Cation transport in isomeric pentanes: effects of temperature, density, and molecular shape

Abstract

The cation mobility (μ+ is measured in n-pentane, iso-pentane, neo-pentane, and mixtures of n- and neo-pentane over conditions from the normal liquid, through the critical fluid, to the low density gas. Most of the liquid data correlate with the reduced temperature T/Tc. The T/Tc reflects free volume and viscosity changes. Comparison is made to neutral molecule diffusion. The transition from viscosity control of mobility in the liquid to density control in the dilute gas occurs over the reduced viscosity region 3 > η/ηc > 0.6, which corresponds to the reduced density region 1.9 > n/nc > 0.5. In the saturated gas nμ+ is similar in all pentanes, but iso- ≥ n- > neo-pentane. At constant density dμ+/dT ≥ 0 for gases. The average momentum transfer cross sections in the n-/neo-pentane mixtures are similar to those in neo-pentane at low T but similar to those in n-pentane at high T. The present findings are combined with previous electron mobility data in addressing the effect of hydrocarbon molecular (external) shape on the electric breakdown strength of gases.