Materials Literature
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Using XPS and x-ray-excited Auger electron spectroscopy (XAES), we have studied the variation in surface composition of CuO and Cu2O with a variety of high-vacuum treatments, including vacuum annealing, oxidation and hydrogen reduction. Prolonged annealing of CuO results in the formation of a thick layer of Cu2O at th…
Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a…
A new bismaleimide (BMI) resin system, designated 4504, with excellent heat resistance and good mechanical properties for advanced composites was developed. The 4504 resin was made up of 4,4′-bismaleimidodiphenyl methane, diallyl bisphenol A, and desirable catalysts. The reactivity of 4504 was investigated by gel char…
Changes of reaction variables upon the reaction of jute fiber with acrylonitrile, like concentration of sodium hydroxide, reaction time, and reaction temperature, were studied in the present work. Benzene and dioxane were used as diluents for acrylonitrile and reactions were conducted in their presence in different am…
The influences of processing variables on the mechanical properties of general grade poly-propylene prepared by oscillating packing injection molding under low pressure were reported. The density as a function of oscillating holding pressure was measured using density gradient columns. The existence of spherulites and…
X-Ray photoelectron spectroscopy (XPS) and theoretical calculations show that under certain conditions inner valence molecular orbitals (IVMOs) can form within a rather broad binding energy range (15 eV to 50 eV) in compounds of many elements of the Periodic Table. This results in the appearance of a fine structure in…
The dynamic mechanical properties of both homopolypropylene (PPVC)/Maleated Poly-propylene (PP-g-MA) and ethylene-propylene block copolymer (PPSC)/Maleated Poly-propylene (PP-g-MA) blends have been studied by using a dynamic mechanical thermal analyzer (PL-DMTA MKII) over a wide temperature range, covering a frequency…
We investigated possible physical and chemical changes in inert polymers by means of mechanical milling. No chemical changes were observed. However, in polystyrene we found two glass temperatures after milling, in contrast to one glass temperature in the original material. Under certain conditions crystalline polyethy…
It has become possible in recent years to synthesize new materials under controlled conditions with constituent structures on a nanometer size scale (below 100 nm). These novel nanophase materials have grain-size dependent mechanical properties that are significantly different than those of their coarser-grained count…
A newly synthetic method has been developed for the preparation of block copoly(urethaneimide) (PUI). The copolymer was yielded from the direct reaction of the prepolyurethane terminated with isocyanate and the prepolyimide terminated with anhydride. The latter is prepared by reacting an excess amount of pyromellic di…
Polyurethanes were synthesized from polyester and butanediol with three different diisocyanates, i.e., 4,4´-diphenylmethane diisocyanate (MDI), m-xylene diisocyanate (XDI), and 2,4-toluene diiscynate (TDI). The effect of chemical structures of diisocyate compounds on the degree of crystallinity and the thermal stabili…
The influence of external factors on the formation of various polymorphic modifications of poly(vinylidene fluoride) (PVDF) and the copolymers and blends based on it is examined. It is shown that the formation of a particular conformational structure of the PVDF chains may be controlled by regulating, for example, the…
First principles linear response calculations are used to investigate the lattice dynamics of what is thought to be the third most abundant phase in the lower mantle, CaSiO_3 perovskite. The commonly assumed cubic structure (Pm3m) is found to be dynamically unstable at all pressures, exhibiting unstable modes along th…
Rational engineering of enzymes involves introducing key amino acids guided by a knowledge of protein structure to effect a desirable change in function. To date, all successful attempts to change specificity have been limited to substituting individual amino acids within a protein fold. However, the infant field of p…
To test whether the structure of a protein is determined in a manner akin to the assembly of a jigsaw puzzle, up to 10 adjacent residues within the core of T4 lysozyme were replaced by methionine. Such variants are active and fold cooperatively with progressively reduced stability. The structure of a seven-methionine…
Infrared and Raman spectra of lithium ammonium tartrate monohydrate were obtained in the frequency region at temperatures of 15 - 300 K. No soft phonon mode was observed, so the ferroelastic and ferroelectric phase transition at is of order - disorder type. The ordering of atoms below produces pronounced decreases in…
The frequency of optically excited plasmon oscillations in a metal cluster is studied as a function of cluster size. The model is based on the fact that a sphere filled with free-electron gas forms a cavity with size-dependent eigenfrequencies of the optically excitable TM plasmons. Excitation of plasmon resonances by…
The early stages of nucleation and growth in a mixture of high polymers were studied by time-resolved neutron scattering. During the first 160 min, a slow clustering was evident, indicating a buildup of concentration fluctuations. The clusters formed at the end of this stage had the characteristics of ``critical nucle…
For the first time quasicrystal surfaces produced by in situ cleavage in ultrahigh vacuum have been investigated by scanning tunneling microscopy. Twofold and fivefold surfaces of icosahedral AlPdMn single quasicrystals have been studied. The surfaces were found to be rough. Their structure is determined by cluster ag…
Low dielectric fluorocarbon/SiO2 composite films are developed that exhibit good thermal stability and low dielectric constant by using hexamethyldisiloxane (HMDSO) and prefluorobenzene (C6F6) as the monomer source gases, and argon and oxygen as the carrier gases in a dual frequency, inductively-coupled high-density p…