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

The temperature dependence curve of surface tension has been measured using computer-aided pendant drop method for several low molecular liq uid crystalline substances (LCs) near their phase transition temperatu res. The results reveal anomalies (positive (partial derivative gamma/ partial derivative T)-values and discontinues change) in the surface t ension vs. temperature curve for all the studied substances, which may indicate the development of highly ordered molecular state in the sur face layer in the defined temperature ranges. Furthermore, a sharp dec rease of surface tension has been observed for two LCs by approaching their crystallization points from higher temperatures, which seems to suggest that something like surface induced freezing occurs at the liq uid surface of those substances by nearing their crystallization tempe ratures. The results are discussed on the basis of statistical thermod ynamic models proposed in the literature.