Tailoring of Self-Healable Polydimethylsiloxane Films for Mechanical Energy Harvesting

Triboelectric nanogenerators (TENGs) have emerged as potential energy sources as they are capable of harvesting energy from low-frequency mechanical actions such as biological movements, moving parts of machines, mild wind, rain droplets, and others. However, periodic mechanical motion can have a detrimental effect on the triboelectric materials that constitute a TENG device. This study introduces a self-healable triboelectric layer consisting of Ecoflex-coated self-healable polydimethylsiloxane (SH-PDMS) polymer that can autonomously repair mechanical injury at room temperature and regain its functionality. Different compositions of bis(3-aminopropyl)-terminated PDMS and 1,3,5 triformyl benzene were used to synthesize SH-PDMS films to determine the optimum healing time. The SH-PDMS films contain reversible imine bonds that break when the material is damaged, and are subsequently restored by an autonomous healing process. However, the inherent stickiness of the SH-PDMS surface itself renders the material unsuitable for application in TENGs in spite of its attractive self-healing capability. We show that spin-coating a thin layer (≈30 µm) of Ecoflex on top of the SH-PDMS eliminates the stickiness issue while retaining functionality as a triboelectric material. TENGs based on Ecoflex/SH-PDMS and Nylon 6 films show excellent output and fatigue performance. Even after introducing incisions at several locations in the Ecoflex/SH-PDMS film, the TENG spontaneously attained its original output performance after a period of 24 h of healing. This study presents a viable approach to enhance the longevity of TENGs to harvest energy from continuous mechanical actions, paving the way for durable, self-healable mechanical energy harvesters.