Solubilization of hydrophobic alcohols in aqueous Pluronic solutions: investigating the role of dehydration of the micellar core in tuning the restructuring and growth of Pluronic micelles

Abstract

Pluronics® are considered to be good carriers for poorly water soluble substances on account of their superior solubilization capacity over other ionic and nonionic surfactants. Understanding the influence of these substances on the aggregation characteristics of Pluronics® is therefore of overriding importance. In this manuscript we report dynamic light scattering, small angle neutron scattering, fluorescence and viscometry studies on the effect of adding hydrophobic alcohols viz. hexan-1-ol, octan-1-ol and decan-1-ol to the aqueous solutions of two Pluronics® (P85 and P123) with different hydrophilic–lipophilic balances. Both these Pluronics® exhibit a sphere to rod micellar shape transition with increasing temperature, the dynamics of the transition being significantly slower in the case of P123 because of its higher hydrophobicity and molecular weight. The aim of our studies was to investigate the restructuring and growth of Pluronic® micelles upon addition of hydrophobic alcohols that have applications in fields ranging from personal care/food products to pharmaceutical formulations. The studies show that alcohol induced micellar restructuring and growth for the two Pluronics® slow down as the concentration of alcohol increases and in addition their aqueous solubility decreases progressively from hexan-1-ol to decan-1-ol. These observations, which were manifested by a decreasing rate of sphere to rod micellar growth, have been attributed to more effective dehydration of the micellar core by alcohols with higher levels of solubilization and hydrophobicity. The results thus shed light on the specific role of additive induced dehydration of micellar cores in the restructuring and growth characteristics of micelles, for both hydrophilic (P85) and hydrophobic (P123) Pluronics®.