Effect of ethanol on monoglyceride monolayers at the air-aqueous phase interface

We have studied the behavior of monopalmitin and monoolein monolayers, spread at the air-aqueous phase interface, as a function of temperature and surface pressure. The subphases were aqueous ethanol solutions at 0.5 and 1 mol/L. The structural characteristics of these films at interface were deduced from the pi-A isotherms, as measured with an automated Langmuir-type film balance. The monolayer structure and stability were functions of hydrocarbon chain length and the presence of a double bond. Generally, the factors that decreased monolayer stability produced transformations toward configurations with more expanded structures. Changes in the subphase composition had a direct influence on the monolayer molecular structure. This study showed the existence of interactions between film and ethanol molecules at the interface. As a consequence of these interactions, a contraction in the monolayer structure was observed. The magnitude of interactions between monoglyceride and ethanol molecules at the interface depends on the surface pressure, temperature, and surface composition. Stronger film-substrate interactions produced changes in monolayer stability. Relationships between film elasticity and structural characteristics are also discussed.