Recent Progress in Double Network Elastomers: One Plus One is Greater Than Two

Human beings cannot live without elastomers, which exist almost everywhere in human life nowadays. Although elastomers with a variety of features are developed for specific applications, a timeless topic is how to toughen them, because mechanical properties always determine the reliability and lifespan of the utilized elastomers. Toughening of a soft material has a long history and the main idea is widely accepted, i.e., building energy dissipation into the stretchy networks. Double network (DN) method is the most pioneering and representative practice of materials toughening, which is successfully applied to numerous hydrogel systems. Intensive studies on DN hydrogel systems are implemented and relevant reviews are well documented, whereas important reviews about DN elastomers are absent. In this review, recent progress on toughening elastomers using the DN strategy is reviewed. By reviewing the fabrication methods and relevant extensions, toughening mechanisms at different length scales, functionalities, and applications in sequence, it is shown how one polymer network plus another gives rise to a tough elastomer with superior mechanical properties. It is believed that this review can give some insight into existing DN elastomer systems and inspire the development of next-generation tough soft materials.