Structure of Sodium Dodecyl Sulfate Bound to a Poly(NIPAM) Microgel Particle

Dynamic light scattering, small-angle neutron scattering, and binding isotherm measurements have been performed on an aqueous poly(N-isopropylacrylamide) microgel particle in the presence of the surfactant sodium dodecyl sulfate (SDS). In the presence of the microgel, at concentrations just above the normal cmc the surfactant existed as small, polymer-bound aggregates of less than five monomer units rather than larger micelles. This is in stark contrast to other homopolymer/surfactant systems such as SDS/poly(ethylene oxide) where the polymer-bound micelles have structures similar to those of free micelles obtained without polymers. Both dynamic light scattering and small-angle neutron scattering measurements showed that the microgel swells in the presence of surfactant. Two surfactant concentrations (1% w/w and 0.3% w/w) were used for the neutron scattering experiments, and through selective deuteration of the solvent, the different components, either the poly(N-isopropylacrylamide) gel or the SDS, were rendered ‘invisible' to the neutrons.