Sclerox-chitosan co-gels: Effects of charge density on swelling of gels inionic aqueous solution and in poor solvents, and on the rehydration of dried gels

The equilibrium volumes of swollen carboxylated scleroglucan (sclerox) gels crosslinked with chitosan, were studied as function of salt concentration, salt type, pH and solvent composition. The degrees of carboxylation of scl erox were D-car = 0.0-0.3. The ratio between the equilibrium volume of the swollen gel and the reference volume, V/V-o showed a dependence on NaCl con centration in aqueous solvents for the various D-car that conformed well to the theory for swelling of polyelectrolyte networks. Also the dependence o f V/V-o on the valence of the simple electrolyte predicted by this theory w as reproduced experimentally. In aqueous iso-propanol solutions without add ed electrolyte, the sclerox-chitosan gels collapsed for volume fractions of propanol, W-p, larger than 0.64. Increasing the imbalance ratio of the pol yampholyte sclerox - chitosan co-gels by increasing the fraction of chitosa n showed that V/V-o decreased for pH values where electrostatic attractions between NH: of chitosan and COO - were effective. The swelling behavior of rehydrated, dried gels showed qualitatively the same response to various s olvent conditions as the never dried gels, but there were minor quantitativ e differences. This study shows that sclerox-chitosan co-gels possessing po lyelectrolyte or polyampholyte nature can be made by varying the molecular parameters of the gels, and thereby control how these gels respond to vario us aqueous salt solutions. (C) 1999 Elsevier Science Ltd. All rights reserv ed.