Enthalpy-entropy compensation of micellization of ethoxylated nonyl-phenols

Abstract

The thermodynamics of micellization of non-ionic surfactants (ethoxylated nonyl-phenols with different chain length) was studied as a function of ethoxy group number, electrolyte concentration and type, and concentration of short-chain alcohols at different temperature. On the basis of the thermodynamic data the enthalpy/entropy correlation and the ΔH/ΔS compensation temperature were calculated to characterize the solvent-solute and solute-solute interaction. The experimental results have definitely proved that a well-defined correlation exists for all investigated systems and the compensation temperature is independent of the ethoxy group number and the presence of alcohols. The inorganic electrolytes, however, decrease theT _c compared to both alcohol-free and alcohol-containing systems, indicating the change in the mechanism of the micellization process. The new theoretical results significantly contribute to confirmation of the earlier conclusion concerning the stability and the structure of non-ionic surfactant solutions.