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

•The idea of balance of density, compressibility, stretchability, mechanical strength was reported.•The additives like MWCNTs and silicone oil based thinners were added to silicone rubber for achieving such balanced properties.•Strain sensing tests shows good sensitivity (0.29 < GF < 0.95), a wide detection range (0 % < Δε < 40 %), and great linearity (0.998 < R2 < 0.949).•The stretchability of the 143% (control), 159% (MWCNTs) and 200% for 10 phr thinner (T10 sample).•At 10 phr thinner, the best mechanical stability was achieved while strain sensing was best for 2 phr MWCNTs in SR composites. 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. [Display omitted]