Abstract
The temperature dependence of the enthalpy changes that accompany the addition of several surfactants to aqueous polyvinylpyrrolidone solutions was determined by titration calorimetry. The alkyl sulfates (octyl, decyl, and dodecyl) showed signs of binding, whereas the dodecylpyridinium halides (bromide and chloride), alkyldimethylphosphine oxides (decyl and dodecyl), and dodecylsarcosinate exhibited only a general solvent effect due to the presence of the polymer (that of a water structure-breaker). The binding of dodecyl sulfate was essentially athermal (although the heat of dilution was more endothermic due to increased dimicellization), and the binding of the octyl and decyl sulfates was endothermic near 25°C. At low dodecyl sulfate binding ratios, the monomeric form of the surfactant reacted with the polymer, but 2 3 of the surfactant was bound from the micellar state as saturation was approached. The differences between the binding properties of the various surfactants cannot be explained using existing theories of hydrophobic bonding.
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