SWELLING OF POLYACRYLAMIDE GELS IN POLYACRYLAMIDE SOLUTIONS

Swelling behavior of polyacrylamide (PAAm) and polyacrylamide-co-polya crylic acid (PAAm-co-PAAc) gels was investigated in aqueous solutions of monodisperse PAAms with molecular weights ((M) over bar(w)) ranging from 1.5 x 10(3) to 5 x 10(6) g/mol. The volume of the gels decreases as the PAAm concentration in the external solution increases. This de crease becomes more pronounced as the molecular weight of PAAm increas es. The classical Flory-Huggins (FH) theory correctly predicts the swe lling behavior of nonionic PAAm gels in PAAm solutions. The polymer-po lymer interaction parameter chi(23) was found to decrease as the molec ular weight of PAAm increases. The swelling behavior of PAAm-co-PAAc g els in PAAm solutions deviates from the predictions of the FH theory. This is probably due to the change of the ionization degree of AAc uni ts depending on the polymer concentration in the external solution. (C ) 1998 John Wiley & Sons, Inc.