SDS triggered transformation of highly hydrophobic Pluronics® nanoaggregate into polymer-rich and surfactant-rich mixed micelles

Abstract

This work reveals the role of sodium dodecylsulphate (SDS, anionic surfactant) in altering the phase behaviour and aggregation characteristics of five very hydrophobic polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymers containing 10% PEO but with different molecular weight. These copolymers are molecularly dissolved in water at ≤15–20 °C and exist as unstable vesicular structure at temperature close to cloud point (CP) >20 °C. SDS enhanced the aqueous solubility and CP of copolymers in water; progressive addition of SDS triggered the transformation of unstable vesicles into spherical mixed micelles. A correlation between the molecular orbital energy levels of Pluronics® and SDS is well comprehended using computational simulation approach where the perception of SDS stabilized Pluronics® micelles is predicted and correlated with optimized parameters. The size/ shape of copolymer-surfactant mixed nanoscale aggregates was evaluated using dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The scattering studies showed the presence of spherical mixed aggregates, whose size expanded with increase in hydrophobicity of Pluronics®. In high SDS concentration regime, SANS analysis uncovered the diminishing size of vesicles into spherical mixed aggregates. The nanoscale Pluronics®-SDS mixed micelles remained stable in water where this investigation discloses the conceivable ability of orange-OT solubilization using UV–vis spectroscopy.