Evaluation of micellar properties of sodium dodecylbenzene sulphonate in the presence of some salts

Abstract

The influence of some salts (NaCl, KCl, $$\hbox {NH}_{4}$$ Cl and $$\hbox {MgCl}_{2})$$ on the critical micelle concentration (CMC) and fraction of counterion dissociation ( $$\alpha $$ ) of sodium dodecylbenzene sulphonate (SDBS) have been determined by conductometric and dynamic light scattering (DLS) methods at 298.15 K. The CMC determination involves fitting of experimental conductivity-surfactant concentration data into the integral form of Boltzmann-type sigmoidal equation. The procedure provides much better results compared to the conventional and differential methods for surfactant such as SDBS that exhibits a gradual transition from pre-micellar to the post-micellar region. The decrease in CMC of SDBS was found to be the highest in the presence of $$\hbox {MgCl}_{2}$$ and least in the case of NaCl among the studied salts. The fraction of counter ion dissociation decreases sharply at lower concentrations of the salts (except NaCl) which have been discussed in terms of effective ionic charge on the micelles. Using CMC and $$\alpha $$ value, the aggregation number of the micelle, micellar surface area and packing parameter has been calculated and were seen to agree well with the corresponding literature values obtained by using fluorescence and surface tension measurements. The effect of salts on the change in micellar size and the surface charge has also been evaluated with the help of DLS experiments and transmission electron microscopy (TEM) images. Synopsis:Precise and iterative procedure was used to calculate the critical micelle concentration and fraction of counter ion dissociation of SDBS micelles in the presence of salts.