Observations and implications of glycerol-monomolecular film interactions

Abstract

Surface pressure and surface potential studies have been carried out on the effects of the addition of glycerol to the aqueous substrates of various monomolecular films at the air-water interface over the temperature range −8° to +26°. Films studied included various fatty acids, methyl esters, and an alcohol, as well as a diglyceride, two phospholipids and cholesterol. The results show an expansion effect increasing with increasing glycerol content, with the initial degree of expansion of the film on an aqueous substrate, and with decreasing surface pressure. Surface potentials show a decrease, the magnitude of which increases with increasing glycerol content and decreasing area/molecule. The results are interpreted in terms of enhanced interaction between the hydrocarbon portions of the film molecules and the aqueous glycerol substrate, accompanied by a reduced orientation of the substrate by the polar head-groups. Some implications concerning low temperature stability of monomolecular films and glycerol interactions are pointed out.