Materials Literature
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In homogeneously ordered liquid crystals of the nematic type, two principal dielectric constants can be measured: ϵ1 parallel and ϵ2 perpendicular to the symmetry axis of the liquid crystal. The two dielectric constants may show a very different relaxation behavior. With alkoxy derivatives of azobenzene, only the norm…
The development of stress in evaporated dielectric and metal films, used as optical coatings, has been investigated experimentally by observing the bending of a thin silica strip as it becomes coated. The strip forms one mirror of a laser interferometer mounted within the coating chamber, giving high measurement sensi…
In previous papers1–5 the remarkable properties of a liquid birefringent phase that separates from certain solutions of polypeptides in organic solvents when a limiting concentration is exceeded have been described. This phase, first observed by Elliott and Ambrose1 in solutions of poly-γ-benzyl-L-glutamate (PBLG) sho…
-crystallographic axis in intercrossing branches is circa 80°. The possible origin of this unusual mode of twinning, which involves an 80° change in the orientation of the chain axes in offspring branches from that in parent branches, is briefly presented. The process of evolution of monoclinic polypropylene spherulit…
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Soap films can be subjected to compressive stresses exceeding 1 atm while their thickness is measured optically in an apparatus which is described in detail. It permits forming the film within a ring of porous porcelain whose pores communicate to the outside, whereas the film is in an enclosure in which the air pressu…
In 1889 Reinitzer,1 working with cholesteryl benzoate, discovered a state of matter that was later ter med cholesteric liquid crystals. It is doubtful whether the discovery of liquied crystals would have been made at that time if the optical properties of the cholesteric phase were less pronounced. Like other liquid c…
In Part I of this series the residual linewidths for vanadyl acetylacetonate in toluene were found to be proportional to (T/η), where η is the viscosity, and independent of applied field. Since the solutions are dilute, spin exchange is not important. The residual linewidth is attributed to a spin—rotational relaxatio…
Abstract Theoretical models for the ac and γ e relaxation effects found in chain‐folded polymer crystals (single crystal mats and bulk) are presented and compared with the available dielectric and mechanical loss data for polyethylene and polychlorotrifluoroethylene. Details of morphology and crystal structure that ca…
Thermal expansion is the change in shape and volume of a system due to a temperature change. For liquids, gases, and isotropic solids, thermal expansion is isotropic, involving only a change in volume and requiring, therefore, the measurement of a single parameter to uniquely specify the expansion. Crystalline solids…
Dans V3Si les atomes de vanadium sont disposés suivant des chaînes linéaires denses et on peut appliquer aux électrons d l'approximation des liaisons fortes à une dimension. On constate que l'énergie électronique ainsi calculée s'abaisse par déformation de la maille. Ceci peut constituer une explication, par un effet…
X-ray crystallographic data are of particular importance to the mineralogist. Beyond the considerations of structural chemistry, they provide one of the most accurate methods for phase and/or compositional determination and for obtaining the molar volumes and densities of minerals (Table 5-2). Selected data for approx…
The kinetics of the thermal decomposition of molten sodium nitrate have been studied as a function of temperature in the range 570–760°. The effect of replacing the air over the reactant by argon has been examined. From these measurements, it is concluded that atmospheric oxygen does not participate in the reaction an…
The existence of couple stresses acting on the surfaces of elastic continua together with the usual force stresses had been object of numerous fundamental papers [ 1 , 7–16 ]. For describing the complete deformation a geometrically independent rotation vector had been introduced besides the displacement vector. In thi…
The thermal conductivities of three specimens of well-oriented, annealed pyrolytic graphite have been measured over the temperature range 100–900°K. The conductivity parallel to the deposition plane is analysed in terms of mean free paths using the semi-continuum model of Komatsu and Nagamiya. An expression is derived…
Abstract Niobium pentoxide crystallizes in numerous modifications. The present paper describes their mode of formation, structures, and thermal properties.
Abstract A quantitative estimate is made of the increase Δτ 0 of the critical resolved shear stress for the case of solid solutions containing spherical and coherent precipitates. The interaction between edge dislocations and the coherency strain fields is believed to be the strengthening mechanism. The calculation is…
The effect of pressure to several hundred kilobars has been measured on the lattice parameters of diamond, graphite, and hexagonal boron nitride. The linear compressibility of diamond is independent of pressure. The a axis of graphite (characteristic distance in the plane) is considerably more compressible than diamon…
Abstract By the use of simple models of filled plastics, approximate equations are derived for the elongation to break in the case of perfect adhesion between the phases and for the tensile strength in the case of no adhesion between the polymer and filler phases. By combining these equations with equations for the mo…
The anomalously high permittivity in fine‐grained ceramic barium titanate is explained by the absence of 90° twinning within the grains, giving rise to internal stresses as the ceramic cools below the Curie temperature. Using the Devonshire phenomenological thermodynamic method and a simplified model, the stresses inv…