Bulk and interfacial physical properties of aqueous solutions of sodium lauryl sulphate and lauryl alcohol. Part III: The effect of impurities and additives on pH and electrical conductance of premicellar and micellar solutions of sodium lauryl sulphate

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Abstract
Experimental measurements of the pH, electrical conductance and Kraft temperatures were made for a number of commercially available and purified samples of sodium lauryl sulphate for a wide range of surfactant concentrations in aqueous solutiin at 25°C. The efect of lauryl alcohol and sodium chloride on the pH and electrical conductance was also studied. The effects of type of electrodes, sequence of measurements, the memory effect, mixing and carbon dioxide were explored for the pH measurements. The results show that pH is a convenient and reliable method for the determination of critical micelle concentration (CMC) of ionic surfactants.The pH versus concentration data can also be used to uniquely identify the presence of contaminants or species other than pure sodium lauryl sulphate in that discontinuities occur in the data at unique concentrations so that identification of the contaminant is easy. High concentration discontinuities are identified and are attributed to individual or mixture CMC values. Anomalies in the data occur for concentrations less than 0.05 wt.% and especially around 0.01 to 0.02 wt.% for pure sodium lauryl sulphate solutions.Data are also given that show the effects of aging. Data reported in the literature for the pH, electrical conductance and Kraft temperature are compared.

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