Critical points of the volume phase transition in N-isopropylacrylamide gels

Abstract

Two critical points of the gel–gel transition in N‐isopropylacrylamide gels were determined on the basis of the measurement of the coexistence curve. One of them was realized by changing the composition of solvent (water–methanol mixture) and the other by applying the osmotic pressure to a gel network, which was generated by adding large molecules to the outer solution. From the result the phase diagram in the x_m(solvent composition)–T(temperature)–π(osmotic pressure) space was constructed. The order parameter of the gel–gel transition was determined for the first time as functions of temperature and solvent composition. The existence of the critical points was discussed in terms of recent theoretical studies.