Cation–surfactant interactions in aqueous alkylphenoxypolyoxyethylene salt solutions. A Raman spectroscopic study

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Abstract
Raman difference spectroscopy has been employed to elucidate the effect of the alkali-metal (Li+, Na+, K+, Rb+ and Cs+) and alkaline-earth-metal cations (Mg2+, Ca2+, Sr2+ and Ba2+) on the polyether chain conformations of alkylphenoxypolyoxyethylene-type surfactants, C8H17Ph(CH2CH2O)ñOH where ñ= 9.5, in aqueous media. A band appeared at ca. 868 cm–1 in the spectrum of the surfactant upon the addition of some cations: this feature is assigned to a surfactant–cation complex incorporating a polyether chain exhibiting a TTGTT text-decoration:overlineG(T, trans; G; gauche; text-decoration:overlineG, gauche minus) or similar conformation sequence. The surfactant complexed preferentially to Ba2+ and K+, with the effect being greater for the former ion. A Ba2+ concentration-dependence study suggested that 1 : 2 and 1 : 3 surfactant–cation complexes are formed in the surfactant–water–salt system. The 1 : 3 coordinate complex appeared to be dominant. Models are proposed for the structure of these complexes.

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