BEHAVIOR OF PURE AND MIXED DPPC LIPOSOMES SPREAD OR ADSORBED AT THE AIR-WATER-INTERFACE

Liposomes from pure dipalmitoylphosphatidylcholine (DPPC) and mixed DPPC: distearoylphosphatidylcholine (DSPC): soybean lecithin (SL) prepared by the Bangham method with sonication were dispersed into solution or spread at the interface and the kinetics of the surface film formation was studied by measuring and recording the evolution of superficial tension, surface potential, and superficial (C-14 labeled) DPPC density. A simple theoretical approach can describe these kinetics by two processes: irreversible diffusion of closed vesicles into or from the bulk phase, and irreversible transformation of closed spherical vesicles into destroyed ones which form the surface film. Diffusion controls the phenomenon for small initial amounts of liposomes. Transformation controls the phenomenon for important initial amounts of liposomes. The kinetic constant of the transformation, K, does not depend on the technique used to form the surface film (spreading or adsorption). The equilibrium and rheological properties of surface films formed after liposome spreading are compared to those of monolayers.