Submicellar aggregates in aqueous sodium dodecyl sulphate solutions: Investigations by dynamic light scattering and water penetration through porous media

Aqueous solutions of sodium dodecyl sulphate (SDS) are investigated by dynamic light scattering (DLS) and water penetration/wettability in porous hydrophobic chalk. The polydispersity index (PDI) and wettability are correlated with change in the population density of submicellar fragments. It is concluded that the number of submicellar fragments in aqueous surfactant solution is significantly reduced as a function of SDS concentration and in presence of different additives, namely sodium chloride (NaCl), dodecanol (C₁₂OH) and dodecyl trimethyl ammonium bromide (C₁₂TAB). The decrease in wettability and changes in polydispersity index (PDI) of micelles is correlated with the concentration of submicellar aggregates in aqueous solutions. The decrease in PDI as observed by DLS is a result of formation of stable micelles and subsequent reduction in population of submicellar aggregates. The water penetration in dustless chalk is primarily controlled by the rate of diffusion and subsequent adsorption of submicellar aggregates to the porous capillaries. With formation of stable micelles and reduction in number of submicellar aggregates, a peculiar reduction in water penetration is noted. The observed trend is described in terms of concentration of submicellar fragments under different conditions of surfactant solution.