ON THE CONSISTENCY OF SURFACE FREE-ENERGY COMPONENTS AS CALCULATED FROM CONTACT ANGLES OF DIFFERENT LIQUIDS - AN APPLICATION TO THE CHOLESTEROL SURFACE

Contact angles of diiodomethane, bromoform, water, formamide, and glycerol were measured on cholesterol surfaces both bare and precontacted with bile salts (sodium cholate, sodium deoxycholate, and sodium chenodeoxycholate). Ten different sets of the measured contact angles were used for the calculation of the surface free energy components, Lifshitz-van der Waals, γLWs, electron acceptor, γ+s, and electron donor, γ-s. Additionally, contact angles of the same liquids were measured on the pellets of the bile salts. From the calculated values of the components it results that in the case of a bare surface, almost any of the liquid triplets can be used for determination of the surface free energy components. The lowest confidence level can be put to the values obtained from contact angles of the liquid set, including two weakly monopolar liquids (diiodomethane and bromoform), and also that including two liquids with similar strong electron donor and relatively weak electron acceptor interactions (glycerol and formamide). The situation is much more complicated in the case of precontacted surfaces, especially when micelles of bile salts were formed in the solutions in which the cholesterol surface was dipped. The results were very scattered and dependent on the triplet used for the calculations. However, an explanation can be found for such scattered values, based on calculations of the surface free energy of bile salt surface, and on the assumption of the presence of hydrating water molecules around bile salt ones. © 1993 Academic Press, Inc.