Toughening Elastomer while Lowering Hysteresis Using Peptide Cross-Linkers

Various strategies were proposed to toughen elastomers; however, they usually result in high hysteresis, particularly for those toughened by introducing sacrificial bonds. To overcome the trade-off relationship between toughness and hysteresis, here poly(benzyl acrylate) elastomers were synthesized using poly(γ-benzyl- l -glutamate)-based peptide cross-linkers. The α-helical peptide segments introduced into the polymeric network act like molecule-sized springs. They absorb energy when loaded but return it when unloading. Therefore, the peptide-cross-linked elastomer exhibits enhanced toughness and simultaneously a lowered hysteresis. Besides high toughness and low hysteresis, the elastomer also presents high ductility (break strain: 4700%), flexibility, crack-insensitivity (fracture toughness: 1.25 × 10 4 J m –2 ), and fatigue resistance (fatigue threshold: 9.27 × 10 2 J m –2 ). In addition, the adhesive properties of the elastomer are also improved. The adhesion strength on polypropylene is up to 5.50× 10 2 kPa. Thirty days of immersion in water leads to only a small decrease in adhesion strength, demonstrating excellent long-term underwater adhesion stability. Taking advantage of the high toughness, low hysteresis, and excellent adhesion strength of the elastomer, a composite hydrogel strain sensor was designed. Human motion was successfully monitored both in the air and underwater.