The Significance of Volta and Compensation States and the Measurement of Surface Potentials of Monolayers

The thermodynamic analysis of the Volta effect by Koenig was studied for insoluble monolayers at air/water interfaces. Capacity measurements with a frequency bridge and with vibrating plate electrodes were used to test the basicassumptions of Koenig. The compensation effect was studied, and the conditions to verify the compensation method for measuring changes in χ potential were established for different types of spread monolayers. The field effect we reported for zwitterionic molecules is shown now to be an artefact produced by changes in the contact angle at the edge of the working interface at high monolayer pressures, with consequent changes in the geometry of the interfacial condenser. Within experimental limits, Kelvin's assumption that the Volta and compensation potentials are equal and opposite is correct for the systems studied.