f > 0.525 due to the large charge imbalance which is induced by the counterion
osmotic effect of the net polymer charges and the polymer segments elongate. And at
the very narrow region at f ¼ 0.51–0.525, the gels shrink (Q v < 1) as the Coulomb
attraction prevails over the repulsion for neutral polyampholytes and the polymers
collapse to a globule state (Fig. 3). The corresponding fracture stress dramatically
increases at this region and reaches a maximum value at f ¼ 0.52. The optimized
tough gel has ~50 wt% water content, which is quite close to that of biological
tissues but lower than those of conventional hydrogels (>80 wt%). It was confirmed
that the gel prepared from the precursor solution at f ¼ 0.52 has an exactly balanced
charge ( f true ¼ 0.5) by element analysis [52].
2.2 Total Ionic Monomer Concentration
Secondly, PA gel P(NaSS-co-DMAEA-Q) with various monomer concentration C m
was prepared at f ¼ 0.52 without any chemical cross-linkers. When the sample was
synthesized at low C m (<1.2 M), precipitation or phase separation occurs, indicating
Fig. 3 The effect of NaSS
molar fraction on the
volume swelling ratio, the
weight swelling ratio,
Young’s modulus, and
compressive fracture stress
of PA hydrogel P(NaSS-coDMAEA-Q) 2.0-f-0.1%.
Reproduced with
permission from Ref. [52]
300
T. L. Sun and K. Cui
osmotic effect of the net polymer charges and the polymer segments elongate. And at
the very narrow region at f ¼ 0.51–0.525, the gels shrink (Q v < 1) as the Coulomb
attraction prevails over the repulsion for neutral polyampholytes and the polymers
collapse to a globule state (Fig. 3). The corresponding fracture stress dramatically
increases at this region and reaches a maximum value at f ¼ 0.52. The optimized
tough gel has ~50 wt% water content, which is quite close to that of biological
tissues but lower than those of conventional hydrogels (>80 wt%). It was confirmed
that the gel prepared from the precursor solution at f ¼ 0.52 has an exactly balanced
charge ( f true ¼ 0.5) by element analysis [52].
2.2 Total Ionic Monomer Concentration
Secondly, PA gel P(NaSS-co-DMAEA-Q) with various monomer concentration C m
was prepared at f ¼ 0.52 without any chemical cross-linkers. When the sample was
synthesized at low C m (<1.2 M), precipitation or phase separation occurs, indicating
Fig. 3 The effect of NaSS
molar fraction on the
volume swelling ratio, the
weight swelling ratio,
Young’s modulus, and
compressive fracture stress
of PA hydrogel P(NaSS-coDMAEA-Q) 2.0-f-0.1%.
Reproduced with
permission from Ref. [52]
300
T. L. Sun and K. Cui