Time-resolved fluorescence anisotropy studies of the interaction of N-isopropyl acrylamide based polymers with sodium dodecyl sulphate

Time-resolved anisotropy measurements have been used to probe the interaction between poly(N-isopropylacrylamide), PNIPAM, and sodium dodecyl sulphate, SDS, in aqueous solution. Investigation of the intramolecular segmental dynamics of an acenaphthylene labelled sample, ACE-PNIPAM, below the lower critical solution temperature, LCST, has revealed that at the critical aggregation concentration, CAC, the polymer changes its conformation from an expanded water swollen structure to a surfactant swollen coil of reduced mobility. At temperatures in excess of the LCST, addition of SDS to ACE-PNIPAM induces a change in macromolecular shape from a collapsed globule to an expanded surfactant swollen coil. The presence of SDS at concentrations in excess of the CAC elevates the temperature of the conformational transition and corresponding LCST.The CAC was observed to decrease as a function of hydrophobic modification of PNIPAM. This was considered to reflect hydrophobic cavity formation between styrene units in the copolymer samples which enhance aggregation with SDS.