engleski

Surface conductivity of glass at the solid/liquid interface

The electrokinetic phenomenon of surface conductivity was studied for capillaries of pure fused silica and of a borosilicate glass, in water, dilute aqueous solutions of HCl and NaCl, in methanol and acetonitrile. Measurements were done in the temperature range between 5 and 30°C by a dc linear voltage sweep technique at a rate of 0.2 V/sec or less, and with applied polarization voltages up to ± 40 V. Surface conductivity was calculated from the total specific conductivity measured by two bright platinum electrodes at the mouths of the capillary and from the specific bulk conductivity of the liquid medium measured by a separate pair of Pt electrodes at the same temperature. Absolute values of the surface conductivity were between 10− 9 and 10− 10 ohm− 1. Energies of activation were calculated from the slopes, S, of log vs 1/T curves, observed within a temperature range from 5 to 30°C. The energies E defined as S = E/k were: 45– 55 kJ/mole for the borosilicate glass, and 25– 34 kJ/mole for fused silica in water, in aqueous solutions, and in methanol. In acetonitrile they were 105 kJ/mole for borosilicate glass and 59 kJ/mole for fused silica. The results were interpreted on the basis of the assumption that protonic conductivity is the predominant mode of surface charge transfer, with the rotation of water molecules in the first liquid layer as the rate-determining step.

surface charge transfer ; surface conductivity ; fused silica ; borosilicate glass ; energy of activation

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