Viscometry—a useful tool for studying conformational changes of poly(N-isopropylacrylamide) in solutions

Viscosity measurements as a function of temperature were used to characterize the phase transition when aqueous poly(N-isopropylacrylamide), poly(NIPAM), was heated past the lower critical solution temperature, LCST, at 32°C. Upon heating, the viscosity showed a large increase as the LCST was approached; this was attributed to intermolecular aggregation increasing the effective molecular weight of the polymer in solution. Beyond the LCST, reduction of viscosity was observed which is consistent with the viscometric properties of a diluted dispersion of colloidal particles.