Materials Literature
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The tight-binding approximation and the recursion method are used to study the size dependence of the band gap for small CdS and ZnS crystallites (20--2500 atoms). Because of the lack of accurate experimental data, a simple model of the crystal is considered; one which has no dangling bonds and a symmetrical shape. It…
Measurements of TSD together with surface potential were used to study negative corona discharge effects on the charge stability of Teflon FEP electrets. During charging, liquid formation over the sample surface (clearly visible for long-time corona irradiation) was concluded to be responsible for a decreasing in the…
The linear electro-optic effect in GaP has been investigated in the wavelength range 0.552-1.2 mu m at applied electric field frequencies of 200 Hz and 9.45 GHz. The dispersion of the clamped and unclamped electro-optic coefficients is measured and the fitted constants in the formula describing the clamped electro-opt…
The hydrostatic pressure and temperature dependence of velocities of ultrasonic modes propagated in natural crystals of iron pyrites FeS 2 have been measured. It is confirmed that C 12 is positive; the Poisson ratio shows the usual positive sign; it becomes more positive under pressure and remains positive down to low…
An investigation of several alternative representations of modified effective-range theory (MERT) has been carried out for low-energy electron scattering from the rare gases argon, neon and krypton in an effort to determine the energy range over which they can be applied to the analysis of scattering cross sections. O…
The failure statistics of polyethylene plaques loaded with a know volume fraction of metallic particles of fixed size distribution have been determined. The results are compared with the predictions of the percolation breakdown model. It is shown that the large decrease observed in characteristic strengths at low defe…
The magnetic and structural properties of melt-spun Sm(FeT)12 alloys where T=Ti,V,Al,Cu,Ga,Si and with some containing small amounts of B and C have been studied. The samples are magnetically soft in the as-quenched state. High coercive fields are developed upon heating the samples at temperatures ranging from 750 to…
Polycarbosilane (PCS) is an organic polymer with a skeleton of Si-C bonds. SiC fiber (Nicalon) is produced from PCS in three steps: spinning, curing (rendering the material infusible), and heating. SiC fiber has high tensile strength, high elastic modulus, and excellent thermostability in high-temperature oxidizing at…
Abstract Dynamic mechanical techniques can be used for a rapid estimation of polymer crystallinity with an accuracy of better than ±20%. The advantage of our proposed procedure is that it is absolute and the crystallinity can be instantaneously estimated when the dynamic mechanical analysis (DMA) data is available. A…
Abstract An experimental procedure has been designed for the preparation of aqueous mesophases of (hydroxypropyl)cellulose (HPC) exhibiting a stable low turbidity Sandwich chiroptical filters have been made from these right‐handed cholesteric liquid crystals confined between two parallel glass plates. Their optical pr…
The major categories of homopolymers and copolymers are discussed. These include (1) linear siloxane polymers, [—SiRR'O—] n (with various alkyl and aryl R and R' side groups); (2) sesquisiloxane polymers possibly having a ladder structure; (3) siloxane—silarylene polymers, [—Si(CH 3 ) 2 OSi(CH 3 ) 2 (C 6 H 4 ) m —] n…
Abstract In an attempt to provide information for improving silk fiber and fabric properties including crease recovery and yellowing, silk modification has been studied by using succinic and glutaric anhydrides. Glutarylation has been found to protect silk fibers from yellowing caused by the high energy radiation and…
The electronic structures of mixed-valence heteropoly 12-molybdo-phosphate anions (heteropoly blues) were investigated by electronic absorption spectroscopy and by 17 O and 31 P NMR spectroscopy in aqueous and acetonitrile solutions. The one-, two-, and four-electron reduced forms of α-PMo 12 O 40 3 - (αI, αII, and αI…
Abstract Melting points of poly(vinyl alcohol) (PVA) gels obtained by repeated freezing/thawing cycles of the solutions in mixed solvents of water and dimethyl sulfoxide (DMSO) were measured. PVA solutions in 1–30 and 90 vol % DMSO froze at −40°C. The melting point of a gel increased with an increase in freezing/thawi…
Abstract Miscible blends from plasticized poly(vinyl chloride), and epoxidized natural rubber having 50 mol% epoxidation level were prepared in a Brabender Plasticorder by the melt‐mixing technique. Changes in Brabender torque and temperature, density, dynamic mechanical properties, and differential scanning calorimet…
This chapter surveys the possible ways to influence the molecular and morphological structures of rubber-toughened styrene polymers in industrial production processes. Two important types of production processes are used in industry. The first is polymerization of styrene monomer or its mixture with other monomers in…
Abstract Two kinds of polypropylene with different molecular weight (MI = 15 and 30) were melt‐spun at the spinning temperatures of 210–290°C and take‐up velocities of 0.15–3 km/min. In the cases of the spinning temperatures of 270 and 290°C for MI15 and 250 and 290°C for MI30, the density showed a minimum with increa…
Abstract Different formulations of rubber with chopped coconut fiber (treated and untreated) as reinforcing agent were prepared. These reinforced systems were vulcanized at 153°C and the properties of the vulcanizates were studied by stress–strain, shore A hardness, and abrasion loss measurements. The bonding between…
The use of brittle polymers, such as polyvinyl chloride (PVC) and polystyrene (PS), was limited prior to the development of rubber-toughened polymers in the 1930s and 1940s. PVC has been toughened by the addition of small amounts of acrylonitrile rubber (NBR) and other elastomeric materials. Over 1.5 million tons of r…
The structure, properties, and uses of poly(dimethylsiloxane) are surveyed in relation to its surface activity, with emphasis on the structural basis of this activity: the low intermolecular forces between methyl groups and the unique flexibility of the siloxane backbone. These basic attributes are used to explain the…