The surface pressure and surface viscosity of monolayers of various unsaturated fatty acids at air/water interface were investigated at various temperatures. The unsaturated fatty acids used here were oleic acid (18 : 1), linoleic acid (18 : 2), linolenic acid (18 : 3), arachidonic acid (20 : 4), EPA (20 : 5), and DHA (22 : 6). Within the temperatures used, all the fatty acids formed expanded films, and their molecular areas (limiting areas) decreased with increase in temperature. Limiting area increased with the degree of unsaturation for fatty acids at the same temperature. The surface viscosity of the monolayer increased with the degree of unsaturation of fatty acids, and decreased with increasing temperature. The structure of monolayers of unsaturated fatty acids was found to depend on interactions between double bonds in unsaturated fatty acids and water molecules at the air/water interface.
