The adsorption at water/hexane interface and micelle formation of dodecyltrimethylammonium chloride (DTAC) were studied by measuring its interfacial tension as a function of temperature under atmospheric pressure at various concentrations around the critical micelle concentration (cmc). By applying the thermodynamic equations developed previously, the entropy and energy changes associated with the adsorption from monomeric and micellar states were estimated and compared with those of the DTAC solution-air system. It was found that the entropy and energy of the adsorbed film of DTAC are remarkably depressed by the coexistent hexane phase. This finding explains the positive entropy change associated with the adsorption of DTAC at water/air interface.
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