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Anionic surfactant precipitation in hard water

1987; Elsevier BV; Volume: 115; Issue: 1 Linguagem: Inglês

10.1016/0021-9797(87)90006-3

1095-7103

Christine Noı̈k, M. Bavière, D. Defives,

Thermodynamic properties of mixtures

The precipitation of sodium p-(1-propylnonyl)benzene sulfonate by sodium and calcium ions, with or without n-butanol, has been studied at 25°C. Experiments corroborate the fact that the solubility of the surfactant in sodium and calcium solutions increases with the electrolyte content above the critical micelle concentration. Nevertheless, in sodium chloride and/or alcohol solutions this increase in salt tolerance does not coincide with the onset of micellization. To interpret the isotherm curves of precipitation, a thermodynamic model based on the electrical double-layer theory has been used, with micelles being considered as a separate phase. Reasonable agreement between theory and experiments is obtained by assuming a variation in the surface charge density of the micelles with the mole fraction of calcium ions. The behavior of surfactant solutions near the precipitation boundaries has also been characterized by viscosity measurements.