Stress Relaxation of Poly ( N-isopropylacrylamide) Gels in the Collapsed State

Abstract

Stress relaxation behavior of poly ( N-isopropylacrylamide)(PNIPA) gels in the collapsed state was investigated. The normalized stress reduction ( Δσ_eo/σ_eo) decreased with increasing temperature. The higher value of Δσ_eo/σ_eo was observed for the gels prepared from the solution with high monomer concentration ( c₀ ). The relaxation time determined in the long time region of the stress relaxation curve ( τ_σ) become shorter as temperature increases. The longest relaxation time τ_σ decreased with increasing c₀. It was also shown that the diffusion constant of the network in the collapsed state is much smaller compared with that in the swollen state.