Polymeric micelle disruption by cosolvents and anionic surfactants

► Pluronic P123 and SDS interact very strongly forming mixed micelles. ► SANS shows the aggregation number of the mixed micelle decreases with both ethanol and SDS. ► At low SDS/P123 ratios, the principle structure resembles a P123 micelle. ► At high SDS/P123 ratios, SDS-rich micelles are present. Polymeric surfactants are frequently used to solubilise sparingly water soluble additives, often in conjunction with non-polymeric surfactants and cosolvents. Here, the structure of micelles formed by one such polymeric surfactant, Pluronic P123, have been characterised in the presence of the anionic surfactant sodium dodecylsulphate (SDS) and ethanol. In binary mixtures, with increasing ethanol concentration, the critical micelle concentration (CMC) of P123 increases whereas that for SDS decreases, yet the aggregation number of both micelles decrease. In the ternary system the effects of the ethanol on the mixed P123/SDS micelle are non-specific, merely moderating the behaviour to reflect the solvent polarity, except at low P123 concentrations where the addition of the anionic surfactant disrupts the structure of the polymeric micelle. This study into polymer/surfactant complexation in the presence of cosolvents highlights the complex behaviour of formulated products.