SURFACE RELAXATION IN SPREAD INSOLUBLE MONOLAYERS OF CHOLESTEROL AND DIPALMITOYL LECITHIN

Experimental evidence is given for time dependent surface tensions in spread insoluble monolayers of cholesterol and dipalmitoyl lecithin, indicating a relaxation mechanism in the surface. To understand this, it is necessary to account for the Principle of Braun-Le Châtelier. Two different techniques and subsequent analysis are presented: periodic compression and surface expansions, and stepwise surface disturbances. Most of the experimental results indicate a double consecutive reaction in the monolayer; the longest relaxation time for cholesterol is of the order of 102 s and for dipalmitoyl lecithin 103 s. Mixed monolayers of cholesterol and dipalmitoyl lecithin are also considered. © 1992.