Achieving highly electrical conductivity and piezoresistive sensitivity in polydimethylsiloxane/multi-walled carbon nanotube composites via the incorporation of silicon dioxide micro-particles

Conductive polydimethylsiloxane (PDMS) composites have attracted extensive attention worldwide due to its potential application on wearable electronics and strain sensors. In this work, silicon dioxide micro-particles (μ-SiO2) were added into the flexible PDMS/multi-walled carbon nanotubes (MWCNT) composites to improve their electrical conductivity and piezoresistive sensitivity. First, the μ-SiO2 particles can exhibit volume exclusion effect to dense MWCNT fillers in PDMS matrix, which leads to the high electrical conductivity and low percolation threshold. Furthermore, the larger μ-SiO2 particles could give higher electrical conductivity and lower percolation threshold. For examples, the electrical conductivity and percolation threshold of the PDMS/MWCNT composites with 0.3 vol% MWCNT increased from 3.5 × 10−9 to 2.2 × 10−4 S/m and decreased from 0.44 to 0.08 vol%, respectively, by the incorporation of 30 vol% 85 μm-SiO2 particles. Second, the piezoresistive sensitivity of PDMS/MWCNT composites was abruptly enhanced by the addition of μ-SiO2 particles because of the high modulus of μ-SiO2 particles, which resulted in the asymmetric deformation in the composites. The deformation of PDMS/MWCNT phase was higher in the PDMS/MWCNT/μ-SiO2 composites than that of the PDMS/MWCNT composites, which leaded to high piezoresistive sensitivity. For example, the gauge factor (GF) of the PDMS/MWCNT composites increased from 1.3 to 62.9 at 30% compression strain by the addition of 30 vol% 1 μm-SiO2 particles. The highest piezoresistive sensitivity was found in the PDMS/MWCNT/μ-SiO2 composites with lowest size of μ-SiO2 particles due to the highest deformation of PDMS/MWCNT phase.