Considering the influence of salts on the swelling of
hydrogels, the ionic pressure is an important factor which
is dependent on the concentrations of ions inside the
hydrogel (Ci.gel) and the medium (Ci.medium).
pion ¼ RTRðCi:gel Ci:mediumÞ: ð18Þ
Reductions observed in the FSC of the hydrogels in the saline
solution can be attributed to increase in Ci.medium which
reduced the osmotic pressure. Previous studies have also
confirmed the reduction of swelling capacity of hydrogels
in saline solution [26].
The effect of pH on the FSC is presented in Fig. 11. The
result shows that minimal swelling occurred in the buffer
solution at pH 4 and FSC increased when the studies were
conducted in alkaline media i.e. buffer solutions at pH 8
and 9. Swelling was facilitated at alkaline pH ranges because of the enhanced ionization of the carboxylate groups
on the hydrogel which promoted inter- and intramolecular
repulsions within the polymeric network. It is reasonable
that this development improved water absorption into
the hydrogel.