Interfacial characteristics of diglyceride monolayers at the air/aqueous phase interface

The effect of temperature and subphase composition (water and aqueous solut ions of ethanol and glucose) on structural characteristics of some diglycer ides (distearin, dipalmitin, and diolein) at the air/water interface, were studied. Monolayers of 1,2-distearin were found to be condensed, while 1,3- distearin monolayers were more expanded and unstable. Distearin monolayers (mixture of both isomers at 50% wt/wt) basically showed a liquid-condensed structure until the collapse point. The additivity rule was not fulfilled a nd the collapse pressure changed with 1,2-distearin molar fraction, which i s indicative of the existence of interactions between molecules of both lip ids, the mixture being non-ideal. Addition of glucose stabilized the liquid -condensed structure, while ethanol reduced the interval of existence of th is phase. Dipalmitin showed solid, liquid-condensed or liquid-expanded stru ctures, as a function of temperature and surface pressure, but the solid ph ase is predominant. For diolein films, only the liquid-expanded structure w as observed. (C) 2000 Elsevier Science B.V. All rights reserved.