The effects of pressure on the density, dielectric constant, and viscosity of several hydrocarbons and other organic liquids

Abstract

The effects of pressures up to 4 kbar on the density, dielectric constant, and viscosity of n-pentane, n-hexane, n-octane, cyclopentane, methylcyclohexane, and 2,2-dimethylbutane (DMB) were measured at 30 °C. The pressure effects on the viscosities of n-hexane and n-octane were also determined at 0 and 60°. The densities of diethyl ether and cyclopentanone and the dielectric constant of carbon tetrachloride at high pressures are also recorded. The densities of the hydrocarbons increased by 20–30% and the dielectric constants increased by 11–16% as the pressure was increased from 1 to 4000 bars at 30°, but the viscosities increased by 695–2352% over the same pressure range. Carbon tetrachloride froze at 1500 bars at 30°, and cyclopentanone froze at 3500 bars at about 20°. In agreement with earlier work on other liquids, the value of the Clausius–Mosotti function (ε − 1)V/(ε + 2) for the present compounds decreased slightly with increasing pressure. The viscosity at a given pressure decreased slightly with increasing temperature, and temperature effect increased with increasing pressure. In general, the smaller the compressibility of the liquid, the greater was the effect of pressure on the viscosity; DMB was an exception because its viscosity increased abnormally rapidly with pressure. Molecular structure and liquid structure have greater influences on the pressure dependence of viscosity than on that of density or dielectric constant.