“…This interesting phase behavior of a dramatic dependence of the swelling volume on temperature and a discontinuous transition has attracted the interest of many researchers all over the world in past years. Studies on the thermodynamic behavior of this system (Marchetti et al, 1990;Sousa, 1993;Sousa, 1995;Nakamoto, et al, 1996), different potential applications (Wu et al, 1996;Jin, et al, 1995), and permeability to small solutes (Palasis & Gehrke, 1992;Mukae, et al, 1993) have been reported. The thermodynamics of polymer gels describes the swelling equilibrium as a result of two opposite contributions: the change in the free energy of mixing as the gel is in contact with a solvent and the change in the elastic free energy due to the elongation of the network as the gel swells, absorbing solvent (Ogata, 1995).…”