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51.
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53.
The d. c. component of birefringence of aqueous carboxymethylcellulose (CMC) under an a. c. electric field was measured at frequencies ranging from 0.1 Hz to 100 kHz. Three samples of different molecular weights were studied with varying degree of neutralization, polymer concentration and added salt concentration. The dispersion curve of birefringence consists of three relaxation bands,A, B andC in order of decreasing frequency. RelaxationB with a negative relaxation strength is ascribed to end-over-end rotation of almost rodlike CMC molecules. RelaxationA with a positive strength is attributed to the relaxation of electrical polarizability along the minor axis of molecule. RelaxationC possesses also a positive strength and is induced by clusters of CMC molecules.Dedicated to Prof. Dr. F. H. Müller. 相似文献
54.
P. Lazzeretti A. Courtot M. Defranceschi G. Berthier 《Journal of Molecular Structure》1997,390(1-3):57-60
The interaction Hamiltonian within the Bloch gauge for the potentials of the electric field has been used to define electric multipole moment operators. Perturbation theory has been applied to evaluate the induced electronic moments and electric field at the nuclei in the presence of spatially non-uniform electric fields of high intensity. Multipole nuclear electric shielding tensors have been defined to describe the contributions arising from a non-homogeneous electric field. These quantities are useful to rationalize linear and non-linear responses of a molecule in the presence of intense external electric perturbations. 相似文献
55.
Ultra-high-molecular-weight polyethylene (UHMWPE) – carbon black (CB) blends were prepared by gelation/ crystallization from
PE dilute solutions containing CB particles. The UHMWPE/CB composition chosen were 1/0.15, 1/0.25, 1/0.5, 1/0.75, 1/1, 1/3,
1/5, and 1/9, etc. The cross-linking of PE chains was performed by chemical reaction of dicumyl-peroxide at 160 °C. X-ray diffraction patterns indicate that the crystallinity of PE within the blends decreased drastically through the chemical
reaction at high temperature. The sample preparation method by gelation/crystallization provided the UHMWPE–CB system with
various CB contents up to 90% and the conductivities for the resultant specimens were in the range from 10-9 to 1 Ω-1 cm-1 corresponding to the electric conductivity range of semiconductors. The blends assured thermal stability of electric conductivity
by cross-linking of PE chains, although the mechanical property such as the storage and loss moduli were very sensitive to
temperature. The conductivity of the blends with CB content ≥20% were almost independent of temperature up to 220 °C and the values in the heating and cooling processes were almost the same. On the other hand, for the UHMWPE–CB blends with
13% CB content corresponding to the critical one, temperature dependence of electric resistivity showed positive temperature
coefficient (PTC) effect. The PTC intensities for non-cross-linked and cross-linked materials were lower than that of the
corresponding low-molecular-weight-polyethylene (LMWPE)–CB blend but the maximum peak appeared at 160 °C which is higher than the peak temperature of LMWPE–CB blend.
Received: 10 December 1997 Accepted: 9 April 1998 相似文献
56.
The electric conduction in the fibrous medium constructed by a homogeneous array of parallel, identical, charged, circular cylinders having an arbitrary zeta potential filled with the solution of a symmetrically charged electrolyte is analytically examined. The thickness of the electric double layers surrounding the dielectric cylinders is assumed to be small relative to the radius of each cylinder and to the gap width between two neighboring cylinders, but the polarization of the mobile ions in the diffuse layers is allowed. The effect of interactions among individual cylinders is taken into explicit account by employing a unit cell model. The appropriate equations of conservation of electrochemical potential energies of ionic species are solved for each cell, in which a cylinder is envisaged to be surrounded by a coaxial cylindrical shell of the fluid solution. Analytical expressions for the effective electric conductivity are obtained in closed forms as functions of the porosity of the fiber matrix and other characteristics of the porous system. Comparisons of the results of the cell model with different conditions at the outer boundary of the cell are made. Under an otherwise identical condition, the electric conductivity in a porous medium composed of an array of parallel cylinders in the transverse direction is smaller than that of a suspension of spheres. The effect of interactions among the cylinders or spheres on the effective conductivity can be quite significant under appropriate conditions. 相似文献
57.
Behaviour of electrolytes confined in cylindrical and slit pores are studied by computer simulations at the molecular level. Previous equilibrium and structural properties obtained by Monte Carlo techniques using the restrictive primitive model are discussed. Transport properties are calculated by the canonical molecular dynamics technique for ions with Lennard–Jones cores. Assuming an external electric potential, the chemical potential of individual ions can be balanced without the need for a grand canonical procedure. The mobility of the counterion is affected by the surface charge density. At a high surface charge, the mean square axial displacement of the counterion calculated is lower than the bulk value due to its high concentration near the charged wall. 相似文献
58.
The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (σst) for amphoteric solid with structural charges was established in order to investigate the effect of σst on pK. The theoretical analysis based on 1-pK model indicates that the independent PZNC of electrolyte concentration (c) exists for amphoteric solid with structural charges. A common intersection point (CIP) should appear on the acid-base titration curves at different c, and the pH at the CIP is pHPZNC. The pK can be expressed as pK=-pHPZNC log[(1 2αPZNC)/(1-2αPZNC)], where αPZNC≡σst/eNANs, in which e is the elementary charge, NA the Avogadro‘s constant and Ns the total density of surface sites. For solids without structural charges, pK=-pHPZNC. The pK values of hydrotalcite-like compounds (HTlc) with general formula of [Mg1-xFex(OH)2](Cl,OH)x were evaluated. With increasing x, the pK increases, which can be explained based on the affinity of metal cations for H^- or OH^- and the electrostatic interaction between charging surface and H^- or OH^-. 相似文献
59.
By the use of complete orthonormal sets of -exponential-type orbitals, where ( = 1, 0, –1, –2,...) the multicenter electronic attraction (EA), electric field (EF) and electric field gradient (EFG) integrals of nonscreened and Yukawa-like screened Coulomb potentials are expressed through the two-center overlap integrals with the same screening constants and the auxiliary functions
introduced in our previous paper (I.I. Guseinov, J. Phys. B, 3 (1970) 1399). The recurrence relations for auxiliary functions are useful for the calculation of multicenter EA, EF and EFG integrals for arbitrary integer and noninteger values of principal quantum numbers, screening constants, and location of slater-type orbitals. The convergence of the series is tested by calculating concrete cases. 相似文献
60.
The effects of high-voltage pulsed discharge (HVPD) activation on the Raman spectra of saturated aqueous solutions of lithium sulfate (Li2SO4/H2O) in the range of the ν1(A) totally symmetric vibrations of the SO 4 2? anion and on the spectra of potassium thiocyanate KSCN/H2O in the region of the ν1(C≡N) vibrations of the SCN? anion have been studied. The temperature dependences of the width and frequency of the corresponding spectral lines have been investigated. 相似文献