Conductance method study on the swelling kinetics of the superabsorbent

By measuring the conductance evolution of the sodium chloride (NaCl) aqueous solution during the superabsorbent swelling in it, a monotonic increasing cubic function, between the changes of sodium chloride molar number (Δn) in 1 m3 swelling medium and swelling ratios (Q) of the superabsorbent was discovered. Based on the relationship between Δn and Q, a monotonic increasing quasi cubic function between the conductance change (GC) and Q was deduced, which was verified by experiments. Therefore, the swelling kinetics of the superabsorbent could be tracked by testing GC of swelling medium. The results showed that the conductance method was in accordance with the tea-bag weight method. It was found by regression analysis that the concentration of NaCl in the hydrogel was lower than that of in the primitive solution—0.9 wt%, and the entrance of Na+ and Cl− was lagged behind. The latter was also verified by swelling phenomena of the superabsorbent in CuCl2 aqueous solution. Based on the results of our experiments, a swelling kinetic model for the superabsorbent was put forward.