Interactions of sodium dodecyl sulfate with acrylamide -: N-isopropylacrylamide) statistical copolymer

Poly(N-isopropylacrylamide) (PNIPAM) precipitates out of water around 32 degrees C. This critical temperature is raised when hydrophilic acrylamide sequences are present on the polymer chain. We have used neutron scattering to study the structural properties of a statistical copolymer containing acrylamide and N-isopropylacrylamide segments at different temperatures and its interactions with an anionic surfactant, sodium dodecyl sulfate (SDS). At low temperatures, the copolymer behaves as a swollen polymer coil. With an increase in temperature, intermolecular attractions are observed, and close to the critical temperature of the copolymer, microphase separation is observed. Here, the structure consists of dense nodules of hydrophobic sequences stabilized by hydrophilic sequences. In the presence of a small amount of SDS, additional colloidal stability is observed: the nodule size is decreased. At high SDS concentration, the copolymer is completely solubilized at all temperatures studied and the structure of the polymer-surfactant complex resembles the "necklace" structure obtained for the homopolymer PNIPAM-SDS system.