Equilibrium swelling curves of N-isopropylacrylamide (NIPA) gel and a series of its ionized counterparts were measured as a function of temperature. Nonionic NIPA gels underwent a sharp yet continuous volume change, whereas incorporation of a small amount of ionizable groups into the gel network drives the transition toward a discontinuous one. The critical ionic concentration and polymer network density at which the get undergoes a critical phase transition were determined. The results were analyzed using a mean field theory. Discrepancy between experimental data and theory is nontrivial, and may require the formulation of a more elaborate theory.

Erratum: Extended diffusion of rigid asymmetric molecules [J. ERRATA Erratum: Sticky electrolyte mixtures in the Percus-Yevick/mean spherical approximation [J. Chem. Phys. 94, 5077 (1991)]

No abstract

Nonionic N-isopropylacrylamide gel was found to undergo a discontinuous phase transition by changing a solvent composition or temperature. The observation that polymer gel with and without charge can undergo a first order volume phase transition is an evidence for the universality of the phase transition of polymer gels.

No abstract