Surface Phenomena of Liquid Crystalline Substances Influence of N2 Gas Sorption on Surface Tension

The influence of the sorbed N-2 on the surface tension of the low molecular liquid crystal MBBA (p-methoxybenzylidene-p'-n-butylanilin) has been investigated using the pendant drop method. The time- and temperature-dependent measurements of the surface tension of MBBA have been carried out under different N-2 pressures (I - 15 bar). The time-dependence of the surface tension is interpreted in terms of the sorption process of N-2. The results depend strongly on the liquid crystal (LC) phase, the gas pressure and the gas type. All the temperature-dependence curves of the surface tension of MBBA, obtained at different N-2 pressures, show a similar shape within the experimental temperature range (25-50 degrees C), yet with a systematic decrease of the phase transition temperature isotropic(i)/nematic(n) by the increasing N-2 pressure and thus the increasing concentration of the sorbed gas in the sample. The positive slope of the surface tension-temperature characteristic near the phase transition temperature indicates the development of higher ordered molecular states in the surface layer. The correlation between the i-n phase transition temperature of LCs and the concentration of sorbed gases, the gas type and the impurities in LCs has been also discussed.