Particle Size Effect Of The Nickel/Silicone Rubber Conductive Composites

Ni-silicone rubber conductive polymer composites were prepared with the silicone rubber (110) as matrix and Nickel power of different particle size as filler. The morphology and structure of Ni-silicone rubber conductive polymer composites is discussed together with the SEM image of the samples. First, experiments were carried out on the sample's piezoresistive effect, the percolation threshold and dielectric properties. Then, the magnetoelectric effect of Ni-silicone rubber polymer composites with Ni powders of particle size 74μm was discussed,and MR of Nickel-silicone rubber polymer composites with nickel powders of different particle size was researched .The results show that:(1) Under the same conditions, piezoresistivity of nickel-silicone rubber composite (filler particle size at micron level) is enhanced by reducing the filler particle size. The resistivity of Ni/silicone rubber composite decreases with filler particle size down to 3μm. However, abnormal increase in resistivity occurs when filler particle size is reduced to 300nm; it is even larger than that for the maximum particle size (74μm) of 1 # sample. This shows that piezoresistivity of Ni/silicone rubber has a turning point between the 3μm ~300nm.(2) When the filler particle size is at the micron level, the percolation threshold of the composite decreases as the filler particle size decreases. The percolation threshold of the composite of filler particle size 74 and 3μm was 3.0:1 and 2.6:1 respectively.(3) At a fixed pressure, the ac conductivity of the composite increases with time and reaches a saturation sate after 22 minutes. When the filler is at the micron level, ac conductivity, dielectric constant and dielectric loss of Nickel-silicone rubber polymer composites all increase as the filler particle size is decreased. But the conductivity versus frequency curve for the sample with filler particle size 300nm appears below all the curves for samples with different filler particle size, indicating that there is a turning point between the 3μm and 300nm..(4) A magnetic hysteresis loop was observed in a Ni /silicone rubber composite with Ni powders of particle size 74μm (filler-polymer ratio of 2.7:1 by weigh), showing that the Ni / silicone rubber composite is ferromagnetic. The resistance of Ni/silicone rubber composite decreases with increasing magnetic field below 1500Gs. Above 1500Gs,the magnetization reaches saturation and the resistance increases with increasing magnetic field. When the magnetic field decreases from 5000Gs to the 0Gs, the resistance decreases rapidly down to a magnetic field of 1000Gs below which resistance increases slightly.(5) Without pressure, the MR of Ni / silicone rubber composites with filled powders of different particle size is divided into two regions: the magnetic resistance increases as the filler particle size decreases when the magnetic field is less than 1500Gs and the magnetic resistance decreases with decreasing particle size when the magnetic field is more than 1500Gs .This study shows that Ni /silicone rubber composite exhibits the best piezoresistive effect, the maximum conductivity and dielectric constant when the particle size of Ni powders equals 3μm. Moreover, the dependence of the resistivity on the magnetic field of Ni /silicone rubber composite with filler particle size 74μm is investigated in detail. Finally, the dependence of the MR of Ni / silicone rubber composites on various filler particle size has been studied. The results obtained in the present paper can be very interesting and useful for the application of the Ni /silicone rubber composite.