Influence of Ni particle size on the piezoresistivity and dielectric properties of Ni/silicone rubber composite

Ni/silicone rubber composites with nickel powders of different particle sizes were prepared at a filler/ silicone rubber mass ratio of 2.4∶1.0. The piezoresistivity and the dielectric properties of the composite samples at room temperature were measured. The mechanism of electric conduction is discussed together with the SEM images of the samples. The results show that piezoresistivity of Ni/silicone rubber composite is enhanced by reducing the filler particle size: at low pressures, the pressure derivative of resistivity, of samples prepared with Ni powders of particle size 74, 48 and 18 μm is 1.73×10⁴、2.59×10⁴ and 3.71×10 ⁴ Ω·m/kPa respectively. The sharp drop in resistivity shifts to the low pressure end as the filler particle size decreases, suggesting that the percolation threshold of Ni/silicone rubber composites decreases with reduced filler particle size. AC conductivity, dielectric constant and dielectric loss of Ni/silicone rubber composites all increase with the decrease of particle size: the conductivity of the sample with filler particle diameter 18 μm reaches about 10^-2 S·m^-1, which is five orders of magnitude greater than that of the sample with filler particle diameter 74 μm(about 10^-7 S·m^-1), and the corresponding dielectric constant is also increased from about 10² to about 10³. Elasticity, piezoresistivity, and electronic transport properties of the composite can be adjusted by changing the filler particle size.