SURFACE-POTENTIALS OF WATER, METHANOL AND WATER + METHANOL MIXTURES

The room temperature surface potentials of water, methanol and methanol + water mixtures over the whole composition range have been calculated using a molecular dynamics method to simulate the liquids. The theoretical values obtained for the pure liquids are chi(aq) = +240+/-50 mV and chi(CH3OH) = -250+/-50 mV; in the mixed methanol + water system, the calculated surface potential becomes negative rapidly as methanol is added to water. For methanol, d(chi)/dT has been calculated to be +1.5 mV K-1 at room temperature. Available experimental and theoretical estimates of all these quantities are reviewed critically and compared with our data; it is concluded that theoretical modelling of the type described here can give a good general indication of the sign and magnitude of the surface potentials of simple polar liquids.