The surface and interfacial properties of a nonionic emulsifier (Tween 80)were studied in polyethylene glycol/air and polyethylene glycol/oil systems. It was found that micelles are formed, and that the CMC, area per surfactant molecule and free energy of adsorption of surfactant to the interface increased as functions of ethylene oxide (E0) content of the solvent molecules. These changes in the surface and interfacial properties of the surfactant are apparently a result of surfactant-solvent interactions, due to hydrogen bonding. A series of oil-in-solvent emulsions was prepared also, and the stabilities and particle size of the emulsions were found to be mainly dependent on the adsorption energy of the surfactant.