Biomimetic, Interface-Free Stiffness-Gradient PDMS-Co-Polyimide-Based Soft Materials for Stretchable Electronics and Soft Robotics.

Soft materials play a pivotal role in the efficacy of stretchable electronics and soft robotics, and the interface between the soft devices and rigid counterparts is especially crucial to the overall performance. Herein, we develop polyimide-polydimethylsiloxane (PI-PDMS) copolymers that, in various ratios, combine on a molecular level to give a series of chemically similar materials with an extremely wide Young's modulus range starting from soft 2 MPa and transitioning to rigid polymers with up to 1500 MPa. Of particular significance is the copolymers' capacity to prepare seamless stiffness gradients, as evidenced by strain distribution analyses of gradient materials, due to them being unified on a molecular level. The copolymers and gradient materials were successfully used as substrates for stretchable thin-film conductors and tested as dielectric elastomer actuators, demonstrating their potential application as enabling components in stretchable electronics and soft robots.