Effects of interaction of ionic and nonionic surfactants on self-assembly of PEO-PPO-PEO triblock copolymer in aqueous solution.

We study the effects of interaction of surfactants on the self-assembly of a triblock copolymer in aqueous solution by measuring percolation transition temperature (T(p)), micellar size, zeta potential, and rheological properties. We use PEO-PPO-PEO triblock copolymer (Pluronics-F108) with anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB), and nonionic nonylphenolethoxylate (NP9) for our investigations. The addition of SDS in pluronics solution leads to a dramatic reduction in the viscoelastic properties, while it remains almost unaffected with CTAB and NP9. The 2 orders of magnitude decrease in the elastic modulus in the presence of SDS indicates a soft solid-like microstructure formed by aggregating self-assembled triblock polymers. Our results indicate a strong electrostatic barrier imparted by the headgroup of SDS at the core-corona interface that inhibits the formation of hexagonally packed layers of micelles and the packing order. The analysis of autocorrelation function at high concentrations of ionic surfactant indicates that pure surfactant micelles coexist with large intermicellar structures. With increasing surfactant concentration, the zeta potential of the pluronic micelle is found to decrease. These results suggest that the microstructure and elastic properties of block copolymer micelles can be tuned by varying the concentrations of ionic surfactant that enhances their potential in applications as nanocarriers for drug delivery systems.