RHEOLOGICAL PROPERTIES OF HIGHLY SWOLLEN HYDROGEL SUSPENSIONS

The shear rheology of diluted to concentrated suspensions of weakly cr oss-linked sodium polyacrylate hydrogels were investigated by concentr ic cylinder rheometry. The size of the swollen gel particles is depend ent on the initial size of the dry particle and on the nature of the a dded salt. Polyvalent salts are more efficient for contracting the swo llen particles than monovalent ones. When suspended in water or in mon ovalent salt solutions, the viscosity at low concentrations shows a be haviour very similar to the one of flexible polymer solutions. Below t he critical overlap concentration, the viscosity is independent of she ar rate. The intrinsic viscosity is very large, on the order of 10-15 dL/g. This is in agreement with the large size of these swollen partic les. Suspensions of such swollen gel particles are thus a good model f or extremely high molecular weight polymer solutions. In polyvalent sa lt solutions different behaviour of the viscosity curves versus concen tration was observed. This effect is caused by chemical cross-linking of the hydrogel by polyvalent ions. (C) 1994 John Wiley & Sons, Inc.