Phase separation behaviour of polymers in water. Temperature and surfactant effect

The phase separation behaviour of a sample of poly(N-vinyl-2-pyrrolidone) (PVP) in aqueous Na₂SO₄ (0.55 M) containing a surfactant, sodium dodecyl sulfate (SDS), is studied with temperature and surfactant concentration as independent variables. Without surfactant, the polymer exhibits a lower solution temperature (LCST) of 28 °C, above which it precipitates. At SDS concentrations of only 300 mg L^-1, aggregation is prevented and the behaviour of isolated polymer molecules can be studied. Measurements of hydrodynamic radius (R_H) and intrinsic viscosity [η] of PVP in Na₂SO₄ (0.55 M) have been performed by using Dynamic Light Scattering (DLS) and viscometry. From these results, a coil-to-globulule phase transition was detected as a function of temperature at constant SDS concentreation.