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The double-network (DN) structure is a state-of-the-art strategy used for toughening soft materials. The challenge for widespread applications, however, is the difficulty in synthesizing the two interpenetrating networks with contrasting architecture, i.e., one network is brittle and sparse and the other is stretchable and dense. Such structures are formed to toughen hydrogels via two-step sequential synthesis of a highly swellable polyelectrolyte network and a subsequent stretchable network in aqueous media; however, this approach is not directly applicable for fabricating tough DN elastomers from low-polar polymers. Herein, we propose a polyelectrolyte approach to fabricate tough solvent-free DN elastomers comprising a hybridized brittle polyelectrolyte network and a stretchable low-polar polyacrylic network. Because polyelectrolyte networks swell significantly in high-dielectric media, the contrasting DN structure can be fabricated using an organic cosolvent with an extremely high dielectric constant. By removing the solvent, we obtained polyelectrolyte–elastomeric polyacrylate DN elastomers, which exhibit a moderate elastic modulus (∼1 MPa), distinct yielding, high strength (∼5 MPa nominal stress), and large stretchability (∼2000% strain) accompanied by strain-hardening and high fracture toughness (∼104 J m–2). The volume ratio of the two networks is a key parameter governing mechanical performance. This approach broadens polymer choices for developing robust elastomers.
Matsuda et al. (Mon,) studied this question.