The surface tension of the aqueous solution of dodecylmethylammonium chloride (DMAC) and dodecyl-dimethylammonium chloride (DDAC) was measured as a function of temperature under atmospheric pressure at concentrations below and above the critical micelle concentration (cmc). The entropy and energy of adsorption from the monomeric state in the aqueous solution and the micellar state were evaluated by applying the thermodynamic equations of adsorption to the surface tension values. The thermodynamic quantities were compared with those of the aqueous solutions of dodecylammonium chloride (DAC) and dodecyltrimethylam-monium chloride (DTAC). It was found that the successive Af-methylation of DAC has a considerable effect on the adsorbed film with changes in its surface density, entropy, and energy brought about by changes in the geometry and the hydrophilicity of the polar head group.
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