Hexatic and crystal phase transitions in thin free-standing liquid-crystal films

Thermal and structural studies have been performed on thin films of n-heptyl-4'-n-pentyloxylbiphenyl-4-carboxylate (75OBC). Similar to 65OBC, a surface hexatic phase is observed for films greater than four molecular layers in thickness. Four- and three-layer films display a single, two-dimensional liquid-hexatic transition. The four-layer heat-capacity anomaly is described well by a divergent power-law expression. The three-layer heat-capacity anomaly is qualitatively the same, although its size is greatly reduced. Also, a surface crystal-E phase is observed immediately below the liquid-hexatic transition(s).