SURFACE PHENOMENA OF LIQUID-CRYSTALLINE SUBSTANCES - TIME-DEPENDENCE OF SURFACE-TENSION

The presently available experimental results on the measurement of the surface tension of liquid crystals have been shortly reviewed. They a re inconsistent either in view of the temperature-dependence behavior of the surface tension near the phase transition temperatures or with respect to the absolute values of the surface tension. As one of our p apers to report the results obtained in our laboratory on the investig ation of the interfacial phenomena of liquid crystalline substances, w e reported in this first paper the remarkable time-dependence of the s urface tension of a freshly formed surface, observed on several liquid crystalline substances, both of low molecular and polymeric, both in the mesophase and in the isotropic phase. After discussed several poss ible processes, which may lead to a time-dependence of the surface ten sion of a freshly formed liquid surface, we suppose that the gas sorpt ion process taking place at the liquid surfaces may be mainly responsi ble for this unusual time-behavior. It has been Further suggested in t he paper that such a remarkable time-dependence may occur on a liquid surface where the molecules are relatively highly ordered or have some particular structures and such ordering or structures will be influen ced sensitively by the presence of certain gas molecules, perhaps eith er as a result of the interaction between the gas molecules and the mo lecules at the liquid surface or as a consequence of the gas-induced r e-organization of the molecules in the liquid surface region. It is in ferred that such time-dependence phenomena may have confused the measu rements of the surface tension of liquid crystalline substances perfor med by the early workers and may have contributed to some of the incon sistencies in the obtained results so far.