this demonstrated that WSC-g-PAA/PVA/NP
was stimuli-responsive to the pH. This pH stimuli-responsive property
was mainly attributed to the protonation of carboxylate anions
under an acidic circumstance, which could lead to the disappearance
of anion-anion repulsion. Furthermore, the hydrogen-bonding interaction
among hydrophilic groups was also reinforced because of the
protonation. At the same time the physical crosslinking degree of
skeleton network was also heightened, resulting from the relatively
lower water holding capacities. With the sustained increasing pH,
both the negative effect of H+ on electrostatic repulsive force and
the hydrogen-bonding interaction among carboxylate groups were
weakened by degrees and as a result more water could be absorbed
by WSC-g-PAA/PVA/NP. However, excessive Na+ in the immersion solution
could screen the charges of −COO− groups (so called “charge
shielding effect”). This process would weaken the electrostatic repulsion,
consequently, the swelling capacities declined with increasing
pH from 7 to
this demonstrated that WSC-g-PAA/PVA/NPwas stimuli-responsive to the pH. This pH stimuli-responsive propertywas mainly attributed to the protonation of carboxylate anionsunder an acidic circumstance, which could lead to the disappearanceof anion-anion repulsion. Furthermore, the hydrogen-bonding interactionamong hydrophilic groups was also reinforced because of theprotonation. At the same time the physical crosslinking degree ofskeleton network was also heightened, resulting from the relativelylower water holding capacities. With the sustained increasing pH,both the negative effect of H+ on electrostatic repulsive force andthe hydrogen-bonding interaction among carboxylate groups wereweakened by degrees and as a result more water could be absorbedby WSC-g-PAA/PVA/NP. However, excessive Na+ in the immersion solutioncould screen the charges of −COO− groups (so called “chargeshielding effect”). This process would weaken the electrostatic repulsion,consequently, the swelling capacities declined with increasingpH from 7 to
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