CHANGES IN CHOLESTEROL SURFACE FREE-ENERGY COMPONENTS DUE TO ITS PHASE-TRANSITION

Changes in cholesterol surface free energy components as a function of temperature were studied. The components were calculated from the measured contact angles of diiodomethane, tetrabromomethane, water, and glycerol in the range 20-50°C. First, changes in the liquid surface tension components were determined from the measured surface and interfacial tensions. It was found that at the temperatures of cholesterol phase transition (35-40°C) an abrupt change in its surface free energy takes place. The nonpolar, Lifshitz-van der Waals interaction increases by 4.34 mJ/m2, whereas the polar acid-base interaction drops down by 1.0 mJ/m2. However, in effect, between 35 and 40°C the hydrophobicity of the surface increases, because the work of water adhesion decreases from 72.8 to 70.6 mJ/m2, respectively. This finding may be important for a better understanding of the cholesterol deposition inside the blood vessels. © 1993 Academic Press, Inc.