Network formation in poly(N-isopropyl acrylamide)/water solutions during phase separation

Abstract Evidence from dynamic viscoelasticity measurements has been found for reversible network formation via the physical association of hydrophobic side-groups during phase separation at around 33°C in a 1.22 wt.% aqueous solution of poly( N -isopropyl acrylamide) (PNIPA) having a molecular weight of 2.1 × 10 6 . The frequency ω dependence of the dynamic storage and loss moduli G ′ and G ″ showed homogeneous fluid behaviour at 25°C, while at 35°C, a plateau zone was found in the G ′ versus ω curve and G ′ was larger than G ″, indicating the formation of a network. The increase in G ′ was instantaneous at the phase separation temperature and was not a progressive process.