Adsorption of 1-Monoglycerides at the Hexane/Water Interface

The interfacial tension of a hexane solution of 1-monomyristin against water was measured as a function of temperature and concentration under atmospheric pressure. The interfacial tension decreases after adding an extremely small amount of 1-monomyristin. The thermodynamic quantity changes associated with the adsorption were evaluated by applying the thermodynamic relations. The adsorbed film of 1-monomyristin exhibits the expanded state on its interfacial pressure vs area curve under this experimental condition. The large negative value of the entropy change at high concentration is related to the restricted orientation of the polar head group of 1-monomyristin at the hexane/water interface. We conclude that the entropy change for the system of 1-monomyristin is smaller than that of tetradecanol because of a greater interaction between the large hydrophilic group of 1-monomyristin and water molecules. An explanation is also given about the difference in energy change for both the systems: the adsorbed film of 1-monomyristin is more stabilized energetically than that of tetradecanol by the greater interaction with water molecules. Copyright 1999 Academic Press.