THE EFFECT OF SURFACTANT MONOLAYERS ON THE HEAT-TRANSFER THROUGH AIR WATER AND OIL/WATER INTERFACES USING IR IMAGING TECHNIQUE/

An experimental investigation on the effect of surfactant monolayers o n the heat transfer through air/water and oil/water interfaces was car ried out by observing the changes of surface temperature with LR Imagi ng Radiometer (Model 760). The heat transfer resistance of various sin gle component and mixed monolayers at air/water and oil/water systems was studied. The results show that the surfactant monolayers introduce a noticeable heat transfer resistance to the heat transfer process ac ross the interface. The solid monolayers exhibit lower resistance to h eat transfer than the liquid monolayers at the oil/water interface. At air/water interface, the presence of monolayer decreases the evaporat ive cooling process and therefore increases the surface temperature ra pidly. However, the presence of a monolayer at oil/water interface inc reases the heat transfer resistance across the oil/water interface. He at transfer resistance increases as the chain length of fatty acid inc reases at the oil/water interface. The effects of phase-transition fro m a two-dimensional solid to the liquid state in cholesterol-arachidyl mixed monolayers was observed from the change in heat transfer resist ance of the monolayers at the oil/water interface. The optimum molecul ar packing at the 1:3 molecular ratio in mixed surfactant monolayers o f oleic acid-cholesterol and stearic acid-stearyl alcohol at the oil/w ater interface was also observed by this technique. (C) 1998 Academic Press.