Dynamic surface tensions and dynamic surface potentials

Abstract

Dynamic surface properties are investigated by means of measurements of the surface potential with time. These surface potentials were measured by the principle of the vibrating plate, using a toothed wheel which rotates around an axis parallel to that of the jet. Since surface potential data also give information about the adsorption process, they are compared with the dynamic surface tension data. The methods we used for measuring dynamic surface tensions are the oscillating jet and the inclined plate. For non-ionic surfactants the surface potential is due only to the rearrangements of dipoles at the interface, while for ionic systems a contribution of the electric double layer must also be considered. In this investigation we only consider non-ionics, so that only the dipole orientation is important. We studied the homologous series of n-alcohols, which has already been investigated by means of surface tension, and Triton X-405, which contains 40 ethoxy groups. The main observation resulting from these surface potential experiments is the occurrence of dipole relaxation. This relaxation process interferes with the adsorption process and therefore it is difficult to study the adsorption kinetics by means of surface potential measurements.