Determination of interaction parameter χ1, for poly(vinyl alcohol) and water in gels crosslinked from solutions

The Flory interaction parameter χ₁ of poly(vinyl alcohol)-water systems has been estimated as a function of temperature and volume fraction of PVA, the polymer having been crosslinked from solutions of the same in water. Values are reported for temperatures between 0°C and 90°C and polymer volume fractions between 0.03 and 0.12.     

Pillared layered structures based upon M(III) ethylene diphosphonates: the synthesis and crystal structures of M(III)(H(2)O)(HO(3)P(CH(2))(2)PO(3)) (M = Fe, Al, Ga)

A three-dimensional iron(III) diphosphonate, Fe(III)(H(2)O)(HO(3)P(CH(2))(2)PO(3)), I, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Pbca (no. 61) where a = 9.739(5) A, b = 9.498(5) A, c = 15.940(8) A, V = 1474.4(1) A(3), Z = 8, and R(1) = 0.0380. The structure consists of inorganic sheets pillared by the 1,2-ethylenediphosphonate groups. The sheets are composed of Fe(H(2)O)O(5) octahedra connected through PO(3)C tetrahedra. The corresponding isostructural aluminum (II) and gallium (III) compounds were also synthesized and indexed: II, a = 9.534(1) A, b = 9.255(2) A, c = 15.724(1) A, V = 1387.5(1) A(3); III, a = 9.670(1) A, b = 9.357(2) A, c = 15.862(4) A, V = 1435.4(1) A(3).     

Poly(vinyl alcohol) hydrogels: Reinforcement of radiation-crosslinked networks by crystallization

Aqueous poly(vinyl alcohol) solutions were crosslinked via electron-beam irradiation to form transparent hydrogels of varying crosslinking densities. Typical crosslinked hydrogels with M _c between 3500 and 8000 were weak, easily shattered, nonextensible materials with very low tensile moduli (up to 70 psi) and tensile strengths at break (less than 10 psi). Reinforcement by induction of partial crystallization was accomplished by a two-stage drying process, consisting of a slow dehydration stage at room temperature and an annealing stage at elevated temperatures, which was mainly responsible for the introduction of the crystallites. The swollen hydrogels after the annealing process had crystallinities widely varying between 30 and 65% and polymer volume fractions between 30 and 60%, depending on the temperature-time history of the specimen. These materials showed greatly improved mechanical properties (modulus, ultimate tensile strength, tear strength), as compared to the uncrystallized hydrogels.     

Finite element approximation of a model for phase separation of a multi-component alloy with a concentration-dependent mobility matrix

We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented.     

A computational study into the reactivity of epichlorohydrin and epibromohydrin under acidic conditions in the gas phase and aqueous solution

Ab initio molecular orbital calculations have been carried out upon epichlorohydrin and epibromohydrin at the Hartree–Fock (HF) and Møller–Plesset (MP2) levels of theory to explore the reactivity of these species with respect to nucleophilic attack by water under acidic conditions in the gas phase and aqueous solution. These results suggest that nucleophilic attack occurs preferentially at the epoxy carbon atoms in both the gas phase and aqueous solution. These results are in contrast to those found for nucleophilic attack under basic conditions, where attack at the halocarbon atom is competitive with that at the epoxy carbon atoms. Copyright © 2007 John Wiley & Sons, Ltd.     

Intrinsic viscosity and axial extension ratio of random-coiling macromolecules in a hydrodynamic shear field

The shear dependence of the intrinsic viscosity and the conformation of high molecular weight polyisobutylene in dilute solutions of decahydronaphthalene under shear were determined simultaneously. Experimental variables investigated were the shear rate (0 to 2 × 10³ sec^?1), the molecular weight (1.0 × 10⁷ to 1.7 × 10⁷) and the polymer concentration (1.8 × 10^?4 to 8.4 × 10^?4 g/cc). Correlations allowing concentration and shear rate normalization for any one sample are described. Conformational extention ratios along the orientation direction of the deformed molecule to 1.42 and intrinsic viscosity ratios (sheared to zero shear) to 0.5 were observed.     

Photodot investigation of plastic-strain pattern in flat sheet with a hole

The strain pattern was measured, using the photodot method, in a thin flat 24ST-3 aluminum sheet with a central hole, unidirectionally loaded into the plastic region of the material. Test results are presented and the accuracy of the photodot method is discussed.     

The temperature dependence of impurity-assisted tunneling

The temperature dependence of impurity-assisted tunneling in Al−Al oxide-Pb tunnel junctions has been studied. Impurity-caused peaks in the second derivative of the I–V characteristics of these junctions have been studied at temperatures from 4·2 to 148K. In agreement with previous predictions it was found that the width W of such a peak was related to the temperature T by W=[(5·4 kT)²+W₀²]^1/2 where W₀ is the width of the peak at T=0. The amplitude of a peak was found to be proportional to W⁻¹, and the intensity of a peak (area under the peak) was independent of T.     

Application of the semivariogram to MRI data: a useful approach for the characterization of natural porous rocks

Geostatistics is used to study the heterogeneities of reservoir cores, as well as to observe the orientation of layers inside the cores. This information obtained from geostatistics could be very useful for coreflood simulation programs. In this paper, it has been shown how semivariograms can be drawn using local porosities obtained from magnetic resonance imaging (MRI). These semivariograms are then used to determine the correlation lengths of the porosity in the cores and to qualitatively estimate the degree of heterogeneity in the core samples.