ENTROPY OF ADSORPTION OF MIXED SURFACTANTS FROM SOLUTIONS ONTO THE AIR WATER INTERFACE/

The partial molar entropy change for mixed surfactant molecules adsorb ed from solution at the air/water interface has been investigated by s urface thermodynamics based upon the experimental surface tension isot herms at various temperatures. Results for different surfactant mixtur es of sodium dodecyl sulfate and sodium tetradecyl sulfate, decylpyrid inium chloride and sodium alkylsulfonates have shown that the partial molar entropy changes for adsorption of the mixed surfactants were gen erally negative and decreased with increasing adsorption to a minimum near the maximum adsorption and then increased abruptly. The entropy d ecrease can be explained by the adsorption-orientation of surfactant m olecules in the adsorbed monolayer and the abrupt entropy increase at the maximum adsorption is possibly due to the strong repulsion between the adsorbed molecules.