Manipulation of Concentration-Conductivity Data of Sodium Dodecyl Sulphate and Sodium Dodecylbenzene Sulphonate in KCl Solution in Relation to Micellisation Parameters

Abstract

The conductivity of sodium dodecyl sulphate (SDS) and sodium dodecylbenzenesulphonate (SDBS) has been studied in varying concentrations (0-5 mM) of aqueous KCl solution at 25oC. Data analysis was based on the conventional treatment of conductivity-concentration data, differential, and integration methods with the aim of knowing the best method. As expected, the conductivity increased with an increase in surfactant concentration; the plot of which showed a kink at critical micelle concentration, cmc (i.e. point of aggregation). The results showed no apparent relationship between the degree of counterion binding, β and [KCl]; and an inverse relationship between the cmc values and [KCl]. β was within 0.4-0.6 for SDS and 0.1-0.3 for SDBS. The cmc of SDS decreased from ca. 8 to 6 mM and that of SDBS from ca. 2 to 1 mM as the [KCl] increased from 0-5 mM. These values are in mutual agreement irrespective of the method used. It was confirmed that in the absence of KCl, values obtained from the integration method were more consistent with those reported in the literature; therefore this method is recommended as the best method for determination of micellisation parameters provided the process is followed by conductivity measurements.