Mixed Langmuir Monolayers of Gramicidin A and Ethyl Palmitate: Pressure−Area Isotherms and Brewster Angle Microscopy

Isotherms of surface pressure, π, against mean molecular area, A, were obtained for monolayers of gramicidin A (GA), ethyl palmitate (EP), and mixtures of the two spread at the air−water interface of aqueous solutions of CaCl 2 at 15, 20, and 25 °C. Plots of A and of monolayer collapse pressure ( π c ) against mole fraction of GA ( X GA ) both suggest miscibility between GA and EP in monolayers at the working temperatures. The morphology of GA, EP, and GA/EP monolayers on aqueous NaCl and CaCl 2 solutions at these temperatures was studied by Brewster angle microscopy. The two-dimensional GA/EP solution containing numerous small microdomains of condensed phase was visualized at any surface pressure.