Viscosity of Several Liquid Hydrocarbons as a Function of Temperature, Pressure, and Free Volume

Abstract

Viscosity measurements have been made on nine pure hydrocarbon liquids at six temperatures ranging from 15.56° to 135°C and at pressures as high as 4000 bars. The samples included rigid bicyclic compounds of relatively high symmetry and three n‐alkanes, n‐C₁₂, n‐C₁₅, and n‐C₁₈. These data were analyzed using the Eyring significant‐structure theory, the Cohen—Turnbull free‐volume model, and the empirical Doolittle equations. All of these equations produced essentially identical fits to the data at atmospheric pressure. The hypothesis that the constants v₀ and v_s in these equations represent the specific volume of a ``solid'' or condensed phase was tested by comparing best‐fit values of these constants with experimental values for the solid‐phase specific volume. The Cohen—Turnbull and Doolittle equations were modified for use at elevated pressures with the result that the values of v₀ necessary to satisfy the equations at high pressures were shown to be analogous to the specific volumes of a glassy state at high pressures. Further, the change in v₀ as a function of pressure was compared with the change in the experimental values of the solid‐phase volume at the melting point as a function of pressure and a definite correlation between the two was established.