Lightweight, compressible, stretchable, ultra-soft, and mechanically stable composites for piezo-electric energy generators and strain sensing

Abstract

Fabricating rubber composites with desired densities, compressibilities, stretchabilities, mechanical strengths, and self-healing properties is challenging. The present study focused on designing balanced properties, paying special attention to the mechanical stability required for piezo-electric energy generators for soft applications. To achieve these goals, silicone rubber (SR) was used as the host matrix, and multi-walled carbon nanotubes (MWCNTs) were used as the filler. MWCNTs were used as filler to reinforce composites and make them electrically conductive. Adding silicone oil as a thinner reduced compressive modulus and tensile strength but improved stretchability. The compressive modulus of the SR control was 1.86 MPa, and it increased to 3.29 MPa when 2 phr of MWCNTs were added. However, it was decreased sharply to 1.14 MPa when 30 % thinner was added (the T30 sample). Similarly, the stretchability of the SR control was 143 %, and it increased to 159 % and 200 % when 2 or 10 phr (the T10 sample) of MWCNTs were added, respectively. Biomechanical tests showed that a thumb pressure generated the highest output voltages of 4.2 and 4.31 mV at MWCNT contents of 2 and 10 phr, respectively. Finally, strain sensing tests on the 2 phr MWCNT sample show good sensitivity (0.29 < GF < 0.95), a wide detection range (0 % < Δε < 40 %), and excellent linearity (0.998 < R2 < 0.949). Overall, adding thinner up to 10 phr provided the best formulation for mechanical stability and robust performance with optimum energy generation and high stretchability.