The Effects of Organic Additives on the Solubilities and CMC’s of Potassium Alkyl Sulfates in Water. II. Effects of Some Nonhydroxy Compounds

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Abstract
Solubilities and critical micelle concentrations (CMC) of potassium dodecyl sulfate (KDS) and hexadecyl sulfate (KHS) were measured in aqueous solutions to which dioxane, acetone, urea, or dimethyl sulfoxide had been added over the temperature range of 5–40°C. It was found that all additives mentioned above raised solubility and CMC with an exception for dioxane which showed a slight minimum on a CMC-additive concentration curve. Solvent effects on the alkyl and ionic groups of a surfactant molecule were separated by considering the difference of the standard free energy change for the solution process of KHS and that of KDS. It was deduced that a primary effect on the alkyl group is the one that a strongly cohesive solvent, water, is replaced by a less cohesive organic solvent and other mechamisms, such as an effect on the water structure, follow as the secondary. In terms of the above considerations, effects on the Krafft point were also referred to.