METHOD OF MEASURING THE SWELLING PRESSURE OF SUPERABSORBENT GELS

A new experimental approach to the swelling pressure of polymer gels is proposed. In this method, a gel swells in a closed chamber with a flexible wall used as a force-measuring diaphragm. The swelling pressure is determined from the diaphragm deflection, which is evaluated from the number of Newton's rings formed between the diaphragm and the glass plate. This method allows precise determination of low pressures, from 0.1 to 20 kPa with the diaphragms used. The swelling pressure of ionic superabsorbent hydrogels based on polyacrylamide is measured as a function of the swelling degree and the ionic strength of the solution. A non-ionic polyethylene oxide hydrogel is also examined The experimental data agree with the results obtained by a conventional method. The swelling pressure is described by the theory that takes into consideration the network (Flory-Rehner) and ionic (Donnan) contributions.