Negative liquid sensing effect and tunable piezoresistive sensitivity in polydimethylsiloxane/carbon nanotubes/water-absorbing-expansion particles nanocomposites

Herein, a negative liquid sensing effect and tunable piezoresistive sensitivity was achieved in polydimethylsiloxane/multi-walled carbon nanotubes (PDMS/MWCNT) composites with water-absorbing-expansion (WAE) particles. The conductivity of the PDMS/MWCNT composites without WAE particles decreased in water, showing a typically positive liquid sensing effect. In the PDMS/MWCNT/WAE composites, the WAE particles expanded in water to several times in their volume, which compressed the PDMS/MWCNT domains and increased conductive paths. The absorption of water also enhanced the conductivity of WAE particles. As a result, the conductivity of the composites increased in water, showing an unusually negative liquid sensing effect. Furthermore, the PDMS/MWCNT/WAE composites, which showed more sensitive to water, had stable conductivity after being taken away from water at room temperature but could be recoverable at high temperature. In addition, the piezoresistive sensitivity of the samples could be tuned by the expansion ratio of WAE particles via controlling the immersing time in water.