CONFORMATIONAL-CHANGES OF POLY(VINYLCAPROLACTAM) MACROMOLECULES AND THEIR COMPLEXES WITH IONIC SURFACTANTS IN AQUEOUS-SOLUTION

Dynamic light scattering measurements have been performed for aqueous solutions of linear poly(vinylcaprolactam) (PVCa) at several polymer c oncentrations and over a wide range of ionic surfactant concentration. The intermolecular aggregation of PVCa accompanied by a sharp increas e of the light scattering intensity is observed in pure water at 33 de grees C. The effect of ionic surfactants (cetylpyridinium chloride (CP C) and sodium dodecyl sulfate (SDS)) on the behavior of solutions of l inear PVCa was studied as a function of temperature. For polymer conce ntrations below the overlap concentration (2.5 mg/mL) a decrease of th e macromolecular hydrodynamic diameter is observed upon the addition o f ionic surfactant (SDS, CPC) at low surfactant concentrations. This e ffect is in contrast to the behavior of the complexes of surfactant wi th another thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPA ). A further increase of the surfactant concentration leads to the ree ntrant swelling of macromolecules. In the presence of ionic surfactant the temperature increase results in the sharp drop of the hydrodynami c diameter of the particles at some critical temperature. This critica l temperature becomes higher with increasing surfactant concentration. For higher polymer concentrations (5 mg/mL) the particle size always increases upon the addition of ionic surfactants, because of intermole cular aggregation.