bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion‐Beam Techniques
Authors: Doyle Barney L. , Horn Kevin M.
Published: October 2003

Ion Beam Analysis (IBA) involves the use of a well‐defined
Beam
of energetic
Ions
for the purpose of
Analyzing
materials. In general, it is the combined attributes of the incident ions' energy, mass, and mode of interaction with the target that distinguish each of the analytic techniques described in this chapter. The range of possible ion‐atom interactions that can occur in a target, and the results of that interaction that produces the detected signal, give each technique specific advantages under specific circumstances. In the articles in this section, IBA techniques are described which utilize ion species spanning nearly the entire periodic table, ion energies which extend from several electron volts to several million electron volts, and detected signals consisting of nuclei, electrons, γ rays, x rays, optical photons, collected electrical charge, and even logic states in digital circuits.
Elastic Ion Scattering for Composition Analysis
Authors: Barbour J.C.
Published: October 2003

Composition analyses for virtually all of the elements on the periodic table can be performed through a combination of elastic ion‐scattering techniques: Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD), and enhanced‐cross‐section backscattering spectrometry (EBS). This article reviews the basic concepts used in elastic ion scattering for composition analysis and give examples of their use. Elastic ion scattering is also used for structure determination utilizing techniques such as ion channeling. Composition determination using ion‐beam analysis (IBA) falls into two categories: composition‐depth profiling and determination of the total integrated composition of a thin region. Unknown species in a sample may be identified using elastic ion‐scattering techniques, but in general, analyses involving characteristic x rays or γ rays are more accurate for determining the presence of unknown constituents. For elastic ion scattering, if the ion beam and ion energy are chosen to have sufficiently high energy loss in the sample, then a composition profile is determined as a function of depth by collecting one ion‐scattering spectrum. To represent accurately the composition profile as a function of depth in the sample, an accurate knowledge of the sample's volume density is required because IBA techniques are insensitive to density. If the density of the sample is unknown, then the depth in the sample is given in terms of an areal density: depth times volume density. When the incident ion beam is very light or the ion energy very high, then the composition as a function of depth may not be resolved fully, in which case the average composition of the layer of interest is determined by integrating the signal. In this way, the number of atoms per unit area (areal density) is determined from the integrated signal.
Nuclear Reaction Analysis and Proton‐Induced Gamma Ray Emission
Authors: Vizkelethy György
Published: October 2003

Nuclear reaction analysis (NRA) and proton‐ (particle‐) induced gamma ray emission (PIGE) are based on the interaction of energetic (from a few hundred kilo‐electron‐volt to several mega‐electron‐volt) ions with light nuclei. Every nuclear analytical technique that uses nuclear reactions has a unique feature—isotope sensitivity. Therefore, it is insensitive to matrix effects, and there is much less interference than in methods where signals from different elements overlap. In NRA the nuclear reaction produces charged particles, while in PIGE the excited nucleus emits gamma rays. Sometimes the charged particle emission and the gamma ray emission occur simultaneously. Both NRA and PIGE measure the concentration and depth distribution of elements in the surface layer (few micrometers) of the sample. Both techniques are limited by the available nuclear reactions. Generally, they can be used for only light elements, up to calcium. This is the basis for an important property of these methods: the nuclear reaction technique is one of the few analytical techniques that can quantitatively measure hydrogen profiles in solids. Since these techniques are sensitive to the nuclei in the sample, they are unable to provide information about the chemical states and bonds of the elements in the sample. For the same reason they cannot provide information about the microscopic structure of the sample. Combined with channeling, NRA or PIGE can provide information about the location of the measured element in a crystalline lattice.

The sensitivity and depth resolution of these methods depend on the specific nuclear reaction.

Although NRA and PIGE are quantitative, in most cases standards have to be used.

These techniques require a particle accelerator capable of accelerating ions up to several mega‐electron‐volts. This limits their availability to laboratories dedicated to these methods or that have engaged in low‐energy nuclear physics in the past (i.e., they have a particle accelerator that is no longer adequate for modern nuclear physics experiments because of its low energy but is quite suitable for nuclear analytical techniques).

This article concentrates on the specific aspects of these two nuclear analytical techniques.
Particle‐Induced X‐Ray Emission
Authors: Campbell John L.
Published: October 2003

Particle‐induced x‐ray emission (PIXE) is an elemental analysis technique that employs a mega‐electron‐volt energy beam of charged particles from a small electrostatic accelerator to induce characteristic x‐ray emission from the inner shells of atoms in the specimen. The accelerator can be single ended or tandem. Most PIXE work is done with 2‐ to 4‐MeV proton beams containing currents of a few nanoamperes within a beam whose diameter is typically a few millimeters; a small amount of work with deuteron and helium beams has been reported, and use of heavier ion beams has been explored. The emitted x rays are nearly always detected in the energy‐dispersive mode using a Si(Li) spectrometer. Although wavelength‐dispersive x‐ray spectrometry would provide superior energy resolution, its low geometric efficiency is a significant disadvantage for PIXE, in which potential specimen damage by heating limits the beam current and therefore the emitted x‐ray intensity. In the proton microprobe, magnetic or electrostatic quadrupole lenses are employed to focus the beam to micrometer spot size; this makes it possible to perform micro‐PIXE analysis of very small features and, also, by sweeping this microbeam along a preselected line or over an area of the specimen, to determine element distributions in one or two dimensions in a fully quantitative manner. Most proton microprobes realize a beam spot size smaller than a few micrometers at a beam current of at least 0.1 nA. In trace element analysis or imaging by micro‐PIXE, the high efficiency of a Si(Li) detector, placed as close to the specimen as possible, is again mandatory for x‐ray collection. To date, PIXE and micro‐PIXE have most often been used to conduct trace element analysis in specimens whose major element composition is already known or has been measured by other means, such as electron microprobe analysis. However, both variants are capable of providing major element analysis for elements of atomic number down to.
Medium‐Energy Backscattering and Forward‐Recoil Spectrometry
Authors: Weller Robert A.
Published: October 2003

Medium‐energy backscattering spectrometry is a variation of Rutherford backscattering spectrometry (RBS) using ions with energies ranging from a few tens to a few hundreds of kilo‐electron‐volts. The ion beam, frequently He
+
, is directed onto a specimen and the number of backscattered ions per incident ion is measured as a function of scattered‐ion energy at one or more angles relative to the beam direction. The fundamental physical process being used is that of a binary collision between the nuclei of an ion in the beam and a near‐stationary atom in the target. In such a collision, the energy of the backscattered ion is determined uniquely by its original energy, the scattering angle (which is the angle between the ion's trajectories before and after the collision), and the ratio of the masses. Consequently, a measurement of the energy of a backscattered ion at a specific angle may be used to infer the mass of the target atom with which it collided. The number of backscattered ions is proportional to the collision cross‐section and the total number of available scattering centers. Since collision cross‐sections are known
a priori
in this energy range, the number of backscattered ions with a given energy is a direct measure of the number of atoms of the corresponding mass in the target.

The method achieves additional richness as the result of a second physical phenomenon, the gradual loss of kinetic energy through collisions as an ion penetrates through matter. This is measured by stopping power (also called linear energy transfer), which is the average energy lost, typically in electron volts per unit of length (measured in atoms per square centimeter) of trajectory in the target. A second factor controlling the energy of backscattered ions is the depth within the target at which the collision occurs. As a result, it is usually possible to extract quantitative information about the distribution of specific species within the near‐surface region of the specimen. For the purposes of this article, it is sufficient to note that for medium‐energy ions the stopping power is dominated by collisions between the nucleus of the projectile and the electrons of the target, so‐called electronic stopping, which results in relatively uniform loss of energy with minimal angular divergence of the beam. Widely accepted semiempirical procedures are available for computing electronic stopping power.

Particle detection technology is an extremely important issue in medium‐energy ion beam analysis. This article also is focus on time‐of‐flight spectrometry optimized for high‐resolution measurements. Other methods, including magnetic and electrostatic spectrometers, pulsed‐beam accelerator systems, and time‐of‐flight spectrometry optimized for other measurements, are discussed briefly along with several other methods for depth profiling, trace‐element identification, and hydrogen measurement. Throughout, special attention is paid to the relationship between medium‐energy backscattering and conventional high‐energy RBS.
Neutron Techniques
Authors: Goldman Alan I.
Published: October 2003

This section explores the wide range of applications of elastic and inelastic neutron scattering to the study of materials. Neutron scattering provides information complementary to several other techniques found in the Encyclopedia. Perhaps most closely related are the x‐ray scattering methods. The utility of both x‐ray and neutron scattering methods in investigations of atomic scale structure arises from the close match of the wavelength of these probes to typical interatomic distances (a few Ångstroms). The differences between these two techniques are discussed.
Neutron Powder Diffraction
Authors: Vogt Thomas
Published: October 2003

The first powder diffraction studies on simple materials such as iron metal using x rays were done independently by Debye and Scherrer (1916) in Germany and by Hull (1917) in the United States. For a long time x‐ray powder diffraction was primarily used for qualitative purposes such as phase identification and the assessment of crystallinity. The use of neutrons for such powder diffraction work has advanced significantly over the past 50 years.

The continuing efforts made in unraveling the structural details of superconducting oxides and the recently discovered oxides exhibiting colossal magnetoresistance have demonstrated the indisputable usefulness of high‐resolution neutron powder diffraction. Modern powder diffraction using neutrons, x rays, and synchrotron x‐ray radiation has developed from a qualitative method some 20 years ago to a quantitative method now used to detect new phases and determine their atomic, magnetic, and mesoscopic structure as well as their volume fractions if they are present in a mixture.

Neutron powder diffraction is a complementary technique to x‐ray powder diffraction and electron diffraction. The greater penetration depth of neutrons, the fact that the neutron‐nucleus interaction is a point scattering process implying no variation of the nuclear scattering length with scattering angle, the independence of the scattering cross‐section from the number of electrons (Z) of an element, and therefore the stronger interaction of neutrons with “light” elements such as oxygen and hydrogen, and its isotope specificity as well as its interaction with unpaired electrons (“magnetic scattering”) make neutrons a unique and indispensable probe for structural condensed matter physics and chemistry. However, x‐ray powder diffraction and, in particular, synchrotron x‐ray powder diffraction can investigate samples many thousand times smaller and have an intrinsic resolution at least one order of magnitude better than the best neutron powder diffractometer. A major drawback for neutron scattering is that it can presently only be done at large facilities (research reactors and spallation sources), whereas laboratory‐based x‐ray scattering equipment provides the same flux much more conveniently. Current governmental policies will not permit the construction or upgrade of present‐day research reactor sources in the United States. The future of U.S. neutron scattering therefore relies solely on accelerator‐based spallation sources. Electron diffraction is a very powerful tool to obtain both real and reciprocal space images of minute amounts of powders. In combination with other supplementary techniques such as solid‐state nuclear magnetic resonance (NMR), which allows, e.g., the determination of Wyckoff multiplicities and interatomic distances by exploiting the nuclear Overhauser effect (NOE), physicists, chemists, and materials scientists have a powerful arsenal to elucidate condensed matter structures.
Phonon Studies
Authors: Stassis C.
Published: October 2003

Until the beginning of this century, the models used to understand the properties of solids were based on the assumption that atomic nuclei are fixed at their equilibrium positions. These models have been very successful in explaining many of the low‐temperature properties of solids, and especially those of metals, whose properties are determined to a large extent by the behavior of the conduction electrons. Many well‐known properties of solids (such as sound propagation, specific heat, thermal expansion, conductivity, melting, and superconductivity), however, cannot be explained without considering the vibrational motion of the nuclei around their equilibrium positions. The study of lattice dynamics—or of phonons, which are the quanta of the vibrational field in a solid—was initiated by the seminal papers of Einstein, Debye, and Born and von Kármán. Initially, most of the theoretical and experimental studies were devoted to the study of phonons in crystalline solids, as the name lattice dynamics implies. At present, the field encompasses the study of the dynamical properties of solids with defects, surfaces, and amorphous solids. It is impossible in a single article to present even a brief overview of this field. The discussion in this article is therefore limited to a brief outline of the neutron scattering techniques used for the study of phonons in crystalline solids.

Indirect information about the lattice dynamical properties of solids can be obtained from a variety of macroscopic measurements. For instance, in some cases, the phonon contribution to the specific heat or resistivity can be easily separated from other contributions and can provide important information about the lattice dynamical properties of a solid. In addition, measurements of sound velocities are particularly useful, since they provide the slopes of the acoustic phonon branches. Since such macroscopic measurements are relatively easy and inexpensive to make in a modern materials science laboratory, they should, in principle, be performed before one undertakes a detailed phonon study by spectroscopic techniques. Direct measurement of the frequencies of long‐wavelength optical phonons can be obtained by Raman scattering and infrared spectroscopy. These experiments provide essential information for solids containing several atoms per unit cell and should be performed, if possible, before one undertakes a time‐consuming and expensive detailed neutron scattering study. Also, for simple solids, information about the phonon dispersion curves can be obtained from x‐ray diffuse scattering experiments.

Presently, the most powerful technique for the study of phonons is the inelastic scattering of thermal neutrons. The technique directly determines the dispersion relation, that is, the relationship between the frequency and propagation vector of the phonons.
Magnetic Neutron Scattering
Authors: Lynn J.W.
Published: October 2003

The neutron is a spin‐particle that carries a magnetic dipole moment of −1.913 nuclear magnetons. Magnetic neutron scattering then originates from the interaction of the neutron's spin with the unpaired electrons in the sample, either through the dipole moment associated with an electron's spin or via the orbital motion of the electron. The strength of this magnetic dipole‐dipole interaction is comparable to the neutron‐nuclear interaction, and thus there are magnetic cross‐sections that are analogous to the nuclear ones, which reveal the structure and dynamics of materials over wide ranges of length scale and energy. Magnetic neutron scattering plays a central role in determining and understanding the microscopic properties of a vast variety of magnetic systems—from the fundamental nature, symmetry, and dynamics of magnetically ordered materials—to the elucidation of the magnetic characteristics essential in technological applications.

One traditional role of magnetic neutron scattering has been the measurement of magnetic Bragg intensities in the magnetically ordered regime. Such measurements can be used to determine the spatial arrangement and directions of the atomic magnetic moments, the atomic magnetization density of the individual atoms in the material, and the value of the ordered moments as a function of thermodynamic parameters such as temperature, pressure, and applied magnetic field. These types of measurements can be carried out on single crystals, powders, thin films, and artificially grown multilayers, and often the information collected can be obtained by no other experimental technique. For magnetic phenomena that occur over length scales that are large compared to atomic distances, the technique of magnetic small angle neutron scattering (SANS) can be applied, in analogy to structural SANS. This is an ideal technique to explore domain structures, long wavelength oscillatory magnetic states, vortex structures in superconductors, and other spatial variations of the magnetization density on length scales from 1 to 1000 nm. This particular technique has enjoyed dramatic growth during the last decade due to the rapid advancement of atomic deposition capabilities.

Neutrons can also scatter inelastically, to reveal the magnetic fluctuation spectrum of a material over wide ranges of energy and over the entire Brillouin zone. Neutron scattering plays a truly unique role in that it is the only technique that can directly determine the complete magnetic excitation spectrum, whether it is in the form of the dispersion relations for spin wave excitations, wave vector and energy dependence of critical fluctuations, crystal field excitations, magnetic excitons, or moment fluctuations. In this overview we will discuss some of these possibilities are discussed.
Electrical Measurements on Superconductors by Transport
Authors: Schwartz Justin , Weijers Hubertus W.
Published: October 2003

This article focuses on techniques for measuring the electrical behavior of technologically important superconducting wires, tapes, and other conductors. Depending on the conditions of measurement, electrical behavior can be interpreted to obtain many technologically important quantities. The interpretation for some of the most common of these quantities are discussed.

When characterizing the electrical behavior of superconductors, it is primarily the voltage‐current relationships that are measured. All other quantities are derived from these. Background conditions for the measurements, including temperature, magnetic field, and stress‐strain state, vary with the specific measurement and type of information being sought.

The most common parameter to be obtained from a transport current‐voltage measurement is the transport critical current (

), which is the maximum current that can be carried by the superconductor in the superconducting state. Often this is determined as a function of temperature and magnetic field. Critical current and the corresponding critical current density (

) are the most important parameters in determining the utility of a superconducting material for applications. The value of

equals

normalized by the cross‐sectional area perpendicular to the direction of the current flow. This area can be defined by a variety of methods that are discussed.

Electrical measurements of transport current are used to determine the critical temperature (

) of the superconductor. This is the temperature below which the material enters the superconducting state and above which it is in the normal state. By measuring

as a function of magnetic field using such an electrical measurement, one can also learn about the magnetic behavior of a high‐temperature superconductor.

Electrical measurements are used to determine the properties of superconductors beyond the superconducting state. Measurements of the resistivity versus temperature (i.e., the current‐voltage relationship as a function of temperature in the normal state) are important for the design of superconducting current leads and magnets. For cables and coils, electrical measurements provide insight into the stability and quench propagation (sudden reversion to the normal state from the superconducting state) behavior. This information is key for the design of a superconducting magnet.

Electrical measurements can be used to estimate the AC losses (i.e., energy dissipation resulting from an alternating current) in a superconducting wire or cable. In this case, the hysteretic behavior is used to estimate the energy dissipation.

This article concentrates on techniques for measuring the current‐voltage (

) relationship in superconducting wires, tapes, and cables. Important differences between LTSs and HTSs are discussed. Emphasis is placed on the

measurement and on the interpretation of the results in the context of the technical information sought from the particular experiment.
Single‐Crystal X‐Ray Structure Determination
Authors: Jacobson Robert A.
Published: October 2003

X‐ray techniques provide one of the most powerful, if not the most powerful, methods for deducing the crystal and molecular structure of a crystalline solid. In general, it is a technique that provides a large number of observations for every parameter to be determined and results obtained thereby can usually be considered very reliable. Significant advances have taken place, especially over the last twenty years, to make the collection of data and the subsequent steps to carry out the rest of the structure determination amenable to the relative novice in the field. This has led to the adoption of single‐crystal diffraction methods as a standard analytical tool.

It Modern crystallography is strongly dependent on the use of the digital computer. Typically, a small single crystal (a few tenths of a millimeter in dimension) of the material to be investigated is placed on a diffractometer and data are collected under computer‐controlled operation. A moderate‐sized unit cell (10 to 20 Å on edge) can yield 5000 or so diffraction maxima, which might require a few day's data collection time on a scintillation counter diffractometer or only hours of data collection time on the newer charge‐coupled device (CCD) area detectors.

From these data the fractional coordinates describing the positions of the atoms within the cell, some characteristics of their thermal motion, the cell dimensions, the crystal system, the space group symmetry, the number of formula units per cell, and a calculated density can be obtained. This “solving of the structure” may only take a few additional hours or a day or two if no undue complications occur.

This article concentrate on the use of X‐ray diffraction techniques as would be necessary for the normal crystal structure investigation. A discussion of the basic principles of single‐crystal X‐ray diffraction is presented followed by a discussion of the practical applications of these techniques. In the course of this discussion, a few of the more widely used methods of overcoming the lack of measured phases, i.e., the “phase problem” in crystallography, are presented. These methods are usually sufficient to handle most routine crystal structure determinations. Space will not permit discussion of other more specialized techniques that are available and can be used when standard methods fail.
Single‐Crystal Neutron Diffraction
Authors: Koetzle Thomas F.
Published: October 2003

This article outlines the basic principles of single‐crystal neutron diffraction measures the elastic Bragg reflection intensities from crystals of a material, the structure of which is the subject of investigation. A single crystal is placed in a beam of neutrons produced at a nuclear reactor or at a proton accelerator‐based spallation source. Single‐crystal diffraction measurements are commonly made at thermal neutron beam energies, which correspond to neutron wavelengths in the neighborhood of 1 Å. For high‐resolution studies requiring shorter wavelengths (∼0.3 to 0.8 Å), a pulsed spallation source, or a high‐temperature moderator (a “hot source”) at a reactor may be used. When complex structures with large unit‐cells are under investigation, as is the case in structural biology, a cryogenic‐temperature moderator (a “cold source”) may be employed to obtain longer neutron wavelengths (∼4 to 10 Å). A monochromatic beam technique is generally used at reactors, which normally operate as continuous wave (CW) neutron sources. At spallation sources, which normally are pulsed, a time‐of‐flight Laue method with a broad range of neutron wavelengths is generally used, and the neutron wavelength is determined from the time‐of‐flight for neutrons to reach the detector. The type of moderator is again generally optimized for the particular application, in a manner similar to what is the common practice at reactors.

A single‐crystal neutron diffraction analysis will determine the crystal structure of the material, typically including its unit cell and space group, the positions of the atomic nuclei and their mean‐square displacements, and relevant lattice site occupancies. Because the neutron possesses a magnetic moment, the magnetic structure of the material can be determined as well from the magnetic contribution to the Bragg intensities.

Instruments for single‐crystal diffraction (single‐crystal diffractometers or SCDs) are generally available among the facilities at the major neutron‐scattering centers. Beam time on many of these instruments is available through a proposal mechanism. A listing of neutron SCD instruments and their corresponding facility contacts are given single‐crystal neutron diffraction and provides examples to illustrate the range of materials that can be studied.
Acetylenic Polymers, Substituted
Authors: Nomura Ryoji , Masuda Toshio
Published: October 2003

The tremendous development in the chemistry of substituted polyacetylenes, which has been made after the mid‐1980s, is surveyed. Focus is placed on the polymerization reaction of substituted acetylenes with various transition metal catalysts, on the precision synthesis of substituted acetylenes, and on the production of functional substituted acetylenes.
Acoustic Properties
Authors: Jarzynski Jacek , Balizer Edward , Fedderly Jeffry J. , Lee Gilbert
Published: October 2003

This article covers the use of acoustics as a molecular probe of polymer structure and describes various acoustic applications of polymers. Sound speed and sound absorption measurements in polymers are useful both as a probe of the molecular structure of polymers and as a source of engineering design properties. Enough theory and experimental details are given to make the presentation understandable, but the emphasis is on the experimental results for polymers. Most of the presentation is for small‐amplitude waves in solid polymers. References to some specialized topics are given.
Acrylamide Polymers
Authors: Huang Sun‐Yi , Lipp David W. , Farinato Raymond S.
Published: October 2003

This article presents an up‐to‐date, broad overview of acrylamide polymers covering their physics, chemistry, synthesis, and technology. Acrylamide polymers constitute a major segment of the global water‐soluble polymers market. The physics and chemistry of acrylamide polymers and copolymers in both the solid and solution states are discussed. Chemical properties and synthetic methods for acrylamide polymerization, copolymerization, and polymer derivatization are thoroughly covered, as are commercial manufacturing processes. The principal applications of acrylamide polymers are discussed, and there is coverage of modern methods of polymer analysis as applied to these materials. Safety and economic issues are also considered.
Acrylic (and Methacrylic) Acid Polymers
Authors: Swift Graham
Published: October 2003

Acrylic polymers are widely used because of their unique properties. This article selectively focuses on polymers that contain acrylic acid and/or methacrylic acid. Their content ranges from <5 wt% to 100 wt% for use in applications such as adhesives, coatings, water‐soluble specialties, and superabsorbent gels. Acidic monomer selection and use may be based on monomer properties and characteristics, but is frequently based only on cost and availability, and this generally tips the choice to acrylic acid. As described, many polymer applications require optimized compositions and molecular weights that are uniquely available only by one of several different polymerization processes such as solution, emulsion, and graft, so as to accomplish commercial viability.
Acrylonitrile and Acrylonitrile Polymers
Authors: Wu Michael M.
Published: October 2003

Acrylonitrile is a versatile and reactive monomer that can be polymerized under a wide variety of conditions and copolymerized with an extensive range of other vinyl monomers because of its polar nature and reactivity. Because of the difficulty of melt processing the acrylonitrile homopolymer, acrylonitrile is usually copolymerized to achieve a desirable thermal stability, melt flow, and physical properties. Acrylonitrile‐containing polymers are used in the areas of textile fibers, carbon fiber percursors, adhesives, binders, antioxidants, medicines, dyes, electrical insulations, emulsifying agents, graphic arts materials, insecticides, leather, paper, plasticizers, soil‐modifying agents, solvents, surface coatings, textile treatments, viscosity modifiers, azeotropic distillations, artificial organs, lubricants, asphalt additives, water‐soluble polymers, hollow spheres, cross‐linking agents, and catalyst treatments. Styrene is the largest volume acrylonitrile comonomer for thermoplastic applications. Styrene–acrylonitrile (SAN) copolymers are inherently transparent plastics with high heat resistance and excellent gloss and chemical resistance. They are also characterized by good hardness, rigidity, dimensional stability, and load‐bearing strength. In general, the styrene component of SAN resins offers clarity, stiffness, and processibility, while the acrylonitrile provides chemical and heat resistance. Because of their inherent transparency, SAN copolymers are most frequently used in clear application. These optically clear materials can be readily processed by extrusion and injection molding, but they lack real impact resistance. SAN resins show considerable resistance to solvents and are insoluble in carbon tetrachloride, ethyl alcohol, gasoline, and hydrocarbon solvents. Polar solvents dissolve SAN. The properties of SAN are significantly altered by water absorption. Commercially, SAN is manufactured by three processes: emulsion, suspension, and continuous mass polymerization. More than 75% of the SAN resin produced is believed to be used captively for acrylonitrile–butadiene–styrene compounding and in the production of acrylonitrile–styrene–acrylate and acrylonitrile–EPDM–styrene weatherable copolymers. SAN resins appear to pose few health problems, and they have been approved by the FDA for direct food contact. Copolymers of acrylonitrile and methyl acrylate and terpolymers of acrylonitrile, styrene, and methyl methacrylate are used as barrier polymers. Acrylonitrile multipolymers containing indene; methyl methacrylate, and α‐methylstyrene are used as poly(vinyl chloride) modifiers for heat distortion temperature and processibility improvement.
Acrylonitrile–Butadiene–Styrene Polymers
Authors: Kulich D. M. , Gaggar S. K. , Lowry V. , Stepien R.
Published: October 2003

Acrylonitrile–butadiene–styrene (ABS) polymers are composed of elastomer dispersed as a grafted particulate phase in a thermoplastic matrix of styrene and acrylonitrile copolymer (SAN). The presence of SAN grafted onto the elastomeric component, usually polybutadiene or a butadiene copolymer, compatabilizes the rubber with the SAN component. Property advantages provided by this graft terpolymer include excellent toughness, good dimensional stability, good processibility, and good chemical resistance. The system is structurally complex. This allows considerable versatility in the tailoring of properties to meet specific product requirements. Numerous grades of ABS are available, including alloys and specialty grades for high heat, flaming‐retardant, or static dissipative product requirements. Good chemical resistance combined with the relatively low water absorptivity (<1%) results in high resistance to staining agents. The three commercial processes for manufacturing ABS are emulsion, mass, and mass‐suspension. ABS can be processed by compression and injection molding, extrusion, calendering, and blow molding. Post‐processing operations include cold forming, painting, and adhesive bonding. As a “bridge” polymer between commodity plastics and higher performance engineering thermoplastics, ABS has become the largest selling engineering thermoplastic.
Adhesion
Authors: Gent A. N. , Hamed G. R.
Published: October 2003

A review is given of factors affecting the adhesion of plastics and elastomers. Particular attention is paid to the various causes of adhesion (or lack of it) and to the interpretation of mechanical tests of the strength of bonded joints in terms of a characteristic fracture energy. Several model experiments are described that allow general conclusions to be drawn of the roles of chemical interlinking, molecular interdiffusion, and energy dissipation within the bulk of a deformable adherend on the measured strength of adhesion.
Adsorption
Authors: Rao Ashwin , Dhinojwala Ali
Published: October 2003

Polymer adsorption finds widespread applications in the stabilization of colloids, food processing, paints, lubrication, and surface modification. In the past two decades there have been numerous studies aimed at improving our understanding of this important phenomenon. This article reviews the instrumental and theoretical advances made in this area and presents important experimental results concerning adsorbed polymers.
Aging, Physical
Authors: Simon Sindee L.
Published: October 2003

Physical aging is an important phenomenon that occurs in all glass‐forming materials, including polymeric glass‐formers. In this article, the manifestations of physical aging and structural recovery are described, including volume recovery, enthalpy recovery, evolution of viscoelastic properties, and the effects of physical aging on failure. Controversies in the field are discussed, including rejuvenation, the temperature dependence of the relaxation time at equilibrium density, and the relative time scales for relaxation of different properties, as well as modeling of structural recovery.
Amino Resins
Authors: Williams Laurence L.
Published: October 2003

Amino resins are thermosetting polymers made by combining an aldehyde with a compound containing an amino (NH2) group. Urea–formaldehyde accounts for over 80% of amino resins; melamine–formaldehyde accounts for most of the rest. The principal attractions of amino resins and plastics are water solubility before curing, colorlessness, excellent solvent resistance, outstanding hardness and abrasion resistance, and good heat resistance. Amino resins provide a wide variety of useful products. Adhesives, the largest single market, are used to make plywood, chipboard, and sawdust board. Other types are used to make laminated wood beams, parquet flooring, and for furniture assembly. Aminoplasts and other thermosetting plastics are molded by an automatic injection‐molding process similar to that used for thermoplastics. The process is best applied to relatively small moldings. The great advantage of injection molding is that it eliminates manual labor costs, thereby allowing amino resins to better compete with thermoplastics. The future for amino resins and plastics seems secure. New developments will probably be in the areas of highly specialized materials for treating textiles, paper, etc, and for use with other resins in the formulation of surface coatings. Most amino resins are based on the reaction of formaldehyde with urea or melamine. The first step in the formation of resins and plastics from formaldehyde and amino compounds is the addition of formaldehyde to introduce the hydroxymethyl group, known as methylolation or hydroxymethylation. The second step is a condensation reaction that involves the linking together of monomer units with the liberation of water to form a dimer, a polymer chain, or a vast network, usually referred to as methylene bridge formation, polymerization, resinification, or simply cure. Precise control of the course, speed, and extent of the reaction is essential for successful manufacture. Amino resins are usually made by a batch process. Both urea– and melamine–formaldehyde resins are of low toxicity. Melamine–formaldehyde resins may be used in paper which contacts aqueous and fatty foods. However, some mills are looking for alternatives.
Amorphous Polymers
Authors: Ngai K. L. , Floudas G. , Plazek D. J. , Rizos A. K.
Published: October 2003

Static and dynamic properties of amorphous polymers are reviewed, with emphasis on experimental data. Various experimental techniques commonly used to probe these properties are described and their individual merits are made clear. The challenging problems that still remain to be solved for a satisfactory understanding of the dynamic properties of amorphous polymers are discussed.
Anionic Polymerization
Authors: Quirk Roderic P.
Published: October 2003

This article presents the fundamental principles of living anionic polymerization, including polymerizable monomers, kinetics and mechanism, stereochemistry, and copolymerization. The importance of anionic polymerization for preparation of model polymers with well‐defined structures and low degrees of compositional heterogeneity is illustrated with respect to molecular weight, molecular weight distribution, copolymer composition and comonomer distribution, stereochemistry, chain‐end functionality, and molecular architecture. Practical aspects of anionic polymerization are considered such as polymerizable monomers, solvents, and initiators. General kinetics, mechanisms, and stereochemistries of anionic polymerizations of styrenes, dienes, acrylates and methacrylates, vinylpyridines, epoxides, thiiranes, lactones, cyclic carbonates, and siloxanes are discussed. Effects of aggregation of the initiator and of the chain‐end on the kinetics of alkyllithium‐initiated polymerizations of hydrocarbon monomers are detailed. Experimental conditions that can cause chain transfer and chain‐termination reactions are presented. Copolymerization behavior, monomer reactivity ratios, and copolymer microstructure for styrenes and dienes are detailed to understand the syntheses of tapered block copolymers and random copolymers.
Antioxidants
Authors: Dexter Martin , Thomas Richard W. , King Roswell E.
Published: October 2003

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reactions can cause degradation of the properties of the polymer, loss of flavor and development of rancidity in foods, and a change in lubricants. The need for antioxidants depends on the chemical composition of the substrate and the conditions of exposure. High concentrations of antioxidants, ie 0.5–2% based on the weight of the polymer, are used to stabilize polymers, such as natural rubber and polyunsaturated oils. Saturated polymers have greater oxidative stability and require relatively low concentrations of stabilizers, ie 0.01–0.05% based on the weight of the polymer. The mechanism by which an organic material undergoes autoxidation involves a free‐radical chain reaction. Thermally induced homolytic decomposition of peroxides and hydroperoxides to free radicals increases the rate of oxidation. Decomposition to nonradical species removes hydroperoxides as potential sources of oxidation initiators. The selection of an antioxidant or system of antioxidants is dependent upon the polymer and the anticipated end use. Low concentrations of antioxidants (<0.01%) are added to polyethylene and polypropylene after synthesis and prior to isolation so as to retard oxidation of the polymers exposed to air. Polyunsaturated elastomers are sensitive to oxidation. Antioxidants are added to the elastomers prior to vulcanization to protect the rubber during drying and storage. The oxidation of food containing fats and oils results in a loss of sensory appeal and eventually rancidness. FDA regulations covering the use of direct food additives are stringent and few new materials have been regulated. The most commonly used materials are butylated hydroxytoluenen‐propyl gallate, α‐tocopherol, and butylated hydroxyanisole. A number of antioxidants have been accepted by the FDA as indirect additives for polymers used in food applications.
Atomic Force Microscopy
Authors: Schiraldi D. A. , Poler J. C.
Published: October 2003

Inherently a surface characterization technique, atomic force microscopy (afm) has been utilized to describe the structure and composition of organic, inorganic, and hybrid polymer systems, ranging from thermosets to thermoplastics, and thermoplastic blends and alloys. Scales ranging from large phases, through lamellar crystals, to individual polymer chains (and repeat units within these chains) have been characterized using afm. Also characterized using afm methods have been thermomechanical properties of these polymers, and surface properties (tribology, hardness, adhesion) of these surfaces.
Biodegradable Polymers, Medical Applications
Authors: Kumar Neeraj , Ezra Aviva , Ehrenfroind Tirtsa , Krasko Michal Y. , Domb Abraham J.
Published: October 2003

Biodegradable polymers have been used in medicine as surgical aids and orthopedic applications. They have been used as hemostats, absorbable sutures, bone fixation aids, nerve‐guided tubes, and for controlled drug delivery. The potential use of biodegradable polymers is in its initial stage as many more applications are expected to be developed in the years to come. The scientific work on biodegradable polymers have generated new polymeric materials and compositions that allow the development of new medical applications. For example, cardiovascular stents are now made from metals, whereas to keep vessel potency, a few months of lumen support might be sufficient. A biodegradable stent that will provide support for sufficient time estimated as a few month may provide a better solution to the problem of restenosis. In addition, a biodegradable stent may release antirestenosis agents embedded in the polymer body to the surrounding tissue. Biodegradable polymers are needed as scaffolds for tissue engineering, gene carriers in gene therapy, and as depot drug formulations for controlled drug delivery. This article touches upon all of these concepts and applications.
Blow Molding
Authors: Belcher Sam
Published: October 2003

This article is comprehensive, beginning with the history, through the many types of blow molding, including resins, machines and tooling that can be used by the novice to the everyday blow molder. It strives to answer the questions: What is blow molding? What plastic resins can be used? What is its competition? Where is its future?
Bulk and Solution Polymerizations Reactors
Authors: Nauman E. Bruce
Published: October 2003

A great majority of polymers are made by bulk or solution polymerizations. Even when there is a competing process, such as gas‐phase or emulsion polymerization, it is likely that bulk or solution process will coexist in order to produce special product grades. A common feature of most bulk or solution polymerizations is the need to remove unreacted monomer, by‐products, and solvents from a highly viscous polymer melt (ref. to devolatilization). Temperature control is a key design issue for vinyl addition polymers while control of stoichiometry, including the removal of reaction by‐products, is the major design issue for condensation polymerizations. Most high volume polymers are made in continuous processes consisting of one or more reactors in series followed by a devolatilization system. Most designs are flexible so that many product grades, including random copolymers, can be made in the same equipment.
Butyl Rubber
Authors: Webb Robert N. , Shaffer Timothy D. , Tsou Addy H.
Published: October 2003

Butyl rubber and other isobutylene polymers in wide use include various homopolymers and copolymers. Low levels of unsaturation for subsequent cross‐linking are incorporated by copolymerization with isoprene. Halogenation at the unsaturation site provides additional cross‐linking mechanisms and covulcanization with highly unsaturated elastomers. Polymers containing star branches, conjugated‐diene sites, divinylbenzene, and brominated
p
‐methylstyrene have also been synthesized. Isobutylene polymers are polymerized by a cationic mechanism, using a Brønsted acid as an initiator and a Lewis acid as a coinitiator, eg, water and aluminum chloride. Molecular weights range from several hundred for terminally unsaturated polybutenes to over a million for elastomer grades.

The
T
g
of polyisobutylene is about −70°C, and the polymer is amorphous in the unstrained state. The polymers exhibit a broad damping peak and a low plateau modulus. They display an exceptionally low permeability to gases, and are widely used as air retention barriers in tires. Optimum physical properties are obtained by compounding with carbon black and other fillers. Various mechanisms are used to cross‐link the compounds into elastomeric vulcanizates. Sulfur is used to provide polysulfidic cross‐links, while resin and zinc oxide cure systems give carbon–carbon cross‐links. Besides inner tubes and innerliners, butyl rubbers are used in blends to improve cut‐growth resistance and wet‐skid resistance. Blends with thermoplastic resins improve toughness. Polyisobutylenes enjoy extensive use as adhesives and caulks, and are chemically modified for use in lubricants as dispersants.