DIELECTRIC-CONSTANT EFFECTS ON WATER DISSOCIATION AND ELECTRICAL-CONDUCTIVITY IN WATER PARA-DIOXANE SOLUTIONS

We report 25-degrees-C frequency domain impedance spectroscopy (FDIS) measurements as a function of composition in the water-p-dioxane system. This prototype liquid conductor-insulator system exhibits a 10(7) conductivity change between 0.0 and 0.1 weight fraction water. Fratiello and Douglass and then Clemett observed no corresponding concentration effect in previous self-diffusion measurements on water-p-dioxane. Their findings rule out any explanation of our conductivity data based on molecular mobility or percolation arguments: mobility changes would impact both conductivity and self-diffusion in the same way. Rather, we interpret conductivity results in terms of the solution dielectric constant, epsilon; and epsilon-effects on the H2O-H+-OH- equilibrium. Specifically, we suggest that K(eq) for this equilibrium decreases by approximately 10(16) going from water where epsilon = 78.5 to a 1% water in p-dioxane solution where epsilon = 2.75. As p-dioxane content increases, there are many fewer charge carriers and conductivity decreases. Critchfield, Gibson, and Hall and Clemett, Forest, and Smyth reported experimental dielectric constant-composition data. We used their results together with the Bjerrum-Larsson theory to calculate (1) equilibrium constants and (2) solution conductivities as a function of composition. Calculated results agree with experimental data.