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

We have studied the behavior of monopalmitin and monoolein monolayers, spre ad at the air-aqueous phase interface, as a function of temperature and sur face pressure. The subphases were aqueous ethanol solutions at 0.5 and 1 mo l/L. The structural characteristics of these films at interface were deduce d from the pi-A isotherms, as measured with an automated Langmuir-type film balance. The monolayer structure and stability were functions of hydrocarb on chain length and the presence of a double bond. Generally, the factors t hat decreased monolayer stability produced transformations toward configura tions with more expanded structures. Changes in the subphase composition ha d a direct influence on the monolayer molecular structure. This study showe d the existence of interactions between film and ethanol molecules at the i nterface. As a consequence of these interactions, a contraction in the mono layer structure was observed. The magnitude of interactions between monogly ceride and ethanol molecules at the interface depends on the surface pressu re, temperature, and surface composition. Stronger film-substrate interacti ons produced changes in monolayer stability. Relationships between film ela sticity and structural characteristics are also discussed.