8CB-Langmuir Layer at air/water interface: Line Tension vs. Dipolar Repulsion

Langmuir \={ }lms of 8CB, a smectic liquid crystal at room temperature, exhibits coexistence of phases with di{\textregistered}erent thicknesses. With decompression of a 8CB-liquid-monolayer gaseous holes appear in liquid monolayer. Molecular interactions controlling the phase separation include short-range van der Waals attraction and long range dipolar repulsion. At small distances where attraction dominates gaseous domains return to energy-minimizing circular shapes. But with size of the holes increasing beyond a critical value, dipolar repulsion becomes strong enough to deform the domains; forming even labyrinth patterns. We use Brewster angle microscopy to study the \={ }lm. Our objective is to obtain a critical diameter of the domains beyond which they are non-circular. Experimental value will be compared with that from theory.