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Calculation of the coefficient in the gibbs equation for the adsorption of ionic surfactants from aqueous binary mixtures with nonionic surfactants

1982; Elsevier BV; Volume: 87; Issue: 2 Linguagem: Inglês

10.1016/0021-9797(82)90344-7

1095-7103

Xi Yuan Hua, Milton J. Rosen,

Analytical Chemistry and Chromatography

An equation was derived for calculating from surface tension data the value of n, the coefficient in the Gibbs adsorption equation for ionic surfactants, in binary aqueous mixtures of ionic with nonionic surfactants. Data are provided for the systems: C12H25SO3Na-C12H25(OC2H4)8OH, C12H25C5H5NBr-C12H25(OC2H4)8OH, and C12H25SO4Na-l-C8H17OH. The value of n for these systems in the absence of added electrolyte remains in the vicinity of 1 until the area per surfactant ion in the surface film reaches a value of about 1. nm2. Closer packing of the surfactant ion in the film produces an increase in the value of n into the range between 1 and 2. When the area per surfactant ion in the surface film is >2. nm2, the value of n may be reduced to < 1 in the case of anionic-nonionic mixtures. This is explained as being due to the weakly cationic character of the nonionic surfactant.