bluuebunny/crossref_metadata_2025 huggingface dataset:
X‐Ray and Neutron Diffuse Scattering Measurements
Authors: Ice Gene E. , Robertson James L. , Sparks Cullie J.
Published: October 2003

Diffuse scattering from crystalline solid solutions is used to measure local compositional order among the atoms, dynamic displacements (phonons), and mean species‐dependent static displacements. In locally ordered alloys, fluctuations of composition and interatomic distances break the long‐range symmetry of the crystal within local regions and contribute to the total energy of the alloy. Local ordering can be a precursor to a lower temperature equilibrium structure that may be unattainable because of slow atomic diffusion. In addition to local atomic correlations, neutron diffuse scattering methods can be used to study the local short‐range correlations of the magnetic moments. Interstitial defects, as opposed to the substitutional disorder defects described above, also disrupt the long‐range periodicity of a crystalline material and give rise to diffusely scattered x rays, neutrons, and electrons.

This article will concentrate on the use of diffuse x‐ray and neutron scattering from single crystals to measure local chemical correlations and chemically specific static displacements. Particular emphasis is placed on the use of resonant (anomalous) x‐ray techniques to extract information on atomic size from binary solid solutions with short‐range order. Here the alloys have a well‐defined average lattice but have local fluctuations in composition and displacements from the average lattice. In stoichiometric crystals with long‐range periodicity, sharp superlattice Bragg reflections appear. If the compositional order is correlated only over short distances, the superlattice reflections are so broadened that measurements throughout a symmetry related volume in reciprocal space are required to determine its distribution. In addition, the displacement of the atom pairs (e.g., the A‐A, A‐B, and B‐B pairs in a binary alloy) from the sites of the average lattice because of different atom sizes also contributes to the distribution of this diffuse scattering. By separating this diffuse intensity into its component parts—that associated with the chemical preference for A‐A, A‐B, and B‐B pairs for the various near‐neighbor shells and that associated with the static and dynamic displacements of the atoms from the sites of the average lattice—we are able to recover pair correlation probabilities for the three kinds of pairs in a binary alloy. The interpretation of diffuse scattering associated with dynamic displacements of atoms from their average crystal sites are discussed only briefly in this article.
X‐Ray Diffraction Techniques for Liquid Surfaces and Monomolecular Layers
Authors: Vaknin David
Published: October 2003

X‐ray and neutron scattering techniques are probably the most effective tools employed to determine the structure of liquid interfaces on molecular‐length scales. These are not different in principle from conventional x‐ray diffraction techniques that are usually applied to three‐dimensional crystals, liquids, solid surfaces etc. However, special diffractometers that enable scattering from fixed horizontal surfaces are required to carry out the experiments. Indeed, systematic studies of liquid surfaces had not begun until the introduction of the first liquid surface reflectometer.

A basic property of a liquid‐gas interface is the length scale over which the molecular density changes from the bulk value to that of the homogeneous gaseous medium. Molecular size and capillary waves, which depend on surface tension and gravity, are among the most important factors that shape the density profile across the interface and the planar correlations. In some instances the topmost layers of liquids are packed differently than in the bulk, giving rise to layering phenomena at the interface. Monolayers of compounds different than the liquid can be spread at the gas‐liquid interface, and are termed Langmuir monolayers. The spread compound might “wet” the liquid surface to form a film of homogeneous thickness or cluster to form an inhomogeneous rough surface. The x‐ray reflectivity (XR) technique allows one to determine the electron density across such interfaces, from which the molecular density and the total thickness can be extracted. The grazing angle diffraction (GID) technique is commonly used to determine lateral arrangements and correlations of the topmost layers at interfaces. GID is especially efficient in cases where surface crystallization of the liquid or spread monolayers occurs. Both techniques (XR and GID) provide structural information that is averaged over macroscopic areas, in contrast to scanning probe microscopies (SPMs), where local arrangements are probed. For an inhomogeneous interface, the reflectivity is an incoherent sum of reflectivities, accompanied by strong diffuse scattering, which, in general, is difficult to interpret definitively and often requires complementary techniques to support the x‐ray analysis. Therefore, preparation of well‐defined homogeneous interfaces is a key to a more definitive and straightforward interpretation.
X‐Ray Magnetic Circular Dichroism
Authors: Lang J.C.
Published: October 2003

X‐ray magnetic circular dichroism (XMCD) is a measure of the difference in the absorption coefficient, with the helicity of incident circularly polarized light parallel and antiparallel to the local magnetization direction of the absorbing material. These measurements are typically made at x‐ray energies spanning an absorption edge, where a deep atomic core electron is photoexited into the valence band. Because the binding energy of these core electrons is associated with specific elements, XMCD can be used to separately measure the magnetic contributions from individual constituents in a complex material, by tuning the incident beam energy to a specific edge. Furthermore, different absorption edges of the same element provide information on the magnetic contributions of different kinds of valence electrons within a single element.

XMCD measurements yield two basic types of magnetic information, both of which are specific to the element and orbital determined by the choice of measured absorption edge. First, the strength of the dichroic signal is proportional to the projection of the magnetic moment along the incident x‐ray beam direction. Thus, the signal can be used to determine magnetization direction for a sample in remanence or changes in the sample magnetization upon varying the applied magnetic field or temperature. Secondly, XMCD can be used to separate the orbital and spin contributions to the magnetic moment. This is possible through sum rules.

This article concentrate on the techniques employed in the hard x‐ray regime, but considerable mention will be made of soft x‐ray results and techniques because of the fundamental importance in magnetism of the final states probed by edges in this energy regime. Emphasis is given to the methods used for the collection of XMCD spectra rather than to detailed analysis of specific features in the XMCD spectra of a particular edge.
Surface X‐Ray Diffraction
Authors: Robinson I.K.
Published: October 2003

Surface x‐ray diffraction allows the determination of atomic structures of ordered crystal surfaces in an analogous way to x‐ray crystallography for the determination of three‐dimensional crystal structures. In doing this, crystallographic parameters such as lattice constants and Debye‐Waller factors (thermal vibration amplitudes) are also accessed, so surface x‐ray diffraction should be considered as a valid method for measuring these quantities too. Surface x‐ray diffraction also probes surface morphological properties, such as roughness and facet formation, and allows the investigation of their thermodynamic and kinetic aspects, such as the study of phase transitions in surfaces.

Because x rays probe deep inside matter, buried interfaces can be treated in exactly the same manner as surfaces, so throughout this unit the wordssurfaceandinterfaceare used synonymously. In fact, some of the best applications of the method are for buried interfaces, where complementary electron‐based probes such as low‐energy electron diffraction and reflection high‐energy electron diffraction cannot reach.

Surface x‐ray diffraction is not a laboratory technique. While there are one or two exceptions of installations in individual laboratories, the majority are associated with national or international facilities. Even the very early experiments used synchrotron radiation. By now, facility‐based science is already rather common and will become more so in the future, as it has considerable economies of scale and advantages of centralized operational safety. The practice of surface x‐ray diffraction should necessarily be considered as a facility‐based operation, and it will be assumed that the reader will have access as a “user” to one of these facilities. This is usually handled by the submission of a proposal to be judged on the importance of the science to be carried out. Access is then usually free of charge.

Because surface x‐ray diffraction is facility based, it is not a technique for which one can purchase the equipment piecemeal from a vendor. Every surface x‐ray diffraction installation is slightly different, but most were derived from and are based on the description that follows, which is the X16A facility of the National Synchrotron Light Source (NSLS).Others use basically the same control and analysis programs and procedures as those described here.
Electron Techniques
Authors: Fultz Brent
Published: October 2003

This section describes how electrons are used to probe the microstructures of materials. These methods are arguably the most powerful and flexible set of tools available for materials characterization. For the characterization of structures internal to materials, electron beam methods provide capabilities for determining crystal structure, crystal shapes and orientations, defects within the crystals, and the distribution of atoms within these individual crystals. For characterizing surfaces, electron methods can determine structure and chemistry at the level of the atomic monolayer.

The methods in this category use electrons with kinetic energies spanning the range from 1 to 1,000,000 eV.

Electron scattering from a material can be either elastic or inelastic. In general, elastic scattering is used for imaging measurements, whereas inelastic scattering provides for spectroscopy. (Electron beam techniques are enormously versatile, however, so there are many exceptions to this generality.).

The articles are this category enumerate some requirements for sample preparation, but it is remarkable that any one of these techniques permits studies on a large variety of samples. All classes of materials (metals, ceramics, polymers, and composites) have been studied by all of these electron techniques. Except for some problems with the lightest (or heaviest) elements in the periodic table, the electron beam techniques have few compositional limitations.
Transmission Electron Microscopy
Authors: Howe James M. , Fultz Brent
Published: October 2003

Transmission electron microscopy (TEM) is the premier tool for understanding the internal microstructure of materials at the nanometer level. Although x‐ray diffraction techniques generally provide better quantitative information than electron diffraction techniques, electrons have an important advantage over x rays in that they can be focused using electromagnetic lenses. This allows one to obtain real‐space images of materials with resolutions on the order of a few tenths to a few nanometers, depending on the imaging conditions, and simultaneously obtain diffraction information from specific regions in the images (e.g., small precipitates) as small as 1 nm. Variations in the intensity of electron scattering across a thin specimen can be used to image strain fields, defects such as dislocations and second‐phase particles, and even atomic columns in materials under certain imaging conditions. Transmission electron microscopy is such a powerful tool for the characterization of materials that some microstructural features are defined in terms of their visibility in TEM images.

In addition to diffraction and imaging, the high‐energy electrons (usually in the range of 100 to 400 keV of kinetic energy) in TEM cause electronic excitations of the atoms in the specimen. Two important spectroscopic techniques make use of these excitations by incorporating suitable detectors into the transmission electron microscope, energy‐dispersive x‐ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS).

A fully equipped transmission electron microscope has the capability to record the variations in image intensity across the specimen using mass thickness or diffraction contrast techniques, to reveal the atomic structure of materials using high‐resolution (phase‐contrast) imaging or
Z
‐contrast (incoherent) imaging, to obtain electron diffraction patterns from small areas of the specimen using a selected‐area aperture or a focused electron probe, and to perform EELS and EDS measurements with a small probe. Additional lenses can be installed in conjunction with an EELS spectrometer to create an energy filter, enabling one to form energy‐filtered TEM images. These images enable mapping of the chemical composition of a specimen with nanometer spatial resolution.

In addition to the main techniques of (1) conventional imaging, (2) phase‐contrast imaging, (3)
Z
‐contrast imaging, (4) electron diffraction, (5) EDS, and (6) EELS, in TEM many other analyses are possible.
Scanning Tunneling Microscopy
Authors: Salmeron Miquel
Published: October 2003

Scanning tunneling microscopy (STM) is a technique for the determination of the structure of surfaces, with spatial resolution on the angstrom scale. In an oversimplified description, STM allows imaging of the surface of conductive materials down to the atomic level.

The technique is based on the measurement and control of the current of electrons tunneling between a sharp stylus (hereafter called the tip) and the sample surface. During imaging, the tip is separated a few angstroms (3 to 10 Å) from the surface, while it is being rastered with the help of piezoelectric transducers. The area scanned is tens to thousands of angstroms on a side. STM has the advantage over other microscopies that its operation does not require any special environmental conditions. Imaging can be performed in vacuum, at high pressures (including air), and in liquids. The choice of the environment is determined mostly by the requirements of the sample and its surface condition.

Acquisition of STM images is relatively simple with modern instruments. Most of the experimental time is spent on sample preparation and tip conditioning in the appropriate environment (ultrahigh vacuum, electrochemical cell, or controlled atmosphere). Tip conditioning and noise reduction can sometimes add considerable time, depending on factors such as the nature of the experiment and reactivity of the sample. This time depends also on the type of information being sought.

In considering the ultimate resolution obtainable with the STM, it is important to consider the role of tip geometry. On flat parts of the sample, where one tip atom is responsible for the tunneling, STM reaches its maximum performance. On rough surfaces, however, the tunneling point on the tip apex changes as it moves over sharp corners and changing slopes. The image is then a convolution of the tip and surface shapes, and the final resolution is determined by the tip radius and profile. STM is thus not the best technique to probe, for example, highly corrugated a patterned surfaces, and porous materials.
Energy‐Dispersive Spectrometry
Authors: Newbury Dale E.
Published: October 2003

Energy‐dispersive x‐ray spectrometry (EDS) is a technique for measuring the intensity of x‐ray emission as a function of the energy of the x‐ray photons. The excitation source for the x‐rays can be energetic electrons, photons, or ions, and the target can be solid, liquid, or gas, although solid targets are the norm in virtually all materials science applications. The measured x‐ray intensity can be related to the concentration (i.e., mass or atomic fraction) for each element present by performing physical/empirical matrix corrections to account for the interelement modification of the generated x radiation caused by (1) primary radiation stopping power and ionization effects, (2) attenuation of secondary characteristic x‐rays during their passage through matter, and (3) any inefficiencies in detection. In this article, various aspects of the process of obtaining high‐quality x‐ray spectra, the interpretation of spectra, and the accurate extraction of x‐ray intensities from spectra are considered.

Materials analysis techniques that employ EDS include the following.

Electron excitation: (1) electron probe x‐ray microanalysis (EPMA)/analytical scanning electron microscopy (ASEM), where EDS complements wavelength‐dispersive x‐ray spectroscopy (WDS); (2) analytical electron microscopy (AEM).

Photon excitation:X‐ray fluorescence (XRF).

Ion excitation:particle‐induced x‐ray emission (PIXE).

This article will concentrate on EDS performed in electron‐beam instruments. The general principles of EDS x‐ray detection, processing, display, and spectral manipulation are similar for all analytical techniques regardless of the excitation source. The procedures for quantitative analysis depend in detail on the excitation process. Quantitative x‐ray microanalysis by electron excitation is considered in detail in the section on Electron Probe Microanalysis. Those aspects of quantitative x‐ray microanalysis that are particular to EDS spectral measurement are considered.
Trace Element Accelerator Mass Spectrometry
Authors: McDaniel Floyd Del
Published: October 2003

Accelerator mass spectrometry is a relatively new analytical technique that is being used in over 40 laboratories worldwide for the measurements of cosmogenic long‐lived radioisotopes, as a tracer in biomedical applications, and for trace element analysis of stable isotopes. The use of particle accelerators, along with mass spectrometric methods, has allowed low‐concentration measurements of small‐volume samples. The use of AMS to directly count ions, rather than measure radiation from slow radioactive decay processes in larger samples, has resulted in sensitivities of one part in 1015. The ions are accelerated to mega‐electron‐volt energies and can be detected with 100% efficiency in particle detectors. The improved sensitivities and smaller sample sizes have resulted in a wide variety of applications in anthropology, archaeology, astrophysics, biomedical sciences, climatology, ecology, geology, glaciology, hydrology, materials science, nuclear physics, oceanography, sedimentology, terrestrial studies, and volcanology, among others. Accelerator mass spectrometry has opened new areas of research in the characterization of trace elements in materials.

This article will focus is on the technique of trace element accelerator mass spectrometry (TEAMS) and its applications in the analysis of stable isotopes in materials.

Trace element AMS employs a tandem electrostatic accelerator with the center terminal at a positive potential.

Sensitivities for TEAMS measurements vary for different elements. These sensitivities depend on (1) the ability to form a negative atomic ion or a negatively charged molecule that can be accelerated to the terminal and then broken apart; (2) the charge state used for the measurements since the charge state (≥3+) must be chosen to remove molecular interferences; and (3) transmission of the ion from the sample through the accelerator and beamlines to the detector. By calibrating the secondary‐ion yield against reference standards and by measuring the depth of the sputtered crater, a quantified depth profile can be obtained. The sensitivity or detection limit depends on the amount or volume of material available to analyze. The sensitivity can be much better for bulk measurements, where the element of interest is uniformly dispersed throughout the material. Then, the sample can be run almost indefinitely until good statistics have been obtained. Typically, sensitivities of 0.1 part per billion (ppb) can be obtained in the depth‐profiling mode. Because sensitivities are so high, it is sometimes difficult to obtain suitable reference standards.
Introduction To Medium‐Energy Ion Beam Analysis
Authors: Weller Robert A.
Published: October 2003

The earliest applications of ion beam techniques for materials analysis, typified by the work of Tollestrup et al. (1994), were carried out with mega‐electron‐volt beams in the course of basic research in nuclear physics, and the mega‐electron‐volt beam techniques still form the indispensable core of the subject. In the broadest sense, the importance of these techniques lies in the fact that the information they yield depends upon nuclear properties and interactions and is, therefore, relatively insensitive to perturbation by local properties such as the chemical environment and electronic structure. The relevant nuclear physics and scattering theory are well known experimentally and often theoretically, and in consequence, important parameters such as interaction cross‐sections are known from first principles. This is in sharp contrast to the situation for some other important techniques (e.g., secondary ion mass spectrometry) where the fundamental measurement interactions may be very vulnerable to the unique idiosyncrasies of a specimen. It is essential to stress the unity of ion beam analysis even as one seeks to differentiate the relatively newer medium‐energy techniques from their more mature high‐energy predecessors.

First it is important to understand what is meant by “medium energy.” There are two answers, one historical and one based upon the physics of scattering. For practical purposes, medium energy encompasses ion beam energies from a few tens of to a few hundreds of kilo‐electron‐volts, and even a bit higher for heavy ions being used in forward‐recoil work. Below this range, ion scattering becomes increasingly surface specific. Above it lies the full range of conventional elastic scattering and nuclear reaction analysis.

Historically, medium energy has been defined by technology. The field of ion beam analysis owes its ubiquity, if not its existence, to a single device, the silicon surface‐barrier particle detector.

The articles in this category follow describe some medium‐energy ion beam analytical techniques that are optimized for different problems. Time‐of‐flight medium‐energy backscattering and forward‐recoil spectrometry, are quite similar to the high‐energy techniques of high‐energy ion beam analysis but offer increased depth resolution, sensitivity, and surface specificity at the expense of total analyzable depth and ease of use.

Heavy‐ion backscattering spectrometry is a variant of time‐of‐flight backscattering that is optimized for the highest possible sensitivity, specifically for the measurement of ultra‐low‐level metallic contaminants on device‐grade Si wafer surfaces. Along with total‐reflection x‐ray fluorescence spectrometry, it is the definitive method currently available for this measurement. Medium‐energy techniques are appropriate for specialized problems and circumstances as described in the articles.
Heavy‐Ion Backscattering Spectrometry
Authors: Banks James C. , Knapp James A.
Published: October 2003

Heavy‐ion backscattering spectrometry (HIBS) is a new technique for nondestructively analyzing ultratrace levels of impurities on the surface of very pure substrates. Although any high‐Zcontaminant (Z≥ 18) on a pure low‐Zsubstrate can be measured, recent practical applications for HIBS have focused on measuring contaminants found on silicon wafers used in semiconductor manufacturing. Therefore, discussions of HIBS focus in this area. The technique is based on the same principles described for high‐energy Rutherford backscattering spectrometry (RBS) and medium‐energy ion backscattering spectrometry.

The motivation for HIBS is to detect metallic contamination at levels significantly below those that can be detected by RBS or medium‐energy ion backscattering, both of which have a limit of ∼1 × 1013atoms/cm2for near‐surface impurities. It had been reported that contamination control in the microelectronics industry will require tools that can measure ∼1 × 1010atoms/cm2for transition metals in starting material. The detection limit for well‐separated elements on a clean Si surface ranges from ∼6 × 109atoms/cm2for Fe to ∼3 × 108atoms/cm2for Au, without the use of vapor phase decomposition (VPD) to preconcentrate the impurities. Using VPD would improve the sensitivity by at least an order of magnitude.

The HIBS technique is illustrated Other surface analysis techniques for detection of trace element contamination are briefly discussed, with the strengths and weaknesses of each compared to those of HIBS. A detailed discussion of the basic theoretical and practical aspects of HIBS is provided.
Alkyd Resins
Authors: Wicks Zeno W.
Published: October 2003

Chemistry, processing, and uses of various types of alkyds are discussed, including oxidizing and nonoxidizing alkyds, high solids, styrenated alkyds, siliconized alkyds, and waterborne alkyd resins. Also covered are the related uralkyd and epoxy ester resins.
Barrier Polymers
Authors: Dhoot Sushil N. , Freeman Benny D. , Stewart Mark E.
Published: October 2003

Although broadly defined as a macromolecule having the ability to restrict the passage of gases, vapors, and liquids, the functional definition of a barrier polymer varies from application to application and a material that provides sufficient barrier for a particular end use can be considered to be a barrier polymer. They are widely used in food, beverage, and other packaging industries. Some of the advantages that they offer over traditional packaging materials such as glass, paper, and metals are flexibility, light weight, toughness, versatility, and printability. However, unlike glass and metals, no polymer offers an infinite gas barrier. Combinations of different polymers, or polymers with inorganic materials, in the form of multilayer structures or blends, can provide sufficient barrier for the intended shelf life of most products. Inorganic materials such as silicon and aluminum oxides and nanoclays can significantly enhance barrier and other mechanical properties of polymers. Other approaches for improving barrier properties such as oxygen‐scavenging systems have also received considerable attention in recent years. This article discusses various types of barrier polymers and structures, their permeability characteristics (including the underlying principles involved), measurement techniques, ways to predict and improve barrier properties, and current as well as potential future applications for barrier polymers.
Block Copolymers
Authors: Hamley I. W.
Published: October 2003

The synthesis, morphology, and dynamics of block copolymers in various states is reviewed. Living polymerization techniques used to prepare well‐defined diblock, triblock, and starblock copolymers are first summarized. Then the phase behavior of block copolymers in the melt is discussed, based on experimental and theoretical work. The effect of confinement on block copolymers in thin films is then considered. The behavior of block copolymers in solution and applications resulting from micelle formation are also reviewed. The effect of crystallization on block copolymer morphology is also outlined. Finally, the competing effects of micro‐ and macrophase separation in blends of polymers containing block copolymers is described, along with compatibilization of immiscible polymers by block copolymers.
Butadiene Polymers
Authors: Kerns Michael , Henning Steven , Rachita Michael
Published: October 2003

This article provides an overview of polybutadiene materials as a progression from the monomer 1,3‐butadiene to a useful polymer product with a wide range of applications. A brief history of polybutadiene, with its development as a highcis‐polybutadiene material during World War I through its present day use as a high vinyl substitute for styrene–butadiene rubber is included. The structure and properties of the monomer are presented, along with monomer manufacture, typical specifications, and health and safety issues. Following a detailed discussion on both polymer microstructure and macrostructure, there is an in‐depth review of polymerization methods that are typically used to produce polybutadiene. The state‐of‐the‐art in free‐radical, Ziegler–Natta, anionic, and cationic polymerization techniques that produce polybutadiene are thoroughly discussed in terms of the influence of catalyst/initiator technology on microstructure and the resulting relationship between microstructure and applications. The most popular commercial polymerization processes are also reviewed including solution, emulsion, and an introduction to gas‐phase polybutadiene polymerization technology. Finally, the economic aspects of polybutadiene materials are presented, including major producers, capacities, and pricing.
Cellulose Esters, Inorganic
Authors: Shelton Michael C.
Published: October 2003

Inorganic esters of cellulose have a valuable place in history, from the birth of the plastics industry to elucidation of the genetic code. It is important not to forget the large number of applications in which these materials have played a role: coatings, explosives, pharmaceuticals, membranes, and synthetic intermediates. Although inorganic esters of cellulose have been around for over 100 years, these materials remain important tools for coatings scientists, explosives experts, and biochemists. This article provides a summary of work on inorganic esters of cellulose, including cellulose nitrate, cellulose phosphate, cellulose sulfate, and cellulose sulfonates.
Cellulose Ethers
Authors: Majewicz Thomas G. , Erazo‐Majewicz Paquita E. , Podlas Thomas J.
Published: October 2003

Cellulose ethers is the common terminology for a group of cellulose derivatives that are soluble in aqueous or organic media. They are additives in many formulations and function primarily to control solution rheology. This article surveys the chemistry, properties, and characterization methods common to cellulose ethers and their manufacture and provides general health and safety factors. In the discussion of commercial cellulose ethers, greater detail for individual cellulose ether compositions, including carboxymethylcellulose, hydroxyethylcellulose and its mixed ethers, methylcellulose and its mixed ethers, ethylcellulose, hydroxyethylethylcellulose, and hydroxypropylcellulose is offered.
Chromatography, Affinity
Authors: Scouten William H.
Published: October 2003

Affinity chromatography a rapid and highly efficient means of protein purification utilizing the highly selective ability of enzymes to recognize certain biological compounds or their analogues. This technique involves the immobilization of an appropriate ligand in such a way that the enzyme is still capable of recognizing and binding to the immobilized form of the ligand, whereas contaminating proteins have no such recognition. Virtually hundreds of proteins have been purified in this way, using a wide variety of bioligands immobilized in a matrix; enzyme inhibitors, coenzymes, antibodies, and even other enzymes may be useful bioligands in the purification of a particular protein. This article discusses ligands, matrices, and applications of this separation and purification technique.
Chromatography,
HPLC
Authors: Brun Yefim
Published: October 2003

A comprehensive review of high performance liquid chromatography (hplc) of biological and synthetic polymers is presented. Instrumentation, individual modes of separation, theoretical background (both thermodynamic and dynamic factors), and applications are discussed. High performance liquid chromatography is widely used for isolation and purification of biopolymers and analysis of additives in complex polymer formulations. The potential of hplc for bioseparations is analyzed in the light of recent development in reversed‐phase, hydrophobic‐interaction, and ion‐exchange chromatographies. Miniaturization of separation and other problems related to coupling column chromatography to mass spectrometer detection, as well as multidimensional separations, are considered in some detail.

High performance liquid chromatography is a powerful tool for characterization of synthetic and natural polymers by separating individual fractions by molecular weight, chemical composition, functional groups, etc. Normal‐ or reversed‐phase gradient separation of synthetic copolymers and polymer blends provides information about polymer's chemical composition distribution, and is considered as a technique complimentary to size‐exclusion chromatography. Two‐dimensional copolymer characterization is achieved by coupling two different modes of chromatographic separation consequently, which can result in determination of both molecular weight and chemical composition distributions of synthetic copolymers.
Coating Methods, Powder Technology
Authors: Richart Douglas S.
Published: October 2003

Methods for applying decorative and protective coatings utilizing finely divided powders followed by heat fusion of the powder particles to form a continuous film are gaining in popularity and commercial acceptance. Since there are no volatile organic compounds present, powder coating is an environmentally friendly, nonpolluting coating process, providing coatings with improved performance as well. Powder coatings can be found on many common items including lawn and garden equipment, outdoor metal furniture, display racks, architectural aluminum panels and trim, and many automotive components including the exterior clear coat.

The chemistry and composition of powders used in coatings and their properties are described, as well as their method of manufacture, processes used to apply them, their applications, and a review of health, safety, and environmental considerations. Over 100 references are supplied to provide more detailed technical information.
Coating Methods, Survey
Authors: Cohen Edward D. , Gutoff Edgar B.
Published: October 2003

Coating process technology is used to produce a wide variety of products, such as surface coatings to protect houses, bridges, and automobiles; packaging materials to store food; adhesives for use in labels; photographic films; optical and magnetic media for audio and visual use data storage; glossy paper for magazines; and printing plates. The coating machine, which produces the coated web, has several steps. The web is unwound and transported through the coater, then a coating applicator applies the coating which is then solidified, and finally the web is rewound. The coating machine can also contain devices to modify the surface properties, to clean the web, to measure coating weight, and to laminate a second web to the structure.

Many of the commercially available coating applicators are described, including units for simultaneous multilayer application, for discrete coating, and for patch coating. While convection drying is emphasized, brief descriptions of conduction and infrared heating, as well as of uv and electron‐beam curing, are given.
Collagen
Authors: Ramshaw John A. M. , Glattauer Veronica , Werkmeister Jerome A.
Published: October 2003

Collagen is the most abundant animal protein, being the principal protein component of all connective tissues, including skin, bone, tendon, and cartilage. There are at least 21 distinct collagen types. All play a structural and/or functional role in the extracellular matrix. All are characterized by the triple‐helical structure, which leads to a repeating Gly‐X‐Y amino acid sequence. Each collagen chain has a precise, genetically determined molecular size, which may be further modified during biosynthesis by a range of secondary modification processes. In functional tissues the major collagens form into ordered, cross‐linked fibrils. Minor collagens display a range of other aggregate structures. Collagens can be prepared from a variety of tissue sources, and are now available as recombinant proteins. Test methods are available for quantitation and for assessing purity, stability, and biological properties. Collagen is a valuable and widely used polymer in manufactured products, including leather and gelatin. A growing market is emerging for collagen in a range of biomedical applications. The long history of successful applications for collagen indicates that it is a safe material.
Cotton
Authors: Wakelyn Phillip J.
Published: October 2003

Cotton is both a fiber and a food crop that is grown in about 80 countries. Annually in the world about 90 million 217.7‐kg (480‐lb) bales [∼19.6 million metric tons (21.6 million tons)] of cotton fiber and 27 million metric tons (29.8 million tons) of cottonseed are produced. Cotton is the most important natural fiber (about 37% of the textile fiber consumed in the world in 2002) used to produce apparel, home furnishings, and industrial products. Cottonseed is the world's no. 3 oilseed, used for vegetable oil, animal feed, and linters. Over 90% of the world's cotton production is upland cotton (Gossypium hirsutum) and about 8% is extra long staple (G. barbadense). In 2002 transgenic varieties are about 25–30% of the cotton grown in the world. Commercial cottons are white. There has been some interest in naturally colored cottons (shades of brown and green are the main colors) and organic cotton but, at present, there is very little production of these cottons [<20,000 bales worldwide; <4455 t (4800 tons)]. The origin, biosynthesis, biology, development, production, harvesting ginning, classification, physical properties, morphology, physical structure, chemistry, reactivity, economic aspects, utilization, and health and safety are reviewed.
Critical Phase Polymerizations
Authors: Jones Charles A. , DeSimone Joseph M.
Published: October 2003

Carbon dioxide is a versatile, environmentally benign solvent for the synthesis of many polymeric materials. This review focuses on recent advances in the utilization of liquid and supercritical CO2as a reaction medium for polymer synthesis. Polymerization techniques with both chain‐growth and step‐growth mechanisms are discussed, including free‐radical, metal‐catalyzed, ionic, and bulk polycondensation processes.
Diacetylene and Triacetylene Polymers
Authors: Fowler Frank
Published: October 2003

The polyacetylenes, polydiacetylenes, and polytriacetylenes are the only known families of linearly conjugated polymers. The polydiacetylenes and polytriacetylenes, the primary topic of this discussion, are distinguished from the polyacetylenes because they require preorganization of the monomer for a successful polymerization. These topochemically controlled polymerizations have the interesting property that they can lead to single crystals of conjugated polymers, a unique structural feature among all polymers. The conjugated backbones impart interesting optical and electrical properties to these polymers, making them possible candidates for the development of advanced materials.
Enzymatic Polymerization
Authors: Kobayashi Shiro , Uyama Hiroshi
Published: October 2003

This article deals with recent advances in enzymatic polymerizations, defined as chemical polymer synthesisin vitro(in test tubes) via nonbiosynthetic pathways catalyzed by an isolated enzyme. The principal target macromolecules via the enzymatic polymerization are polysaccharides, poly(amino acid)s, polyesters, polycarbonates, polyaromatics, and vinyl polymers.

For synthesis of polysaccharides, poly(amino acid)s, polyesters, and polycarbonates, hydrolases are used as catalyst; hydrolases, enzymes catalyzing a bond‐cleavage reaction by water, induce the reverse reaction of hydrolysis, leading to polymer production by a bond‐forming reaction. Specific enzyme catalysis provides a novel synthetic route for not only natural biopolymers such as cellulose, xylan, and chitin, but also unnatural polysaccharides, polyesters, poly(amino acid)s, and polycarbonates, many of which are difficult to be synthesized by conventional methodologies.

Oxidoreductases act as catalyst for oxidative polymerization of phenol, aniline, and their derivatives, for polymer modification via oxidative coupling, and for production of vinyl polymers. A new class of phenolic polymers are synthesized without use of toxic formaldehyde under mild reaction conditions. Enzyme‐model complexes also catalyze the synthesis of new phenolic polymer materials.
Ethylene–Norbornene Copolymers
Authors: McNally Donal
Published: October 2003

A new family of addition copolymers based on ethylene and norbornene became commercially available in 2001. These totally amorphous copolymers are strong, stiff, highly transparent, and colorless and have very high moisture barrier as well as interesting electrical properties. This article describes the raw materials, manufacturing, properties, and applications of these new materials.
Ethylene–Propylene Elastomers
Authors: Noordermeer Jacobus W. M.
Published: October 2003

Ethylene–propylene–diene rubbers, commonly called EPDM or EPM, continue to be one of the most widely used and fastest growing synthetic rubbers. They are particularly known for their excellent ozone and aging resistance in comparison with natural rubber and polydiene synthetic rubbers. The technology of producing EP(D)M rubber is still very much in development. Later years have seen major breakthroughs in production technologies relative to the solution and slurry processes based on Ziegler–Natta catalysis, ie, gas‐phase technology and technology based on metallocene catalysis.

EPDM rubber can be extended with fillers and oil plasticizers to a very high level, leading to an attractive price/performance ratio in comparison with other rubbers. EPM can be vulcanized radically by means of peroxides; a small amount of built‐in nonconjugated diene monomer in EPDM permits conventional vulcanization with rubber. Particular emphasis is put on the different processing steps involved in the production of vulcanized EPDM articles. Typical applications of EP(D)M are in automotive weatherstrip profiles, solid and sponge, and radiator hoses; in building and construction as sealing profiles and roofing foils; in cable and wire as insulating and jacketing material; in blends with general‐purpose rubbers to improve ozone resistance; as impact modifier for thermoplastics; and as additive to lubricating oils.
Fractography
Authors: Ehrenstein G. W. , Raue F.
Published: October 2003

This article gives a brief overview about the science of fractography, which comprises the visualization, description, and interpretation of a fracture or a fracture surface, often in order to establish structure–property relationships.

First, the basic observation methods are outlined. Optical microscopy is a simple and inexpensive method to obtain an overall view. However, the depth of field is insufficient at large magnifications. Therefore, when evaluating the topology of a surface, scanning electron microscopy is widely used.

The fracture modes are classified and illustrated with examples of fracture surfaces of polymeric materials. Here, the modes are divided into load fractures, fatigue fractures, influence of chemicals, and special crack causes. The appearance of the surface gives clues to the origin of the fracture and the load which lead to the failure.

Finally, the quantitative evaluation of fracture surfaces is discussed. Quantitative fractography describes the surface in terms of parameters such as roughness, fiber orientation, phase content, and particle size distribution.
Graft Copolymers
Authors: Hadjichristidis N. , Pispas S. , Pitsikalis M. , Iatrou H. , Lohse D. J.
Published: October 2003

Graft copolymers are composed of a main polymer chain (the backbone) to which one or more side chains (the branches) are chemically connected through covalent bonds. They are widely used today in many applications. This is mainly because of the great versatility in making such polymers and the utility they have. Herein we describe the great variety of methods that have been developed to make them and some of the uses to which they have been put.
Inorganic Polymers
Authors: Bourke Sara C. , Manners Ian
Published: October 2003

This article is an overview of inorganic polymer science. In the area of main group polymers, a synopsis of polyphosphazenes and polysilanes is offered followed by more comprehensive reviews of polygermanes, polystannanes, boron‐containing polymers, polycarbophosphazenes, sulfur–nitrogen–phosphorus polymers, and polyoxothiazenes. Polymers based on transition elements are also covered and the survey includes ferrocene‐based polymers, face‐to‐face metallocenes, coordination polymers, and rigid‐rod organometallic polymers.
Light‐Emitting Diodes
Authors: Greiner Andreas , Weder Christoph
Published: October 2003

During the 1990s, light‐emitting diodes (LEDs) have been developed, in which the semiconducting, electroluminescent (EL) material is a polymer. These devices, usually referred to as polymer LEDs, or PLEDs, have attracted significant attention in academic and industrial environment, as reflected by the already more than 5000 scientific publications and numerous patents that address this subject. This article presents an overview of fundamental concepts, with focus on the application of PLEDs. Device physics and general device design, as well as materials concepts, have been addressed. Furthermore, the development of EL polymer systems is discussed based on important key design considerations. Finally, the perspectives for the technological exploitation of PLEDs are elucidated.
Liquid Crystalline Polymers, Main‐Chain
Authors: Chung Tai‐Shung , Cheng Si‐Xue , Jaffe Michael
Published: October 2003

This review covers the most recent study on the nature of thermotropic liquid crystalline polymers (LCPs) and their progress. We summarize and review the newly developed thin‐film polymerization technique for the investigation of liquid crystalline formation as a function of monomer moieties, and for the study of reaction kinetics, the evolution of liquid crystal texture, and surface energy during polycondensation reactions. We also highlight various modification approaches to yield main‐chain LCPs suitable for conventional processing equipment, without compromising the unique liquid crystalline characteristics and the superior mechanical properties. The thermal stability, degradation behavior, and crystallization kinetics of commercial available main‐chain LCPs are recapitulated. Attention is also given to the rheology, polymer blends, micro‐ and nanostructures, and processing of LCPs and their applications.
Lithographic Resists
Authors: Hinsberg W. D. , Wallraff G. M. , Allen R. D.
Published: October 2003

An introduction to lithographic resists is presented. The principles of lithography are described and the essential attributes resist materials must possess are enumerated. The chemical and physical properties of resists of current technological importance are discussed within this framework, with an emphasis on how functional performance is related to these properties. Finally, examples are provided of how resist materials are being tailored for future lithographic imaging technologies.
Molecular Modeling
Authors: Eichinger B. E. , Khare Rajesh
Published: October 2003

The application of the methods of computational chemistry and physics to polymeric systems within the last two decades has generated an arsenal of techniques that are designed to analyze and predict the properties of this important class of materials. Much effort has been devoted to solving the length and timescale problems that polymers present. Concurrently, accurate force field descriptions of condensed phases, including efforts to treat reacting systems, is enabling significant predictions of properties to be made reliably. Many of these techniques are discussed, as is an array of results that have been obtained by a variety of methods.