may be greater than half the distance between neighboring fibers or plies in the composite material, so as to give sufficient reinforcement between the neighboring plies.

The disclosed methods may also comprise providing a substrate (e.g., growth substrate) comprising a plurality of fibers associated with each other to form a cohesive structure. The substrate may comprise a catalytic material as described herein, such that a set of nanostructures may be arranged in association with the plurality of fibers such that the nanostructures are dispersed essentially uniformly throughout the structure. As used herein, "dispersed essentially uniformly throughout the structure" refers to the substantially uniform arrangement of nanostructures through the bulk of the structure, including both the topological surface of the substrate and interior portions of the substrate. For example, the structure may be a tow of fibers or a weave. In some cases, at least <NUM>% of the fibers have nanostructures attached essentially uniformly across their surfaces. In some cases, at least <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or a substantially majority (e.g., substantially all) of the fibers have nanostructures attached essentially uniformly across their surfaces. This advantageously produces a substrate comprising nanostructures arranged within interior locations of the substrate, rather than only at the surface or topological surface. In some cases, carbon nanotubes may be grown on fiber tows or mats before the tows or mats are used in various composite processing routes (e.g., filament winding or resin-transfer molding, RTM). Alternatively, the substrate may be a single fiber wherein portions of the fiber or other fibers may be arranged to form the cohesive structure (e.g., a knot, twisted fiber, etc.).

<FIG> shows a sample of alumina cloth in different stages of carbon nanotube growth, including (a) an un-coated alumina cloth, (b) the alumina cloth after application of the catalyst material, (c) the alumina cloth with a conditioned catalyst, and (d) carbon nanotubes grown on the surface of the fibers in the cloth.

The disclosed methods may be useful producing composite materials, such as those produced according to embodiments of the invention, having enhanced properties, such as mechanical strength. The integrity of the reinforcement may depend on the diameter and/or length of the nanostructures (e.g., nanotubes), as shown by the graph of the resistance ratio as a function of nanostructure radius in <FIG>. The disclosed nanostructures may have the appropriate dimensions to enhance the properties of such materials. In some cases, the nanostructures may have a diameter of <NUM> or less, or, in some cases, <NUM> or less, producing significant toughening of the material, for example, by <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>,<NUM>%, or greater. For example, a <NUM>% increase in shear strength was observed for materials having intralaminar carbon nanotube interactions, and a <NUM>% increase in the fracture toughness for materials having interlaminar carbon nanotube interactions, have been observed, as described more fully below. The length of the nanostructures can be also controlled through the growth kinetics to create nanostructures capable of interacting (e.g., entangling) with one another upon incorporation of a support material. In this way, the interface layer between components of a composite structure may be reinforced and the mechanical properties (e.g., elastic and strength/toughness) of the composite structure may be significantly increased. In some cases, the electrical conductivity, thermal conductivity, and other properties of a composite structure may also be enhanced or made anisotropic by the disclosed structures and methods. This may be useful in, for example, the manufacture of aircrafts, including applications for lightning protection of non-conductive advanced composites.

Advantageously, the nanostructures may be uniformly wetted by various materials, including polymeric materials such as epoxy. For example, when a set of aligned nanostructures is contacted with a cured or uncured epoxy layer, strong capillary interactions may cause the epoxy to rapidly and uniformly "wick" into the spaces between the nanostructures, while maintaining alignment among the nanostructures. In some cases, adhesion strength of <NUM> MPa or more have been measured by pulling nanostructures from a matrix using a scanning probe tip, which exceeds the interfacial strength in known systems. For example, a composite microstructure of SU-<NUM> comprising <NUM> weight % of aligned carbon nanostructures fabricated by the methods described herein, may have a stiffness of <NUM> GPa compared to <NUM> GPa for pure SU-<NUM>, indicating a significant reinforcement with carbon nanostructure stiffness exceeding <NUM> GPa.

Alternatively, the set of aligned nanostructures may also be used to reinforce an interface or joint connecting two materials. <FIG> shows a configuration wherein the placement of a nanostructure "pillar" at an interface between two materials reinforces the two materials. For example, a pattern of nanostructure "pillars" <NUM>, may be grown on a substrate to a height h, which may be the sum of the thickness of the two materials used to join substrates <NUM> and <NUM>. Substrates <NUM> and <NUM> may be joined together using a joint <NUM>. Both materials may have holes (or other features) <NUM> aligned and spaced in a manner that may allow the nanostructure pillars to fit in the holes. The holes may then be filled with a matrix (e.g., a polymer resin) <NUM> which may adhere the nanostructure pillar to both materials <NUM> and <NUM>.

As described herein, the present disclosure provides methods for the growth and fabrication of nanostructures, including nanotubes. <FIG> shows a schematic representation of stages in the process of manufacturing a film of nanostructures, such as a "forest" of carbon nanotubes, on a growth substrate. In the first stage <NUM>, the catalyst material (e.g., metal catalyst material) may be deposited onto growth substrate <NUM> as film <NUM>. Film <NUM> may be formed directly on growth substrate <NUM>, or may be formed on an intermediate layer <NUM> formed on growth substrate <NUM>, and film <NUM> may be treated to form catalyst material nanoparticles <NUM>. Alternatively, the nanoparticles may be deposited directly on the substrate <NUM>, with or without intermediate layer <NUM>. In second stage <NUM>, the nanoparticles <NUM> may be thermally and chemically treated in preparation for the growth of nanostructures. The treatment may include sequential exposure to oxidizing (e.g., inert or O<NUM>-containing) and reducing (H<NUM>-contatining) atmospheres at elevated temperature. If a film of metal catalyst is deposited in stage <NUM>, the film may coarsen into nanoparticles during stage <NUM>. In stage <NUM>, the growth substrate may be exposed to a nanostructure precursor material under a set of conditions such that nanostructures <NUM> (e.g., carbon nanotubes) begin forming or "nucleate" from the catalyst material. In stage <NUM>, the set of conditions may be maintained as the nanostructures <NUM> grow into a film or "forest" <NUM> to a desired height h <NUM>.

As used herein, exposure to a "set of conditions" may comprise, for example, exposure to a particular temperature, pH, solvent, chemical reagent, type of atmosphere (e.g., nitrogen, argon, oxygen, etc.), electromagnetic radiation, or the like. In some cases, the set of conditions may be selected to facilitate nucleation, growth, stabilization, removal, and/or other processing of nanostructures. In some cases, the set of conditions may be selected to facilitate reactivation, removal, and/or replacement of the catalyst material. In some cases, the set of conditions may be selected to maintain the catalytic activity of the catalyst material. The set of conditions may comprise exposure to a source of external energy. The source of energy may comprise electromagnetic radiation, electrical energy, sound energy, thermal energy, or chemical energy. For example, the set of conditions comprises exposure to heat or electromagnetic radiation, resistive heating, exposure to a laser, or exposure to infrared light. The set of conditions may comprise exposure to a particular temperature, chemical species, and/or nanostructure precursor material. In some cases, the set of conditions comprises exposure to a temperature between <NUM>-<NUM>.

In some cases, a source of external energy may be coupled with the growth apparatus to provide energy to cause the growth sites to reach the necessary temperature for growth. The source of external energy may provide thermal energy, for example, by resistively heating a wire coil in proximity to the growth sites (e.g., catalyst material) or by passing a current through a conductive growth substrate. In some case, the source of external energy may provide an electric and/or magnetic field to the growth substrate. In some cases, the source of external energy may provided via laser, or via direct, resistive heating the growth substrate, or a combination of one or more of these. The set of conditions may comprise the temperature of the growth substrate surface, the chemical composition of the atmosphere surrounding the growth substrate, the flow and pressure of reactant gas(es) (e.g., nanostructure precursors) surrounding the substrate surface and within the surrounding atmosphere, the deposition or removal of catalyst material, or other materials, on the surface of the growth surface, and/or optionally the rate of motion of the substrate.

In some cases, the nanostructures may be grown on the growth substrate during formation of growth substrate itself. For example, fibers such as Kevlar and graphite may be formed in a continuous process, in combination with nanostructure fabrication as described herein. ICarbon fibers comprising nanostructures on the surface of the fibers may be formed at elevated temperature by first stabilizing the carbon fiber precursor material (pitch or PAN), typically under stress at elevated temperature, followed by carbonization and or graphitization pyrolysis steps at very elevated temperatures (e.g., greater than <NUM>) to form the fiber. The nanostructures may be grown on the surface of the fibers, followed by surface treatments, sizing, spooling, or other processing techniques. In some cases, the method may comprise the act of removing the nanostructures from the growth substrate. For example, the act of removing may comprise transferring the nanostructures directly from the surface of the growth substrate to a surface of a receiving substrate. The receiving substrate may be, for example, a polymer material or a carbon fiber material. In some cases, the receiving substrate comprises a polymer material, metal, or a fiber comprising Al<NUM>O<NUM>, SiO<NUM>, carbon, or a polymer material.

In some cases, the receiving substrate comprises a fiber comprising Al<NUM>O<NUM>, SiO<NUM>, carbon, or a polymer material. In some cases, the receiving substrate is a fiber weave. Removal of the nanostructures may comprise application of a mechanical tool, mechanical or ultrasonic vibration, a chemical reagent, heat, or other sources of external energy, to the nanostructures and/or the surface of the growth substrate. In some cases, the nanostructures may be removed by application of compressed gas, for example. In some cases, the nanostructures may be removed (e. detached) and collected in bulk, without attaching the nanostructures to a receiving substrate, and the nanostructures may remain in their original or "as-grown" orientation and conformation (e.g., in an aligned "forest") following removal from the growth substrate.

<FIG> shows the continuous transfer of nanostructures from a growth substrate to a receiving substrate. The layer of nanostructures <NUM> may be detached from growth substrate <NUM> and placed on receiving substrate <NUM>, wherein motion of one or both of the substrates, and/or action from a mechanical, chemical, or thermal process, may facilitate the transfer. For example, growth substrate <NUM> may be rotated in a direction <NUM>. Prior to or simultaneous to the transferring act, a layer of nanostructures may also be grown on a portion <NUM> of growth substrate. The growth substrate may be a roller or cylindrical drum, where portions of the growth substrate may be processed in distinct thermal and atmospheric "zones" to facilitate arrangement of growth sites, treatment of the growth sites, and growth of nanostructures on the roller surface, while transfer may occurs in a different region of the growth substrate. The growth substrate may be continuously rotated to enable growth of a new layer of nanostructures on the surface of the growth substrate where the nanostructures have been removed by the transfer process. As shown in <FIG>, rotary motion in a direction <NUM> of the growth substrate may be matched to translation of the second substrate, which in this case is flat.

An external force, may be used to initiate and continue delamination of the layer from the first substrate, and to direct the layer toward the second substrate. For example a scraping ("doctor") or peeling blade, and/or other means such as an electric field may be used to initiate and continue delamination. In some cases, the layer may be delaminated and/or handled as a film, tape, or web. The layer may contact the second substrate before or instantly when it is detached from the first substrate, so there is no suspended section and therefore the first substrate is "rolling" layer film onto the second substrate. Attractive forces between the layer and the second substrate, such as an adhesive or a resin which wets the layer upon contact, or an electric field applied between the layer and the second substrate, may assist transfer. Alternatively, the film may be suspended, handled, and optionally mechanically (e.g., rolled, compacted, densified), thermally or chemically (e.g., purified, annealed) treated in a continuous fashion prior to being transferred to the second substrate. In some cases, the second substrate is a composite ply, such as a weave of carbon or polymer fibers. An interface <NUM> between the layer of nanostructures and the second substrate, may for example be strengthened by simultaneous or subsequent application of a binder or adhesive material which establishes uniform and strong attachment between the nanostructures and the second substrate. Alternatively, the interface may be strengthened by application of energy, such as by thermal annealing, induction heating, by irradiation using microwave or treatment in an electric or magnetic field, or by application of fluid and/or mechanical pressure, and by combination of one or more of these or other related methods. The second substrate can be made of any suitable material, such as a polymer film (e.g., to give a flexible support), metal foil (e.g., to achieve electrical contact to the layer of nanostructures), and/or the second substrate can previously be coated with another layer of nanostructures, and/or this process may be repeated many times with layers of the same or different properties to give multilayered architectures.

In some cases, the nanostructures may be grown or fabricated in batch processes. That is, a set of nanostructures may be grown on a majority of the surface of the growth substrate and may be further processed in one or more steps as described herein to produce a set of nanostructures arranged on the surface of a substrate. In batch processes, one set of nanostructures may be produced per growth substrate in series of fabrication steps, as described herein, wherein the growth substrate may subsequently, be reused, or the catalyst material may be regenerated or replaced, to form another set of nanostructures.

The present disclosure also provides methods for the continuous formation of nanostructures, such as carbon nanotubes. As used herein, the term "continuous" refers to the ability to perform one or more different processes on different portions of a single growth substrate simultaneously, such as growth and removal of nanostructures, or growth of nanostructures and reactivation of the catalyst material. The term "continuous" may also refer to the recirculation of a single growth substrate through more than one iteration of a series of steps to grow, process, and detach or transfer nanostructures. In some cases, a growth substrate may be described as having a "topologically continuous" surface, such that each region in the system may interact with at least a portion of the growth substrate at all times during operation, i.e., as the growth substrate is recirculated (e.g., rotated) within the system. As used herein, "topologically continuous" means continuous in the sense that a particular surface on a growth substrate forms a continuous pathway around or through the structure. Examples of growth substrates having a topologically continuous surface include, but are not limited to, cylinders, flexible belts or bands, or structures having a surface that forms a closed curve or loop structure.

The method may involve providing a growth substrate with a surface comprising a catalytic material, as described herein. The growth substrate may be continuously moved through an apparatus constructed and arranged to facilitate continuous growth of nanostructures on the growth substrate and removal of nanostructures from the growth substrate. In some cases, a first portion of the growth substrate may be exposed to a set of conditions selected to cause catalytic formation of nanostructures on the surface. For example, the set of conditions may comprise exposure to a nanostructure precursor and/or a source of external energy. While exposing the first portion of the growth substrate to the set of conditions, a second portion of the growth substrate may be treated to remove the nanostructures from the surface of the growth substrate. The exposing and removing acts with said growth substrate may be repeated, in some cases, at least one time, at least two times, at least <NUM> times, at least <NUM> times, at least <NUM> times, or more.

In some cases, while exposing the first portion of the growth substrate to the first set of conditions, the method may comprise treating a second portion of the growth substrate to a second set of conditions selected to reactivate the first catalyst material. For example, the method may comprise contacting one or more chemical species with the first catalyst material to reactivate (e.g., oxidize, reduce, etc.) the first catalyst material. In some cases, while exposing the first portion of the growth substrate to the first set of conditions, the method may comprise treating a second portion of the growth substrate to a second set of conditions selected to replace the first catalyst material with a second catalyst material. The first catalyst material may be used multiple times (e.g., at least twice, at least <NUM> times, at least <NUM> times, or more) before being replaced with a second catalyst material. In some cases, the act of exposing comprises continuous rotation of a cylindrical growth substrate, flowing a nanostructure precursor material through the porous growth substrate, or flowing a chemical species through the porous growth substrate to treat the catalyst material. The chemical species may activate the catalyst material prior to growth of the nanostructures, or may reactivate the catalyst material after growth of the nanostructures. In some cases, the chemical species reduces or oxidizes the catalyst material after growth of the nanostructures.

Removal of the catalyst material may be performed mechanically, including treatment with a mechanical tool to scrape or grind the first catalyst material from the surface of the growth substrate. In some cases, the first catalyst material may be removed by treatment with a chemical species (e.g., chemical etching) or thermally (e.g., heating to a temperature which evaporates the catalyst). A second catalyst material may be deposited by printing/spraying of a catalyst precursor solution on the growth substrate. For example, a metal salt solution may be sprayed or printed on the growth catalyst. In other cases, the growth substrate may be treated with a solution containing preformed metal nanoparticles. For example, the growth substrate may be treated with metal nanoparticles as described in <NPL>.

A composite Fe/Al<NUM>O<NUM> substrate, which may be made by sintering nanoscale Fe and Al<NUM>O<NUM> powders, can be mechanically polished to expose a new layer of catalyst. Alternatively, the growth substrate may be heated beyond a temperature at which Fe evaporates, and the growth substrate may be subsequently coated with a new layer of catalyst material, for example, by contact printing. It should be understood that, in some cases, it may not be necessary to replace the catalyst material. That is, the activity of the catalyst material may be placed under a set of conditions selected to maintain continuous catalyst activity through multiple iterations of nanostructure growth and removal.

<FIG> shows a schematic representation of recirculation of a growth substrate for continuous growth of nanostructures from catalyst particles ("growth sites") on the growth substrate. Growth substrate <NUM> is optionally coated with an intermediate layer <NUM> and catalyst material <NUM> to form growth substrate <NUM> A, or, with catalyst nanoparticles <NUM> to form growth substrate 205B. Next, the substrate may be thermally and/or chemically treated to prepare the growth sites for growth of nanostructures, on growth substrate <NUM>. Next, nanostructures <NUM> may be grown from the growth sites of growth substrate <NUM>. The nanostructures <NUM> may then be removed from growth substrate <NUM>, for example, using mechanical tool <NUM>, while leaving a sufficient amount of the catalyst on the substrate. It should be understood that, while individual nanostructures are shown, the removal process may involve removal of a film of nanostructures (e.g., a "forest") held together by physical entanglement and surface interactions. Next, the substrate may be thermally and/or chemically treated to return the growth substrate to the same state as in growth substrate <NUM>, or the growth sites and/or intermediate layer may be removed return the growth substrate to the same state as in growth substrate <NUM>, and the cycle may be repeated. Examples of intermediate layers are described in, for example, <NPL>, incorporated herein by reference.

The present disclosure also provides systems for growing nanostructures. The system may comprising a growth substrate with a surface suitable for growing nanostructures thereon, a region able to expose the surface of the growth substrate, or portion thereof, to a set of conditions selected to cause catalytic formation of nanostructures on the surface of the growth substrate, and a region able to expose the surface of the growth substrate, or portion thereof, to a set of conditions selected to remove nanostructures from the surface of the growth substrate, in some cases, without substantial removal of the catalyst material from the growth substrate. That is, a sufficient amount of catalyst material may remain on the surface of the growth substrate after removal of the nanostructures such that nanostructures may be grown on the same growth substrate in subsequent processes. In some cases, the system optionally comprises a region able to expose the surface of the growth substrate, or portion thereof, to a set of conditions selected to reactivate the first catalyst material or replace the first catalyst material with a second catalyst material. The system may also comprise a region able to expose the surface of the growth substrate, or portion thereof, to a set of conditions selected to chemically treat catalyst material on the surface of the growth substrate.

The nanostructures may be grown on at least a portion of the surface of the growth substrate (e.g., the outer surface of the a rigid ring) to produce a seamless film of nanostructures, which may be removed as the growth substrate is continuously recirculated.

The system may comprise a growth substrate constructed and arranged to for use as a recirculating substrate. In some cases, the growth substrate may be shaped to form a rigid ring, such that the method is performed by continuous rotation of the rigid ring. In some cases, the growth substrate may be a flexible belt (e.g., metal foil, thin ceramic), such that rotation of the flexible belt around a set of rollers may allow for continuous formation and/or transfer of nanostructures on one or more portions of the growth substrate. The system may comprise additional components to facilitate the continuous production of nanostructures. In some cases, the system comprises at least one or more support rollers and/or drive rollers, at least one set of electrical contacts associated with the growth substrate,.

An advantageous feature of systems and methods for continuous growth of nanostructure may be that the growth substrate is continuously recirculated. That is, the growth substrate may be a single, movable component, rather than a number of individual growth substrates placed on a moving components. That is, the nanostructures may be grown directly on the moving growth substrate, and conditions at various portions of the moving growth substrate may be individually monitored and controlled.

Accordingly, in some cases, methods for continuous growth of nanostructures may involve exposing a growth substrate, or portion thereof, to a series of regions, wherein each region comprises a set of conditions to perform a particular step in the process, to achieve the continuous growth and removal of nanostructures using the same growth substrate, along with necessary thermal, mechanical, and chemical treatment of the substrate to enable recirculation of the substrate and continued growth of nanostructures. The growth substrate may be moved through various regions of the system. For example, in a first region, the growth substrate may be initially heated and/or the catalyst material may be processed (e.g., to form nanoparticles from a catalyst film and/or to chemically reduce the catalyst material). In a second region, the nanostructures may be nucleated by exposure of the growth substrate to a nanostructure precursor material, wherein the growth of the nanostructures may be monitored optically. In a third region, the formed nanostructures may be removed by any method suitable for a particular application. Upon removal of the nanostructures from the growth substrate, the growth substrate may be recirculated (e.g., by rotation of the growth substrate, by backward translation of the growth substrate, etc.) and repeated growth of nanostructures may be conducted. In some cases, the continuous growth scheme may involve linear translation of the growth substrate. In some cases, the continuous growth scheme may involve rotational translation of the growth substrate, wherein the nanostructures may be continuously delaminated as the growth substrate rotates. In some cases, the growth substrate, or portions thereof, may be locally heated by resistive heating, laser heating, or exposure to electromagnetic radiation (e.g., infrared light). In other cases, the substrate may be placed in a furnace or other enclosure for thermal and/or atmospheric control.

One advantage of a continuous method may be the ability to uniformly grow nanostructures over a relatively large surface area and to collect the nanostructures in bulk and/or to transfer these nanostructures to other substrates (e. g, tows and weaves of advanced fibers). This may allow for industrial production of nanostructure materials, and other nanostructures. This may also be advantageous for industrial production of nanostructure-reinforced hybrid materials which exhibit significant increases in bulk properties such as interlaminar toughness, shear strength, and thermal conductivity.

<FIG> shows a schematic representation of a system for growth of nanostructures. Growth substrate <NUM>, shown here as a hollow cylinder in cross-section, may be optionally coated with an intermediate layer <NUM> (e.g., a ceramic such as Al<NUM>O<NUM>), along with catalyst nanoparticles <NUM>. A layer of nanostructures <NUM> may be grown on the surface of the growth substrate, which may be continuously rotated in a direction <NUM>. As the growth substrate is moved the catalyst particles may pass through two or more regions of the system which may be maintained with selected thermal and atmospheric conditions. The catalyst may be chemically and thermally pretreated in one or more regions, such as regions <NUM>, <NUM>, and <NUM>, for example. In some cases, the growth substrate may be heated to up to <NUM> in an atmosphere comprising H<NUM> or another inert carrier gas such as Ar or He. In region <NUM>, the nanostructures may be grown as described herein at a temperature of up to <NUM>, and in some cases, between <NUM>-<NUM>. The growth substrate may be electrically conductive and may be heated resistively to a desired temperature in the presence of, for example, a mixture Of C<NUM>H<NUM> and H<NUM>, for the growth of carbon nanotubes.

In region <NUM>, the nanostructures may be post-treated by, for example, a mechanical tool used to compact or densify the nanostructures. Alternatively, the nanostructures may be heated to anneal the nanostructures by application of radiant heat. In region <NUM>, the nanostructures may be removed from the growth substrate by mechanical means, such as a razor blade or vibration, including surface, acoustic, or ultrasonic waves. The nanostructures may be removed by chemical processes, i.e., by etching the interface between the nanostructures and the growth substrate using an oxygen-containing atmosphere, where the growth substrate is maintained at a temperature sufficient to cause this etching.

In some cases, a combination of one or more of these processes may be used.

In region <NUM>, the catalyst material may be removed from the growth substrate, by exposing the growth substrate to a chemical atmosphere (e.g., a gas or liquid) to dissolve or detach the catalyst and/or supporting layer from the growth substrate. Alternatively, the growth substrate is heated to a sufficient temperature (e.g., by infrared means or by resistive heating) to cause evaporation of the catalyst and/or supporting layer. The catalyst and/or supporting layer may also be removed by mechanical means, such as contact with an abrasive wheel as shown <NUM>, where the wheel may move in and out of contact with the growth substrate. In region <NUM>, the catalyst may optionally be reactivated as described herein. In region <NUM>, the catalyst material and/or supporting material may be applied to the growth substrate. For example, the catalyst material may be applied onto the growth substrate by electron beam evaporation or sputtering under vacuum atmosphere. Alternatively, the materials may be applied via roller <NUM>, which may be coated with catalyst nanoparticles, by methods described herein.

<FIG> shows a schematic representation of a growth substrate which may be heated resistively using rolling electrical contacts, and where adjacent zones may have independent thermal control by passing independently controlled electrical currents through the respective electrical contacts between neighboring zones. A section of the continuous growth substrate, <NUM>, is shown, along with a series of rotating contact elements, such as <NUM> and <NUM>. The substrate may move from left to right, and the contact elements may rotate to drive and/or permit this motion. The contacts on the bottom surface of the substrate may be electrically conductive, and may be held at suitable voltage to drive suitable current through the substrate, which can cause resistive heating of the substrate. For example, contact <NUM> may be held at voltage V<NUM>, contact <NUM> may be held at voltage V<NUM>, and contact <NUM> may be held at voltage V<NUM>. Thermal zones, <NUM> and <NUM> are also shown, where passage of independently controlled currents through respective sections of the substrate may enable maintenance of the substrate surface in each zone at independently controlled temperatures. For example, a non-contact temperature sensors such as an infrared sensor shown as <NUM> may be used to measure the temperature at a particular location of the substrate (many sensors may be used and/or scanned to measure temperature at multiple locations), and the output of this sensor may be used to control the temperature by controlling the current applied to heat the substrate in the respective zone. <FIG> shows that the top contacts may touch only the edges of the substrate, so the top surface <NUM> may remain uncovered for growth of nanostructures on this surface.

<FIG> shows a schematic representation of a growth substrate where neighboring atmospheric zones may be isolated using differential pressure and flow seals, where the gas may be supplied from the surface of the substrate on which nanostructures are grown. Above substrate <NUM>, three chambers may be maintained; chamber <NUM> may provide a first pressure-driven flow through a uniform arrangement of orifices and the flow may reach the substrate surface primarily in the first region <NUM>. Flow from chamber <NUM> may reach the substrate surface primarily in the second region <NUM>. In between the chambers, flow may be drawn from near the substrate surface, into chamber <NUM>, where chamber <NUM> may be obtained at a reduced pressure to as to draw flow from both regions near the substrate surface. At the entry to <NUM>, the flows from both regions mix in the small substrate area <NUM>; however, flow which has interacted with the substrate in region <NUM> may not interact with region <NUM>, therefore isolating the processing atmospheres between these neighboring regions. For example, chamber <NUM> may have an atmosphere <NUM> of H<NUM>/He, for pre-treating a supported catalyst Of Fe/Al<NUM>O<NUM> for carbon nanotube growth, and chamber <NUM> may have an atmosphere of C<NUM>H<NUM>/H<NUM>, for growing carbon nanotubes as shown <NUM> on the substrate surface. The carbon nanotubes may begin growing when the substrate surface passes under the outlet orifices of chamber <NUM> and may be thereby exposed to the carbon-containing reactant atmosphere. The substrate may be heated resistively as shown in <FIG>.

<FIG> shows a schematic representation of a growth substrate where neighboring atmospheric zones may be isolated using differential pressure and flow seals, where the gas may be supplied through pores or holes in the substrate. Substrate <NUM> can have pores or holes <NUM> and flow may be directed through these cavities from the opposite side of the substrate, and where the top surface <NUM> of the substrate may be treated for growth of nanostructures and other steps herein disclosed. Independent atmospheres <NUM> and <NUM> may be isolated on the back side of the substrate, and the atmospheres may be isolated by rolling contact <NUM> in contact with divider <NUM> along with seal <NUM> which permits motion between the contact and the divider. Above the top surface of the substrate, the flows may be drawn into chamber <NUM> as flow <NUM>.

Those of ordinary skill in the art would appreciate that systems for continuous growth of nanostructures may contain any number of processing zones as described herein. In some cases, two or more zones may be operated simultaneously and/or under different conditions, depending on a particular application. For example, the conditions of the catalyst and substrate, as determined by in situ monitoring of the catalyst, substrate, and/or nanostructures before or after removal from the substrate, may be varied at different portions of the growth substrate. Systems and methods for continuous growth of nanostructures may also be used in combination with other methods, including those described in <NPL>; <NPL>; and <NPL>, which are incorporated herein by reference.

In some cases, the characteristics of the nanostructures, catalyst material, and/or growth substrate surface may be monitored during operation of the system, which may facilitate in selecting and/or controlling conditions for production of nanostructures. The system may be monitored by measuring the electrical conductivity or impedance of the growth substrate or catalyst material by Raman or infrared spectroscopy of the nanostructures, by X-ray scattering from the nanostructures, catalyst, or substrate, and/or by measurement of the thickness of the nanostructure layer and/or the length or diameter of nanostructures on the substrate surface.

In some cases, the method comprises providing a first and a second prepreg composite ply, each having a joining surface, and arranging a set of substantially aligned nanotubes on or in the joining surface of at least one of the first and second composite plies as described herein. For example, the nanotubes may be dispersed uniformly on or in at least <NUM>% of the joining surface. The method may further comprise binding the first and second composite plies to each other via their respective joining surfaces to form an interface of the plies, wherein the interface comprises the set of substantially aligned nanotubes. The prepreg(s) may then be cured to bind the nanotubes and prepreg composite plies.

The disclosed methods may comprise additional processing steps to suit a particular application. For example, nanostructures may be formed on a substrate as described herein, such that the long axes of the nanostructures are substantially aligned in an orientation that is non-parallel to the surface of the substrate. The nanostructures and/or substrate may be further treated with a mechanical tool to change the orientation of the nanostructures such that the long axes of the nanostructures are substantially aligned in an orientation that is parallel to the surface. Such substantially aligned nanostructured may be applied in embodiments of the invention, which provide an interface between first and second substrates comprising a set of substantially aligned nanostructures. <FIG> show processes for creating a composite ply comprising fibers and aligned and evenly distributed nanostructures. In <FIG>, a set of aligned nanostructures <NUM> of height h may be grown on growth substrate <NUM>, wherein the long axes of the nanostructures are oriented substantially perpendicular to the surface of growth substrate <NUM>. A roller <NUM>, or other mechanical tool, may be used to "knock over" the nanostructures <NUM>, such that the long axes of the nanostructures become substantially aligned in a orientation that is parallel to the surface of growth substrate <NUM>. <FIG> illustrates a similar process, wherein a pattern of aligned nanostructures <NUM> may be formed on substrate <NUM> to a certain height. A roller <NUM> may be used to "knock over" the nanostructures, giving a substrate which contains aligned and uniformly distributed nanostructures, similar to a traditional aligned short-fiber composite ply. The loads may be transmitted among the nanostructures by shear lag stress transfer. For example, this process may occur in region <NUM> of the solid ring substrate shown in <FIG>, or following delamination of the nanostructures from the growth substrate.

For example, one or more support materials may be added to the set of aligned nanostructures (e.g., nanotube "forest") on the growth substrate, or other nanostructure supporting material, to form a solid or other integrally self-supporting structure. The addition of the support material, or precursor thereof, may harden, tackify, or otherwise strengthen the set of substantially aligned nanostructures, such that a solid structure comprising the aligned nanostructures is formed, for example, upon subsequent removal of the growth substrate.

In some cases, the support material may be a monomeric species and/or a polymer comprising cross-linking groups, such that polymerization and/or cross-linking of the polymers may form a hardened structure comprising the aligned nanostructures. The support material may be a metal or a metal powder such as a metal nanoparticles having diameter on the order of the diameter of the nanostructures or the spacing between the nanostructures on the substrate. The metal may be softened, sintered, or melted when added to the aligned nanostructures, such that cooling of the metal may form a metal structure comprising the aligned nanostructures. As used herein, an "integrally self-supporting structure" is defined as a non-solid structure having sufficient stability or rigidity to maintain its structural integrity (e.g., shape) without external support along surfaces of the structure. Solid and/or self- supporting structures comprising aligned nanostructures may be useful as substrate or other components for composite materials, as described herein.

In some cases, the disclosed methods may further comprise the act of annealing or densifying the nanostructures, prior to the act of removing the nanostructures.

In addition to growth of uniform nanostructures, two-dimensionally and three-dimensionally shaped nanostructure microstructures may also be manufactured by patterning the catalyst material on the growth substrate or by physically templating growth using mechanical forces. Lithographic patterning of the catalyst material may enable growth of nanostructure features having cross-sections as small as <NUM> microns or less. Patterned growth may also be achieved by contact printing of the catalyst material from a solution of block copolymer micelles. Nanostructures may be "grow-molded" into three-dimensionally shaped microstructures by confining growth to within the microfabricated cavity. For example, a microfabricated template may be clamped against the growth substrate and delaminated following nanostructure growth, releasing the free-standing nanostructure shapes.

As used herein, the term "nanotube" is given its ordinary meaning in the art and refers to a substantially cylindrical molecule or nanostructure comprising a fused network of primarily six-membered aromatic rings. In some cases, nanotubes may resemble a sheet of graphite formed into a seamless cylindrical structure. It should be understood that the nanotube may also comprise rings or lattice structures other than six- membered rings. Typically, at least one end of the nanotube may be capped, i.e., with a curved or nonplanar aromatic group. Nanotubes may have a diameter of the order of nanometers and a length on the order of millimeters, or, on the order of tenths of microns, resulting in an aspect ratio greater than <NUM>, <NUM>, <NUM>,<NUM>, or greater. In some cases, the nanotube is a carbon nanotube. The term "carbon nanotube" refers to nanotubes comprising primarily carbon atoms and includes single-walled nanotubes (SWNTs), double-walled CNTs (DWNTs), multi-walled nanotubes (MWNTs) (e.g., concentric carbon nanotubes), inorganic derivatives thereof, and the like. The carbon nanotube may be a single-walled carbon nanotube. In some cases, the carbon nanotube is a multi-walled carbon nanotube (e.g., a double-walled carbon nanotube). In some cases, the nanotube may have a diameter less than <NUM>, less than <NUM>, <NUM>, less than <NUM>, less than <NUM>, or, in some cases, less than <NUM>.

The nanotubes may have an average diameter of <NUM> or less, and may be arranged in composite articles as described herein.

The inorganic materials include semiconductor nanowires such as silicon (Si) nanowires, indium-gallium-arsenide (InGaAs) nanowires, and nanotubes comprising boron nitride (BN), silicon nitride (Si3N4), silicon carbide (SiC), dichalcogenides such as (WS<NUM>), oxides such as titanium dioxide (TiO<NUM>) and molybdenum trioxide (MoO<NUM>), and boron-carbon-nitrogen compositions such as BC<NUM>N<NUM> and BC<NUM>N.

As described herein, the nanostructures may be synthesized by contacting nanostructure precursor material with a catalyst material, for example, positioned on the surface of the growth substrate. The nanostructure precursor material may be a nanotube precursor material and may comprise one or more fluids, such as a hydrocarbon gas, hydrogen, argon, nitrogen, combinations thereof, and the like. Those of ordinary skill would be able to select the appropriate nanotube precursor material to produce a particular nanotube. For example, carbon nanotubes may be synthesized by reaction of a C<NUM>H<NUM>TH<NUM> mixture with a catalyst material, such as nanoparticles of Fe arranged on an Al<NUM>O<NUM> support. The synthesis of nanotubes is described herein by way of example only, and it should be understood that other nanostructures may be fabricated using methods described herein. For example, nanowires or other structures having high aspect ratio may be fabricated using growth substrates as described herein. For example, nanostructures having an aspect ratio of at least <NUM>:<NUM>, at least <NUM>:<NUM>, at least <NUM>:<NUM>, or, in some cases, at least <NUM>,<NUM>:<NUM>, may be fabricated. For example, the disclosed methods may be used to synthesize nanostructures having a diameter of less than <NUM> nanometers and a length of at least <NUM> micron. Those of ordinary skill in the art would be able to select the appropriate combination of nanotube precursor material, catalyst material, and set of conditions for the growth of a particular nanostructure.

The nanostructure precursor material may be introduced into the system and/or growth substrate by various methods. In some cases, the nanostructure precursor material may contact the surface of a fiber. For example, a flow of nanostructure precursor material may be introduced in a direction substantially perpendicular to the surface of the growth substrate, or, in a continuous method, in the direction of movement of the growth substrate through the system. The growth substrate may be moved at a particular along its axial direction, while a flow of nanostructure precursor material may impinge on the growth substrate in a direction perpendicular to growth substrate motion. In some cases, as the growth substrate is moved through the apparatus, the catalyst material may cause nucleation of a layer of aligned nanostructures, which may increase in thickness as the fiber moves through the growth apparatus.

In cases where the growth substrate comprises a plurality of fibers, such as bundles, weaves, tows, or other configurations where catalyst material may be located at an interior portion of the growth substrate, the growth substrate may comprise regularly- spaced fibers, wherein the flow of nanostructure precursor material can penetrate the space between the fibers, producing growth of aligned nanostructures essentially uniformly throughout the structure.

In some cases, the nanostructures may be primarily oriented radially around the fiber surface, wherein the long axes of the nanostructure may be oriented in a direction that is nonplanar with the surface of the growth substrate. In some cases, the nanostructures may grow in an ordered or disordered fashion on the fiber surface.

The catalyst material may be any material capable of catalyzing growth of nanotubes. The material may be selected to have high catalytic activity and optionally the ability to be regenerated after growth of a set of nanotubes. The material may also be selected to be compatible with the growth substrate such that the catalyst material may be deposited or otherwise formed on the surface of the growth substrate. For example, the catalyst material may be selected to have a suitable thermal expansion coefficient as the growth substrate to reduce or prevent delamination or cracks.

The catalyst material may be positioned on or in the surface of the growth substrate. In some cases, the catalyst material may be formed as a coating or pattern on the surface of the growth substrate, using known methods such as lithography. The growth substrate may be coated or patterned with the catalyst material by contacting at least a portion of the growth substrate with a solution, film, or tape comprising the catalyst material, or precursor thereof. In some cases, the growth substrate may be a fiber, which may be drawn through a liquid solution containing the catalyst materials, or precursors thereof, which may coat the surface of the fiber to provide growth sites for nanotubes. Such methods may be used to introduce the catalyst material to the growth substrate at various stages of a continuous process, such as in an initial stage or in later stages, where reapplication of a catalyst material to the growth substrate may be needed.

Materials suitable for use as the catalyst material include metals, for example, a Group <NUM>-<NUM> metal, a Group <NUM>-<NUM> metal, a Group <NUM>-<NUM> metal, or a combination of one or more of these. Elements from Group <NUM> that may be used may include, for example, iron, ruthenium, or osmium. Elements from Group <NUM> that may be used may include, for example, cobalt, rhenium, or indium. Elements from Group <NUM> that may be used may include, for example, nickel, palladium, or platinum. In some cases, the catalyst material is iron, cobalt, or nickel. For example, the catalyst material may be iron nanoparticles, or precursors thereof, arranged in a pattern on the surface of the growth substrate. The catalyst material may also be other metal-containing species, such as metal oxides, metal nitrides, etc. Those of ordinary skill in the art would be able to select the appropriate catalyst material to suit a particular application.

In some cases, nanotubes may be synthesized using the appropriate combination of nanotube precursors and/or catalyst materials, by delivering sequential exclusive reactant streams (e.g., comprising nanotube precursor materials), or by using a mixed reactant stream which causes growth of multiple types of nanostructures, and which is selective to the nature (e.g., elemental composition and size) of growth sites arranged on the substrates.

The catalyst material may be formed on the surface of the growth substrate using various methods, including chemical vapor deposition, for example. For example, a fiber may be drawn through a solution containing the catalyst material, or precursors there, and may exit from the solution with a coating of catalyst material on its surface. The coating may comprise growth sites such as metal nanoparticles (e.g., Fe, Co, and/or Ni) for growth of nanostructures such as carbon nanotubes from the surface of the fiber, or may be precursors to the formation of the growth sites. In some cases, the fiber may be continuously drawn through the solution containing the catalyst material, wherein, at the surface of the solution (e.g., a liquid-gas interface, or liquid-liquid interface), the catalyst material may be aggregated nanoparticles which may be drawn onto the surface of the fiber as it contacts the surface of the solution.

Other methods may be used to deposit the catalyst material on the growth substrate, such as Langmuir-Blodgett techniques, deposition from solutions of preformed nanoparticles such as ferrofluids, and deposition from solutions of metal salts which coat the substrate and decompose to form nanoparticles when heated (e.g., metal nitrates at <NUM>-<NUM>[°C). In some cases, block copolymers may be used to template the organization catalyst material on the growth substrate.

Substrates suitable for use include prepregs, polymer resins, dry weaves and tows, inorganic materials such as carbon (e.g., graphite), metals, alloys, intermetallics, metal oxides, metal nitrides, ceramics, and the like. In some cases, the substrate may be a fiber, tow of fibers, a weave, and the like. The substrate may further comprise a conducting material, such as conductive fibers, weaves, or nanostructures.

In some cases, the substrates as described herein may be prepregs, that is, a polymer material (e.g., thermoset or thermoplastic polymer) containing embedded, aligned, and/or interlaced (e.g., woven or braided) fibers such as carbon fibers. As used herein, the term "prepreg" refers to one or more layers of thermoset or thermoplastic resin containing embedded fibers, for example fibers of carbon, glass, silicon carbide, and the like. Thermoset materials include epoxy, rubber strengthened epoxy, BMI, PMK-<NUM>, polyesters, vinylesters, and the like, and preferred thermoplastic materials include polyamides, polyimides, polyarylene sulfide, polyetherimide, polyesterimides polyarylenes polysulfones polyethersulfones polyphenylene sulfide, polyetherimide, polypropylene, polyolefins, polyketones, polyetherketones, polyetherketoneketone, polyetheretherketones, polyester, and analogs and mixtures thereof. Typically, the prepreg includes fibers that are aligned and/or interlaced (woven or braided) and the prepregs are arranged such the fibers of many layers are not aligned with fibers of other layers, the arrangement being dictated by directional stiffness requirements of the article to be formed by the method. The fibers generally can not be stretched appreciably longitudinally, thus each layer can not be stretched appreciably in the direction along which its fibers are arranged. Exemplary prepregs include TORLON thermoplastic laminate, PEEK (polyether etherketone, Imperial Chemical Industries, PLC, England), PEKK (polyetherketone ketone, DuPont) thermoplastic, T800H/<NUM>-<NUM> thermoset from Toray (Japan), and AS4/<NUM>-<NUM> thermoset from Hercules (Magna, Utah).

The growth substrate may be any material capable of supporting catalyst materials and/or nanostructures as described herein. The growth substrate may be selected to be inert to and/or stable under sets of conditions used in a particular process, such as nanostructure growth conditions, nanostructure removal conditions, and the like. For example, the growth substrate may be stable under high temperature (e.g., up to <NUM>) CVD growth of carbon nanotubes. In some cases, the growth substrate may comprise alumina, silicon, carbon, a ceramic, or a metal. In some cases, the growth substrate comprises a substantially flat surface. In some cases, the growth substrate comprises a substantially nonplanar surface. For example, the growth substrate may be an optionally rotatable cylindrical substrate, such as a fiber, which may have a diameter ranging from <NUM> to <NUM>, for example. In some cases, the growth substrate may be a rigid ring (e.g., a cylindrical rigid ring), which may be continuously rotated during formation/removal of the nanotubes. In some cases, the growth substrate may comprise a flexible material, wherein the growth substrate may form a flexible ring or belt that may be placed on one or more rollers for continuous circulation through an apparatus, as described herein. The growth substrate may be a fiber comprising Al<NUM>O<NUM>, SiO<NUM>, or carbon. The growth substrate may comprise a layer, such as a transition metal oxide (Al<NUM>O<NUM>) layer, formed on surface of an underlying material, such as a metal or ceramic.

In some cases, the growth substrate may be hollow and/or porous. In some cases, the growth substrate is porous, such as a porous Al<NUM>O<NUM>. As used herein, a "porous" material is defined as a material having a sufficient number of pores or interstices such that the material is easily crossed or permeated by, for example, a fluid or mixture of fluids (e.g., liquids, gases). A porous growth substrate may improve the growth of nanotubes by advantageously facilitating the diffusion of reactant gases (e.g., nanotube precursor material) through the growth substrate to the catalyst material. <FIG> shows a schematic representation of a porous growth substrate, where substrate <NUM> contains pores or holes <NUM>, and nanostructures <NUM> grow on one surface of the substrate. The pores or holes enable uniform delivery of the reaction atmosphere across the area of the substrate surface. This is for example the atmosphere for pre-treatment of the substrate, for growth of nanostructures, or for reactivation of the catalyst.

<FIG> shows a growth substrate arranged on a component (e.g., roller) capable of supplying reactant materials to the growth substrate for the growth of nanostructures on a roller. The component may supply reactive and non-reactive chemical species for the growth of a layer of aligned nanostructures on the growth substrate, wherein chemical species may flow in a radial direction to the growth substrate. The growth substrate may be a hollow cylinder <NUM>, which may be porous to permit gas flow through its surface. A flow <NUM> of chemical species may be introduced axially along an input pipe <NUM> in fluid communication with the cylinder, and may be distributed and flowed in a radial direction <NUM> through the growth substrate to the surface. In some cases, the flow may supply nanostructure precursor materials, which may then interact with growth sites (e.g., catalytic material) on the surface of the growth substrate. Alternatively, catalyst material precursors may be supplied in the flow to form a layer of catalyst nanostructures on the surface of the growth substrate.

In some cases, the growth substrate comprises Al<NUM>O<NUM> or SiO<NUM> and the catalyst material comprises iron, cobalt, or nickel. In some cases, the growth substrate comprises Al<NUM>O<NUM> and the catalyst material comprises iron.

As used herein, a "nanostructure precursor material" refers to any material or mixture of materials that may be reacted to form a nanostructure under the appropriate set of conditions. The nanostructure precursor material may comprise a carbon- containing species (e.g., hydrocarbons such as C<NUM>H<NUM> and CH<NUM>, alcohols, etc.), one or more fluids (e.g., gases such as H<NUM>, O<NUM>, helium, argon, nitrogen, etc.), or other chemical species that may facilitate formation of nanostructures. One or more binding materials or support materials may be used or added. The binding or support materials may be polymer materials, fibers, metals, or other materials described herein. Polymer materials for use as binding materials and/or support materials, as described herein, may be any material compatible with nanostructures. For example, the polymer material may be selected to uniformly "wet" the nanostructures and/or to bind one or more substrates. In some cases, the polymer material may be selected to have a particular viscosity, such as <NUM>,<NUM> cPs or lower, <NUM>,<NUM> cPs or lower, <NUM>,<NUM> cPs or lower, <NUM>,<NUM> cPs or lower, <NUM> cPs or lower, <NUM> cPs or lower, or, <NUM> cPs or lower. The polymer material may be selected to have a viscosity between <NUM>-<NUM> cPs. In some cases, the polymer material may be a thermoset or thermoplastic. In some cases, the polymer material may optionally comprise a conducting material, including conductive fibers, weaves, or nanostructures.

Examples of thermosets include Microchem SU-<NUM> (UV curing epoxy, grades from <NUM> to <NUM>, and viscosities ranging from <NUM> cPs to <NUM>,<NUM> cPs), Buehler Epothin (low viscosity, - <NUM> cPs, room temperature curing epoxy), West Systems <NUM> + <NUM> Hardener (low viscosity, ~<NUM> cPs, room temperature curing epoxy), Loctite Hysol <NUM> C (<NUM>-min curing conductive epoxy, viscosity <NUM>,<NUM> - <NUM>,000cPs), Hexcel RTM6 (resin transfer molding epoxy, viscosity during process ~<NUM> cPs), Hexcel HexFlow VRM <NUM> (structural VARTM or vacuum assisted resin transfer molding epoxy, viscosity during process ~<NUM> cPs). Examples of thermoplastic include polystyrene, or Microchem PMMA (UV curing thermoplastic, grades ranging from <NUM> cPs to ~<NUM>,<NUM> cPs). The polymer material may be PMMA, EpoThin, WestSystems EPON, RTM6, VRM34, <NUM>-<NUM>, SU8, or Hysol1C.

The following examples illustrate certain processes and articles herein disclosed which are applicable to or illustrative of elements of the claimed invention. It should be understood that the processes described herein may be modified and/or scaled for operation in a large batch or a continuous fashion, as known to those of ordinary skill in the art.

The following example describes an exemplary process for growing layers of aligned carbon nanotubes on a substrate. A patterned catalyst film of <NUM>/<NUM> Fe/Al<NUM>O<NUM> was deposited on a plain (<NUM>) <NUM>" silicon wafer (p-type, <NUM>-<NUM> Q-cm, Silicon Quest International, which was cleaned using a standard "piranha" (<NUM>:<NUM><NUM>SO<NUM>:H<NUM>O<NUM>) solution) by e-beam evaporation in a single pump-down cycle using a Temescal VES-<NUM> with a FDC-<NUM> Film Deposition Controller. The catalyst pattern was fabricated by lift-off of a <NUM> layer of image-reversal photoresist (AZ-5214E), which was patterned by photolithography. The catalyst was deposited over the entire wafer surface, and the areas of catalyst that were deposited on the photoresist were removed by soaking in acetone for <NUM> minutes, with mild sonication. The film thickness of the catalyst was measured during deposition using a quartz crystal monitor and was later confirmed by Rutherford backscattering spectrometry (RBS).

CNT growth was performed in a single-zone atmospheric pressure quartz tube furnace (Lindberg), having an inside diameter of <NUM> and a <NUM> long heating zone, using flows of argon (Ar, <NUM>%, Airgas), ethylene (C<NUM>H<NUM>, <NUM>%, Airgas), and hydrogen (H<NUM>, <NUM>%, BOC). The furnace temperature was ramped to the setpoint temperature in <NUM> minutes and held for an additional <NUM> minutes under <NUM> sccm Ar. The C<NUM>H<NUM>/H<NUM> Ar mixture was maintained for the growth period of <NUM>-<NUM> minutes. Finally, the H<NUM> and C<NUM>H<NUM> flows were discontinued, and <NUM> sccm Ar is maintained for <NUM> more minutes to displace the reactant gases from the tube, before being reduced to a trickle while the furnace cools to below <NUM>.

Carbon nanotube structures were grown from the FeZAl2O3 film processed in <NUM>/<NUM>/<NUM> sccm C<NUM>H<NUM>/H<NUM>/Ar, at <NUM>. As shown in <FIG>, the carbon nanotubes are oriented primarily perpendicular to the substrate and are isolated or are clustered in "bundles" as large as <NUM> diameter, in which the carbon nanotubes are held closely together by surface forces. <FIG> shows an oblique view (stage tilted <NUM>°) SEM image of an aligned CNT forest, approximately <NUM> high, grown in <NUM> minutes from <NUM>/<NUM>/<NUM> sccm C<NUM>H<NUM>/H<NUM>/argon (scale <NUM>), while <FIG> shows alignment of carbon nanotubes within the film, viewed from the side (scale <NUM>). Alternatively, a carrier gas of He is used instead of Ar, and the furnace is ramped to the setpoint (growth) temperature and stabilized under a flow of <NUM>/<NUM> sccm He/H<NUM>, and a flow of <NUM>/<NUM>/<NUM> sccm C<NUM>H<NUM>/He/H<NUM> is introduced during the growth period.

<FIG> show carbon nanotube microstructures grown from an Al<NUM>O<NUM> substrate having lithographically-patterned Fe catalyst sites. Carbon nanotube structures having identical cross-sections can be grown in large arrays and complex shapes can be defined. <FIG> shows an array of nanotube "pillars" approximately <NUM> high, grown in <NUM> minutes (scale <NUM>), while <FIG> shows a complex pattern of carbon nanotubes which grew taller near its center, and having sharp features reproduced from high-resolution lithography mask (scale <NUM>).

<FIG> shows the HRTEM examination of carbon nanotubes, which were primarily multi-walled and tubular. The carbon nanotubes averaged approximately <NUM> OD and <NUM> ID, and most have <NUM>-<NUM> concentric parallel walls. <FIG> shows the final thickness of an aligned carbon nanotube film grown at different temperatures, for equal growth times of <NUM> minutes with <NUM>/<NUM>/<NUM> sccm C<NUM>H<NUM>/H<NUM>/Ar. <FIG> shows the final thickness of an aligned CNT film grown at different C2H4 flows (in addition to <NUM>/<NUM> sccm H<NUM>/Ar), for equal growth times of <NUM> minutes at <NUM>. As shown in <FIG>, the growth rate and thickness of the carbon nanotube film can be adjusted by controlling the reaction temperature (<FIG>), or by adjusting the concentration Of C<NUM>H<NUM> in the feedstock (<FIG>). Adjustment of the catalyst particle size, catalyst material, reactants and/or additive species, flow sequence, temperature, pressure, and other parameters, by methods known to those skilled in the art can suitably control the morphology (diameter, crystallinity) and density of aligned CNTs within such layers.

The following examples describes the production of ceramic fibers containing carbon nanotubes on the surface of the fibers. Fiber strands were cut from a commercially-available (McMaster-Carr) aluminum oxide (Al<NUM>O<NUM>) fiber cloth and soaked for five minutes in a <NUM> solution of Fe(NO<NUM>)<NUM> • <NUM><NUM>O in isopropanol (prepared by stirring and sonication). The fiber strands were then allowed to dry in air. <FIG> shows SEM images of the Al<NUM>O<NUM> fibers loaded with the iron catalyst material on a (a) <NUM> micron and (b) <NUM> micron scale. The Al<NUM>O<NUM> fibers were about <NUM> in diameter, each strand comprising several hundred fibers. Carbon nanotube growth was performed using a single-zone atmospheric pressure quartz tube furnace (Lindberg) having an inside diameter of <NUM> and a <NUM> long heating zone. Flows of Ar (<NUM>%, Airgas), C<NUM>H<NUM> (<NUM>%, Airgas), and H<NUM> (<NUM>%, BOC) were measured using manual needle-valve rotameters. The furnace temperature was held at <NUM>, with <NUM>/<NUM>/<NUM> sccm C<NUM>H<NUM>/H<NUM>/Ar.

Two processes were studied. First, the Al<NUM>O<NUM> fibers were processed in a "batch" CVD sequence by placing the fibers in the furnace with a mixture of C<NUM>H<NUM>/H<NUM>/Ar gas, and then heating the furnace to the nanotube growth temperature. Aligned coatings of carbon nanotubes were then formed on the surfaces of the Al<NUM>O<NUM> fibers. In an alternative process (e.g., "rapid heating" sequence), the Al<NUM>O<NUM> fibers were rapidly introduced to the hot zone of the furnace after the furnace was heated to the nanotube growth temperature. After <NUM>-<NUM> minutes, the C<NUM>H<NUM>/H<NUM>/Ar growth mixture was then introduced. The resulting fibers from both processes are shown in <FIG>.

<FIG> shows an SEM image of the carbon nanotube-coated Al<NUM>O<NUM> fibers (<NUM> solution, <NUM> micron scale) after <NUM> minutes of growth time and <NUM>/<NUM>/200sccm C<NUM>H<NUM>/H<NUM>/Ar. <FIG> shows an SEM image of the carbon nanotube alignment within the carbon nanotube coating (<NUM> micron scale). <FIG> shows SEM images of bundles the carbon nanotube-coated Al<NUM>O<NUM> fibers at (a) 50x and (b) 250x magnification, indicating that growth of aligned nanotubes occurred on fibers throughout the tow, and far beneath the outer surface of the tow. <FIG> shows SEM images of the coated fibers, coated by a in a (a) <NUM> Fe solution, (b) <NUM> Fe solution, (c) <NUM> Fe solution. <FIG> shows an SEM image of the coated fibers formed by the rapid heating CVD sequence, in a <NUM> Fe solution. As shown in <FIG>, an increase in coverage of the aligned carbon nanotube on Al<NUM>O<NUM> fibers was observed for fibers which were soaked in higher-concentration Fe solution and/or produced by the rapid heating CVD sequence.

As demonstrated by <FIG>, an aligned growth morphology of carbon nanotubes was achieved, and the residence time (feed rate) of fibers in the hot zone of the furnace can be chosen to give the desired thickness of CNT layer on the fiber surfaces. The uniformity of CNT coating may be affected by the concentration of the Fe solution, yet may also be affected by uneven evaporation fronts in batch soaking of the fibers in the solution. Uniform coatings of catalyst precursors can be achieved by continuous withdrawal of the substrate from the catalyst or catalyst precursor solution.

The following example describes the production of composite thin films containing vertically-aligned carbon nanotubes. A pattern of rectangular "pillars" containing carbon nanotubes was grown on a silicon wafer, according to the process described in Example <NUM>. The carbon nanotubes were vertically-aligned and substantially perpendicular to the substrate, and were held together in the form of pillars by surface forces. By adjusting the either the concentration of C<NUM>H<NUM> in the reaction chamber or the reaction temperature, it was possible to control the growth rate and height of the carbon nanotube pillars. In this example, the carbon nanotube height was measured to be <NUM>.

The carbon nanotubes on the silicon wafer were then combined with a second substrate to form a composite thin film. A fast-curing (e.g., <NUM> minute) room-temperature conductive epoxy was deposited on a glass substrate (e.g., the "second" substrate) in the form of a thin film having a thickness approximately the same as the height as the carbon nanotubes. The silicon wafer containing the carbon nanotube pattern was then placed on the glass substrate, such that the carbon nanotube and the conductive epoxy contacted each other, and a <NUM> weight was applied on the assembly. The assembly was kept at ambient temperature and humidity, allowing the conductive epoxy to cure over <NUM> hours. Capillary action, aided by the mechanical pressure exerted by the weight, allowed the epoxy to penetrate into the carbon nanotube-pillars. After <NUM>, the epoxy was completely cured. The adhesion between the epoxy and the carbon nanotubes was sufficient to allow the removal of the silicon wafer by mechanical means. <FIG> shows an SEM image of an arrangement of aligned carbon nanotube pillars embedded in an epoxy matrix, shows the effective wetting of the pillars by the epoxy. <FIG> shows a closer view of an embedded carbon nanotube pillar, showing the nanotube/epoxy interface.

Alternatively, a submersion process may also be used to effectively wet pillars and dense "forests" of carbon nanotubes, wherein capillary action can aid penetration of the epoxy into the carbon nanotube forest. <FIG> show SEM images of epoxy penetrated by carbon nanotube "forests" by a submersion process, wherein the effectiveness of carbon nanotube wetting was exhibited. As shown in cross-sectional view of the nanotube/epoxy assembly in <FIG>, the epoxy polymer fully penetrated the thickness of the forest and the CNT alignment was maintained. <FIG> shows an SEM image of a carbon nanotube/SU-<NUM> composite with ~<NUM>% volume fraction, wherein the wetting was effective and no voids were observed, and <FIG> shows a closer view of the composite. <FIG> shows a <NUM>% volume fraction carbon nanotube/RTM <NUM> composite, wherein the effectiveness of the submersion method for wetting can be observed, even at higher volume fractions, and <FIG> shows a closer view of the composite.

The following example describes the transfer of a carbon nanotube forest to a receiving substrate, and the production of "nanostitched" composite structures.

A carbon nanotube "forest" was grown on a silicon wafer to a height of ~<NUM> using the method described in Example <NUM>. <FIG> show SEM images of the carbon nanotubes, which have been transplanted from that substrate to a prepreg using mechanical means, and retention of carbon nanotube alignment was observed upon transfer.

To produce "nanostitched" composite structures, a rectangular piece of a commercially available graphite fiber/epoxy prepreg (AS4/<NUM>-<NUM> or IM7/<NUM>-<NUM>) was cut, and the CNT forest was transplanted to the surface of the prepreg using mechanical means, i.e., was transferred from the growth substrate to a receiving substrate, as illustrated in <FIG>. A caul plate was placed on top of the carbon nanotube "forest" and pressure was then applied in the form of a <NUM> weight placed on the silicon wafer. The assembly was heated (or brought to room temperature) until the epoxy on the surface of the prepreg softened. The mechanical pressure and the softening of the epoxy allowed the carbon nanotubes to penetrate into the epoxy of the prepreg. The depth of nanotube penetration was controlled by adjusting the temperature of the surface and/or the magnitude of weight applied to the carbon nanotube substrate. When the CNTs were sufficiently embedded in the prepreg, the weight was removed and the epoxy was fully cured. <FIG> shows the resulting prepreg containing a forest of carbon nanotubes on its surface, at (a) <NUM> micron and (b) <NUM> micron scales. This configuration can be used for the creation of a reinforced multilayered composite material, as described herein.

Alternatively, a carbon nanotube layer was placed between two plies of graphite/epoxy prepregs. The carbon nanotube forest was transplanted to the surface of one of the two prepreg plies, and the second ply was added on top of the forest, as illustrated schematically in <FIG>. The assembly was fully cured using an autoclave, and the resulting hybrid composite is shown in <FIG>, at (a) <NUM> micron and (b) <NUM> micron scales. As seen in <FIG>, the carbon nanotubes in the interface penetrated into the prepreg ply ~<NUM>-<NUM> (on the same order of the carbon fiber diameter), depending on the region.

Double-cantilever beam specimens containing an aligned CNT layer in the midplane fabricated using the process described above were subjected to Mode I fracture tests. The results were compared with those of unreinforced composites. As shown in <FIG>, the carbon nanotube was shown to increase the fracture toughness of the composite by <NUM>%, i.e., to <NUM>%.

<FIG> show SEM images of the carbon nanotube/graphite/epoxy hybrid composite on (a) <NUM> micron and (b) <NUM> micron scales.

The following example describes the production of a woven, layered composite structure containing carbon nanotubes, alumina fiber, and epoxy. A carbon nanotube forest was grown to a height of <NUM>, according to the method described in Example <NUM>. After growing the carbon nanotubes on the surface of the alumina fibers, the CNT/alumina cloth plies were submerged in Buehler's EpoThin epoxy and stacked to create a hybrid composite laminate. Vacuum-assisted curing was used to cure the composite structure, as illustrated in <FIG>. The laminate was placed on a vacuum table, and a layer of non-porous Teflon was placed on top, followed by a caul plate of the same dimensions of the laminate (the non-porous Teflon was used to avoid the laminate sticking to the caul plate). Layers of porous Teflon and bleeding paper were placed on top of the assembly to remove the excess of epoxy during the curing process. A sheet of glass fiber was placed over the vacuum table to cover the assembly as well as the vacuum table, to ensure uniform distribution of the vacuum. Finally, a vacuum bag was used to enclose the assembly and a pressure of <NUM> psi was applied during the curing process.

A photograph of the resulting CNT/alumina/epoxy nanoengineered laminate is shown in <FIG>. The excess epoxy was effectively eliminated from the nanoengineered composite laminate by applying pressure (<NUM> psi) during the curing process, and a sample was then cut with a fret-saw. An illustrative sample is shown by the photograph in <FIG>.

In an additional example, similar composite structures were manufactured with alumina cloth. Carbon nanotubes grown on the surface of fibers using the process described herein. Short beam shear (SBS) tests were applied to intralaminar specimens to determine the interlaminar shear strength. (<FIG>) The results were compared with those of similar composites lacking the carbon nanotubes, i.e., "unreinforced" composites, and are shown in <FIG>. The CNT architecture increased the interlaminar shear strength of the composite by <NUM>%.

Also, a composite structure containing carbon nanotubes, alumina fiber, and epoxy was manufactured following the steps described in Example <NUM>. <FIG> shows an SEM image of the carbon nanotube/alumina/epoxy hybrid composite on a <NUM> micron scale. As shown by <FIG>, the epoxy fully penetrates and wets the carbon nanotubes and alumina fibers. The uniform distribution of the fibers can also be observed. The electrical conductivity of the composite structure containing carbon nanotubes, alumina fiber, and epoxy was then studied. <FIG> shows, schematically, the experimental setup for the electrical conductivity tests, where the composite was placed between two silver paint electrodes and its electrical properties were measures. <FIG> shows the results from the electrical resistivity measurements.

In the following example, a set of carbon nanotubes was grown, as described herein, on a graphite (e.g., carbon) fiber and was utilized in the fabrication of various composite structures. As shown in the SEM image in <FIG>, carbon nanotubes were grown on a graphite fiber wherein the long axes of the carbon nanotubes are oriented perpendicular to the fiber surface.

Nanostructure "pillars" containing carbon nanotubes and epoxy were fabricated using the submersion method. <FIG> shows SEM images of carbon nanotube/epoxy pillars fully wet and with their shapes and CNT alignment maintained.

The following example describes the production of carbon nanotubes using a continuous process as described herein.

<FIG> shows real-time measurement of the thickness of a film of aligned carbon nanotubes grown on a growth substrate by cycling the atmosphere surrounding the growth substrate between a reactive, C<NUM>H<NUM>/H<NUM> atmosphere and an inert, H<NUM> atmosphere, where the marks placed along the left edge of the image indicate the interfaces between consecutive layers. The film grew upon exposure of the growth substrate, coated with Fe catalyst and Al<NUM>O<NUM> supporting layer, was exposed to C<NUM>H<NUM>/H<NUM>, and growth was paused when the substrate is exposed to H<NUM> alone This was replicated in a continuous fashion using a rotating cylindrical substrate where the growth zone was maintained at temperature T in an atmosphere of C<NUM>H<NUM>/H<NUM> ("condition set <NUM>") and the delamination and pre-treatment zones were maintained at a different temperature ("condition set <NUM>"). During this stage of continuous operation, where the same catalyst was recycled many times, the intermediate zones was maintained at condition set <NUM> and the catalyst could be removed and replaced when it was no longer suitably active for production of nanostructures. <FIG> shows a scanning electron micrograph of the carbon nanotube film grown by this process, where the marks placed along the left edge of the image indicate the interfaces between consecutive layers. The layers can be cleanly separated as shown in <FIG>, wherein each layer represents the growth of carbon nanotubes per interval.

<FIG> shows AFM images of the surface topography of an Fe/Al<NUM>O<NUM> (<NUM>/<NUM>) supported catalyst film on a silicon substrate (a) after deposition but before any thermal or chemical treatment, (b) after heating in argon atmosphere and subsequent cooling, (c) after heating in argon/H<NUM> atmosphere and subsequent cooling. <FIG> may indicate that pretreating the catalyst-coated substrate in a reducing (H<NUM>-containing) atmosphere may aid in formation of Fe nanoparticles which are growth sites for carbon nanotubes when C<NUM>H<NUM> is later added to the reaction atmosphere.

Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to "A and/or B," when used in conjunction with open-ended language such as "comprising" can refer to A without B (optionally including elements other than B); to B without A (optionally including elements other than A); or to both A and B (optionally including other elements); etc..

Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements.

Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); or to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc..

Claim 1:
A method of forming a composite article, comprising:
providing a first and a second substrate, each having a joining surface;
arranging a set of substantially aligned nanostructures on or in the joining surface of at least one of the first and second substrates such that the nanostructures are dispersed uniformly on or in at least <NUM>% of the joining surface and the long axes of the nanostructures are non-parallel to the joining surface; and
binding the first and second substrates to each other via their respective joining surfaces to form an interface of the substrates such that at least a portion of the lengths of the nanostructures penetrate the joining surface of at least one of the first and second substrates, wherein the interface comprises the set of substantially aligned nanostructures;
wherein the first and second substrates are a first and second prepreg composite ply, respectively, and the method further comprises the step of:
curing the prepreg to bind the nanostructures and prepreg composite plies.