Water-Induced Brittle-Ductile Transition of Double Network Hydrogels

Abstract

In the previous studies, we have developed double network hydrogels (DN gels) with extraordinarily high mechanical strength and toughness although the gels contain 90 wt % of water. In this study, we investigated the effect of water content on the mechanical behavior of the DN gel consists of poly(2acrylamido-2-methylpropanesulfonic acid) gels (PAMPS gels) as the first network and polyacrylamide gels (PAAm gels) as the second network. When the DN gel was dried gradually from its equilibrium swelling state (90 wt % water content), it exhibited a ductile behavior with a very high fracture stress and strain at an intermediate water content c (65 wt % < c < 75%), and then became brittle upon further decreasing in water content (c < 60 wt %). The behavior of the DN gel was compared with the corresponding single network gels, PAMPS and PAAm. It is found that at the intermediate water content, the fracture stress and strain of PAAm gel reached maximum, and the brittle-ductile change of DN gel upon with the change in water content was the results of the change in the mechanical properties of PAAm network.

A phase diagram of neutral polyampholyte – from solution to tough hydrogel

“…This value is quite close to that of biological tissues, 41 but much lower than that of the conventional hydrogels or DN gels that have a much higher water content (>85 wt%). 42 Hereafter, we investigated the effect of other structure parameters on the mechanical properties of the polyampholyte gels at the equi-molar monomer fraction f=0.52 Phase separation is a time dependent process and so whether it occurs will depend on the relative rates of polymerization and phase separation. So, strictly speaking, the phase diagram shown in Figure 2b is a kinetic diagram that depends on the polymerization kinetics.…”

Solvent and Ca2+ triggered robust and fast stress generation by ultrathin triple-network hydrogels

“…This result clearly demonstrates that solvent-triggered isometric stress generation of the TN gel results from the change of its modulus induced by the solvents. Young's modulus of the gel in water is dominated by the elasticity of the highly stretched PAMPS chains that are much rigid than Gaussian chains [28]. Deswelling of the gel in mixture solvent relaxes the stretched PAMPS chains and therefore softens the gel.…”

Advanced Shape Memory Technology to Reshape Product Design, Manufacturing and Recycling

“…For hydrogels, water may be utilized to tailor the shape memory/change behavior [9,20,21]. Self-healing has been realized in different types of polymeric materials [22][23][24].…”