Transformations of wormlike surfactant micelles induced by a water-soluble monomer

Abstract Hypothesis Wormlike surfactant micelles (WLMs) are prospective as nanoreactors for micellar copolymerization of hydrophilic and hydrophobic monomers. Hydrophilic monomers can destroy WLMs. Large size and cylindrical shape of micelles can be preserved by high salt content favoring closer packing of surfactant heads. Experiments The effect of a water-soluble monomer (acrylamide) on the structure and rheological properties of giant WLMs of an anionic surfactant potassium oleate at different salt content was investigated by combined experimental (SANS, rheometry, fluorescence and NMR spectroscopy, tensiometry) and molecular dynamics simulations studies. Findings At low salt content, when WLMs are linear, acrylamide induces their shortening and transformation into spherical micelles as a result of its incorporation into the micellar corona, leading to the drop of viscosity. At high salt content providing branched WLMs, monomer first triggers their transition to long linear chains, which enhances the viscoelasticity, and then to rods. This is the first report showing that the effect of monomer on the rheological properties is quite different for linear and branched micelles. Using branched micelles allows preserving large WLMs at high water-soluble monomer content, which is favorable for their use as nanoreactors for synthesis of copolymers with high degree of blockiness, which give mechanically tough polymer gels.