SWELLING OF POLY(ETHYLENE OXIDE) HYDROGEL S

Poly(ethylene oxide) hydrogels showing high equilibrium swelling in wa ter (up to 255 ml/g) were prepared by gamma-irradiation (doses up to 0 .5 Mrad) of deaerated aqueous solutions of the polymer (solution conce ntration 0.27 - 3.0 g/dl). Swelling of the hydrogels in water and aque ous solutions of salts was examined and their elastic modulus (0.2 - 1 .5 kPa) was measured; the network density was assessed to be (0.8 - 5. 0) x X 10(-5) mol/cm3. In the case examined, in aqueous solutions of s alts (NaCl, K2SO4, MgSO4), the swelling was suppressed to a lesser ext ent than in the case of polyelectrolyte hydrogels. Thermodynamic inter pretation of the behavior observed in aqueous salt solutions is presen ted. An abnormal, frequently irreversible, decrease in equilibrium swe lling and an increase in elastic modulus were discovered to accompany the drying or ionic deswelling of the hydrogels. These features may be related to the appearance of new additional junctions/nodes due to cr ystallization of the network chains or to the nonphantom effects. The effects are much more conspicuous in initially lightly cross-linked-hy drogels.