Module‐Assembled Elastomer Showing Large Strain Stiffening Capability and High Stretchability

Abstract

Elastomers are indispensable materials due to their flexible, stretchable, and elastic nature. However, the polymer network structure constituting an elastomer is generally inhomogeneous, limiting the performance of the material. Here, a highly stretchable elastomer with unprecedented strain‐stiffening capability is developed based on a highly homogeneous network structure enabled by a module assembly strategy. The elastomer is synthesized by efficient end‐linking of a star‐shaped aliphatic polyester precursor with a narrow molecular‐weight distribution. The resulting product shows high strength (≈26 MPa) and remarkable stretchability (stretch ratio at break ≈1900%), as well as good fatigue resistance and notch insensitivity. Moreover, it shows extraordinary strain‐stiffening capability (>2000‐fold increase in the apparent stiffness) that exceeds the performance of any existing soft material. These unique properties are due to strain‐induced ordering of the polymer chains in a uniformly stretched network, as revealed by in situ X‐ray scattering analyses. The utility of this great strain‐stiffening capability is demonstrated by realizing a simple variable stiffness actuator for soft robotics.

Molecular Clogging Organogels with Excellent Solvent Maintenance, Adjustable Modulus, and Advanced Mechanics for Impact Protection

“…X‐ray scattering techniques, including small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray scattering (WAXS), are widely used for the analysis of the microstructure of soft materials such as polymers and gels. [ 42‐45 ] The microstructures of the prepared cross‐linked polyurea and MC‐Gels were further analyzed using SAXS and WAXS to confirm if there is any possible microscopic phase separation within the MC‐Gels. The SAXS results show that the samples of cross‐linked polyurea and MC‐Gel are both highly homogeneous in the 1–10 nm scale, without any micro‐phase separation.…”

Structural Analysis of the Linear Elasticity of End-Cross-Linked Star Elastomers with a Number of Trapped Entanglements via Coarse-Grained Molecular Dynamics Simulations

“…Furuya and Koga performed simulations on free-radical copolymerization gels and analyzed the effective network and cross-links to confirm the validity of Langley’s formulation for various polymer densities and binding ratios. However, directly counting the entanglements between the effective network for tetra-/tri-PEG gel-like end-cross-linked star-shaped elastomers, ,, in which the number of trapped entanglements increases with the cross-linking reaction, with small number of loops, has not been performed.…”