Pre-transitional surface ordering and disordering at liquid crystal-isotropic liquid interface

The existence of pre-transitional surface ordering and disordering at the liquid crystal-isotropic liquid interface has been established from the surface tension measurements. A spinning-drop technique has been used for this study. Measurements were carried out in the smectic y4(S₄), nematic (TV) and isotropic (I) phases of the liquid crystals and reproducible results were obtained. The results suggest that the equilibrium value of γ changes discontinuously in the N and S_A phases. The slope d_γ/dT is positive for both the isotropic phase just above T_NIas well as for the nematic phase just below it. Similar positive slope has been obtained in the vicinity of T_AN. A positive value of dγ/dt implies excess surface order than that of the bulk interior. From the density measurements it has been observed that there is a correlation between the anomalies in the temperature dependence of surface tension and density in the isotropic phase.