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

Poly(N-isopropylacrylamide) (PNIPAM) precipitates out of water around 32 de grees C. This critical temperature is raised when hydrophilic acrylamide se quences are present on the polymer chain. We have used neutron scattering t o study the structural properties of a statistical copolymer containing acr ylamide and N-isopropylacrylamide segments at different temperatures and it s 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 clos e to the critical temperature of the copolymer, microphase separation is ob served. Here, the structure consists of dense nodules of hydrophobic sequen ces stabilized by hydrophilic sequences. In the presence of a small amount of SDS, additional colloidal stability is observed: the nodule size is decr eased. At high SDS concentration, the copolymer is completely solubilized a t all temperatures studied and the structure of the polymer-surfactant comp lex resembles the "necklace" structure obtained for the homopolymer PNIPAM- SDS system.