The application of the currently used equations for the reproduction of the temperature dependence of viscosity η of binary solvent mixtures of propylene carbonate (PC) and dimethoxyethane (DME) favors the choice of the Vogel-Fulcher-Tammann (VFT) equation using the ideal glass transition point as the reference temperature To for the estimation of free and blocked (inaccessible) volumes. Reduced plots show that the free volumes as obtained from the VFT equation mainly determine the viscosities of the liquid mixtures; the blocked volumes Vx(To)≡Vo (x: mole fraction of PC) show ideal behavior. The effect of negative excess volumes V E on viscosity, studied in the preceding paper, is examined in comparison with the effect of a temperature decrease. The equal signs of η E and V E can be explained by referring the viscosities to the reference temperature To.

Temperature and composition dependence of viscosity. II. Temperature dependence of viscosity of propylene carbonate-dimethoxyethane mixtures

IN previous articles1,2 we have shown that the equation describes the atmospheric pressure viscosities of many liquids with remarkable accuracy. Equation (1) was obtained from the Cohen and Turnbull relationship between the diffusion coefficient D and “the average free volume per molecule”, Vf, defined by Vf = v−v0, where v is the average volume per molecule in the liquid and v0 the van der Waals volume of the molecule3.

Viscosity of Liquid Water and Superheated Steam

NMR spin—lattice and spin—spin relaxation times have been measured in the associated liquids 1,3‐butanediol, 2‐methyl‐2,4‐pentanediol, glycerol, and 1,2,6‐hexanetriol at resonant frequencies of 10 and 20 Mc/sec and over the temperature range —40° to +40°C using ``spin echo'' techniques. These data were translated into average correlation times using the Kubo—Tomita model of the NMR relaxation process. By using a log Gaussian type of distribution it was possible in all four liquids to reconcile the average correlation times derived from both relaxation times and at both resonant frequencies. The rigid lattice limiting value of T2 and the variation of the distribution width with temperature were also determined.

Nuclear Magnetic Resonance Relaxation in Associated Liquids.

In this study some hydrate melts have been examined. A simple dependence of the viscosity upon the temperature has been developed in terms of free-volume theory. This relationship describes very well the non-Arrhenius behaviour of those salts. The proton-spin lattice relaxation timeT1, as a function of the temperature, has been also measured. It has been found that the temperatureT* at whichT1 reaches a minimum is related to the glass-transition temperatureT0 by exp[K/(T*−T0)]/T1/2*=σ, or exp[γυ*/υf*]/T1/2*=σ, whereσ is dependent on the considered substance and on the radiofrequency. These equations mean thatT* is strictly related to the glass-transition temperatureT0 or to the free volumeυf* at temperatureT*. The relations between these parameters have been experimentally verified.

U. Bernini

Papers

Temperature-dependence of the viscosity and spin-lattice relaxation of some hydrate melts

Viscosity of Liquid Water and Superheated Steam