Dielectric relaxation of 4:1 v/v methanol–ethanol to 90 kbar

Abstract

The effect of pressure on dielectric relaxation in a 4:1 v/v methanol–ethanol mixture has been measured in the range −44 –+22 °C to a maximum pressure of 90 kbar using a tungsten–carbide anvil apparatus. Graphs of the complex capacitance in the complex plane are not semicircles, but are approximately skewed arcs. The frequencies of maximum loss were fitted to a general quadratic in the deviations of the pressure and the reciprocal temperature from a reference pressure and temperature near the middle of the field, and apparent activation enthalpies and volumes were calculated. The model in which molecules are represented by spheres of radius a immersed in a medium of viscosity η predicts that the quantity fmη/T, where fm is the frequency of maximum loss and T the temperature, is independent of temperature and pressure. Its value changes relatively little with temperature but changes by three orders of magnitude in the range 0–70 kbar at 21 °C. Our theories of the transport properties of fluids at very high pressures are therefore quite inadequate. As much of the interior of the earth is made of such fluids, our small understanding of them limits our understanding of the earth’s interior.