A phase diagram of neutral polyampholyte – from solution to tough hydrogel (original) (raw)

2013, Journal of Materials Chemistry B

Our recent study has revealed that neutral polyampholytes form tough physical hydrogels above a critical concentration C m,c by forming ionic bonds of wide strength distribution. In this work, we systematically investigate the behavior of a polyampholyte system, poly(NaSS-co-DMAEA-Q), randomly copolymerized from oppositely charged monomers, sodium p-styrenesulfonate (NaSS) and acryloyloxethyltrimethylammonium chloride (DMAEA-Q) without and with a slight chemical cross-linking. A phase diagram of formulation has been constructed in the space of monomer concentration C m and cross-linker density C MBAA. Three phases are observed for the as-synthesized samples: homogeneous solution at dilute C m , phase separation at semi-dilute C m , and homogenous gel at concentrated C m. Above a critical C m,c , the polyampholyte forms supramolecular hydrogel with high toughness by dialysis of the mobile counter-ions, which substantially stabilizes both the intraand inter chain ionic bonds. Presence of chemical cross-linker (C MBAA >0) brings about a shift of the tough gel phase to lower C m, c. The tough polyampholyte gel, containing ~ 50wt% water, is highly stretchable and tough, exhibits fracture stress of σ b ~ 0.4 MPa, fracture strain of ε b ~ 30, and the work of extension at fracture ~ 4 MJ/m 3. These values are in the level of most tough soft materials. 3 Owing to the reversible ion bonds, the poly(NaSS-co-DMAEA-Q) gels also exhibit complete self-recovery (100%) and high fatigue resistance upon repeated large deformation.