Tough Double-Network Gels and Elastomers from the Nonprestretched First Network

Abstract

Double-network (DN) gels and elastomers, which consist of two (or more) rubbery polymer networks with contrasting physical properties, have received significant attention as they are extremely tough soft materials. The 1 st network of tough DN materials should be more brittle and weaker than the 2 nd network. In this paper, we reexamined the structural requirements of the covalently-cross-linked 1 st network of tough DN materials and established a non-prestretching strategy. While prestretching of network strands has been considered necessary for preparation of the brittle and weak 1 st network, we found that a non-prestretched network having a short strand length and low strand density can be used as the brittle and weak 1 st network for preparation of both tough DN gels and elastomers. This work can further expand the chemical and mechanical diversity of DN materials.

Chitin-Based Double-Network Hydrogel as Potential Superficial Soft-Tissue-Repairing Materials

“…Also, the high modulus of the DN hydrogel should favor the requirement for fibroblast activation and proliferation as previously reported. 26,67 In this work, the toughening strategy for the SN hydrogel referenced the pre-stretching strategy that had applied to the neutral polymer-based first network 45,68 , through introducing an additional flexible component to improve the network stretchability to obtain a higher swelling ratio for the fabrication of tough DN hydrogel. In various physiological saline and PBS buffer solutions, as well as in various pH solutions, the DN hydrogel deswelled very slightly (Table S1), which might be owing to the high osmotic pressure of the concentrated neutral PAAm in the DN hydrogels.…”

“…Also, another important factor to create a DN hydrogel is that the first network gets swell largely in the second network monomer solution. 45 The low aspect ratio of RCNs leads to the network brittleness and weakness 46 , which can fulfill the mechanical strength requirement as the first network in the double-network strategy.…”

A Review on Tough Soft Composites at Different Length Scales

“…As long as the concentration ratio between the first and second networks is carefully controlled, physical hydrogels with DN features can also be successfully fabricated. The DN method was firstly employed in the hydrogel systems and later proven to be applicable in elastomer systems [29,[48][49][50].…”

“…As long as the concentration ratio between the first and second networks is carefully controlled, physical hydrogels with DN features can also be successfully fabricated. The DN method was firstly employed in the hydrogel systems and later proven to be applicable in elastomer systems [29,[48][49][50]. The preparation of typical DN elastomers is slightly different from that of DN hydrogels since neutral monomers are commonly utilized to construct the first network.…”

Chain breaking in the statistical mechanical constitutive theory of polymer networks

“…Firstly, elastomers may be strengthened, toughened, and made more stretchable through the incorporation of one or more sacrificial networks that begin to break down irreversibly when stretched, dissipating energy while secondary networks maintain the integrity of the material. The sacrificial network is often embrittled as a swollen gel (Gong et al, 2003), but could also be pre-stretched using the secondary networks (Ducrot and Creton, 2016) or even designed without need for pre-stretching (Nakajima et al, 2019). The breaking in the sacrificial network may involve some additional functionality, such as mechanoluminescence (Ducrot et al, 2014) and recently, chain-lengthening (Wang et al, 2021).…”