The effects of salinity and temperature on the behaviour of polyacrylamide gels

Polymer gels are capable of undergoing large volume changes under the influence of solvent composition and temperature. Studies have been conducted on the effects of salinity and temperature on hydrolysed polyacrylamide gels. Three salinities were investigated from 5 parts per thousand (ppt) to 35 ppt, which is approximately the salinity of natural seawater in temperate waters. For each of the salinities, the effect of temperature from 5°C to 40°C with 5°C increments was investigated. It was found that hydrolysed polyacrylamide gels shrank in all the solutions, this effect being most pronounced at the high salinity (35 ppt), with a smaller volume decrease noted in 20 ppt and 5 ppt salinities, respectively. The effect of temperature was minimal, with all solutions promoting a decreasing volume change as the temperature increased. The polyacrylamide gels remained whole in the experiments with no visible signs of degradation. The cyclical volumetric strain behaviour of the gels was also investigated by alternate exposure to saline solutions and distilled water. Cyclical swelling and deswelling of the gels was observed which, in some cases, was fully reversible.