PHASE-TRANSITION OF POLYACRYLAMIDE GELS IN PEG SOLUTIONS

Non-ionic polyacrylamide gels immersed in aqueous solutions of poly(et hylene glycol) (PEG) exhibit a continuous volume change upon continuou s increase of the PEG concentration in the external solution. The volu me change becomes discontinuous when ionizable groups are incorporated into the network. As the proportion of ionizable groups increases, or , as the molecular weight of PEG decreases, the critical concentration of PEG required for a discontinuous volume collapse rises. The distri bution of PEG inside and outside the gel phase changes with gel volume ; it also exhibits a discontinuous change at the phase transition. Flo ry-Huggins theory gives a qualitative description of the phenomenon. ( C) 1997 Elsevier Science Limited.