Type Of Concentration Dependence Research Articles

Thermodynamic parameters of solvation of nonelectrolytes in aqueous solutions of amides of carboxylic acids

Interaction and reorganization contributions to solvation enthalpies of nonelectrolytes in aqueous solutions of amides of carboxylic acids with different degree of N-substitution and N-methylpyrrolidone are calculated. The data are discussed using structurally thermodynamic characteristics of water-amide systems obtained by us previously. It is found that the type of concentration dependence of the solvation enthalpy of nonelectrolytes in all solutions investigated is determined by the type of reorganization component. It is shown that the highest solvation exothermicity of nonelectrolytes in water is due to the lowest value of the reorganization contribution in spite of that nonelectrolytes interact weaker with water than with non aqueous components.

Surface and mesoporous diffusion with multilayer adsorption

The theory by the authors on surface diffusion where multilayer adsorption occurs is reviewed and further discussed. The theory is derived from a kinetic-theory approach for homogeneous surfaces, but readily extendible to heterogeneous surfaces. The assumptions made in the BET theory are used. The theory is capable of predicting the increase and the subsequent decrease in surface diffusivity with surface concentration. The required information for the theory is the equilibrium adsorption isotherm. From the theory, one can understand the fact that when the surface concentration approaches zero, the transport surface diffusivity becomes equal to the corrected surface diffusivity or self-diffusivity, which can be estimated readily from existing theories. On the other hand, when the surface concentration approaches infinity, that is, when surface condensation occurs, the surface transport diffusivity approaches zero. A fair agreement is obtained between the data available in the literature and the theoretical predictions. Finally, the concentration dependence of surface and mesoporous diffusivities is classified into five types. The multilayer surface diffusion theory is used to predict all five types of concentration dependence.

Concentration Dependence of the Activation Energy for the Hole Drift Mobility of 9-Ethylcarbazole-3-carbaldehyde Hydrazones

A new type of concentration dependence, i.e., intersite-distance (ρ) dependence, of the activation energy for the hole drift mobility of the 9-ethylcarbazole-3-carbaldehyde diphenylhydrazone (ECH) and 9-ethylcarbazole-3-carbaldehyde methylphenylhydrazone (ECMH) dispersed in polycarbonate (PC) is reported. The activation energy for charge transport in the ECH or ECMH-doped PC systems gradually decreases with decreasing ρ for large values of ρ, becoming nearly constant for small values of ρ. This behavior contrasts with that for the 4-diphenylaminobenzaldehyde diphenylhydrazone (DPH)-doped PC system. Specific intermolecular interactions between ECH or ECMH molecules having a planar carbazole moiety at relatively high concentrations are suggested to be responsible for this concentration dependence of the activation energy.

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 2. Die Abhängigkeit der Abbaugeschwindigkeit von der Polymergesamtkonzentration in guten Lösungsmitteln

AbstractMechanical shear degradation of poly(decyl methacrylate), (viscosity average molecular weight in tetrahydrofuran M̄η = 1,3·106, M̄w/M̄n = 5) in the thermodynamically good solvent tetrahydrofuran has been studied in turbulent flow through a capillary as a function of polymer concentration in the range from 0,22 to 8,9 g/100 cm3. Due to turbulent flow conditions the shear stress, shear rate and shear energy proved to be the same for all concentrations and remained constant during degradation, giving a general insight into mechanism of degradation. The rate of degradation has been followed using molecular weight distribution curves obtained by gel permeation chromatography. The reaction was found to be of first order. Rate constants determined for molecular weights from 3,2–9,5·106 decreased with increasing concentration following a law of the type ki = (K + b·c)−1, K and b being constants for each molecular weight. Hydrodynamic volumes of polymer molecules have been calculated according to models of Rudin as function of molecular weight and concentration. It can be shown that rate constants of degradation and calculated hydrodynamic volumes are proportional for the whole range of molecular weight and concentrations up to 3,6 g/100 cm3. There is also a rather good proportionality between these rate constants and the volumes of polymer coils predicted by de Gennes. This result is an additional confirmation of the concept that hydrodynamic volume governs shear degradation of polymer solutions. Additional experiments show that this type of concentration dependence is also to be found for other polymers in other solvents.

Nuclear quadrupolar relaxation in liquid alloys

Linewidths of the 209Bi nuclear magnetic resonance in liquid bismuth-lead alloys are reported as a function of concentration and temperature. The measured widths contain two components: a part proportional to temperature due to the usual magnetic hyperfine interaction with conduction electrons, and a part which decreases with increasing temperature. The latter is attributed to relaxation produced by an electric quadrupole interaction with diffusing ions. The quadrupolar term measured at 625 K passes through a marked maximum as a function of composition at 50% lead and it is the dominant contribution to the width around this composition at lower temperatures. It is concluded from a review of data for several liquid alloy systems containing nuclei with substantial quadrupole moments that this type of concentration dependence should be regarded as normal and not a peculiarity of the Bi-Pb system.