Minima in Surface Tension–Concentration Curves of Solutions of Sodium Alcohol Sulfates.

Abstract

The observation of minima in the surface tension-concentration curves for aqueous solutions of various surface-active materials has been the cause of considerable conjecture. Pownev and Addison (12), in particular, found welldefined minima in the surface tension of solutions of sodium salts of primary alcohol sulfates containing from twelve to eighteen carbon atoms. The minima are as much as 5 dynes per centimeter lower than the value reached at higher concentrations. These "anomalous" results have presented apparent disagreement with Gibbs' adsorption equation. The hypotheses proposed to reconcile such incongruities have been frequently discussed (1 to 12).Usually the explanations proposed fall into two groups: First, it has been claimed that there are experimental difficulties which result in errors in the methods used for measuring surface tension (3, 4, 7). On the other hand, the possible existence of abrupt changes in colligative properties of solutions of certain surface-active substances has been emphasized ( 12) and this could lead to minima in the surface tension-concentration curves.The data which we present here deal with solutions and procedures not covered by either of the above explanations. PROCEDUREThe sulfated alcohols used in this work were of a particularly high degree of purity. The details of the methods used in their preparation are given in a report entitled "Some Properties Involving Surface Activity of Sodium Salts of Primar}* and Secondary Alcohol Sulfates" (5).

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Self-Phase-Stabilized Heterodyne Vibrational Sum Frequency Generation Microscopy

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Critical micelle concentrations of aqueous surfactant systems

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