Effect of swelling on the electrical behavior of nitrile/graphite rubber composite and break down of graphite network

Research subject:

 The sensitivity of electrical conductivity of rubber/conductive filler composites against swelling strains is a phenomenon that can lead to the creation of sensors to detect the type or leakage of hydrocarbon liquids. In the swollen conductive composites, the variation of filler network structure reduces the Statistical frequency of the tunneling and interconnection of conductive particles. This behavior can be a sign for a solvent or hydrocarbon fuel detector system in a flexible sensors.

Research approach:

 In this study, nitrile rubber/graphite composite samples with several concentrations (20, 30, 40, 50, 60, 70 and 80phr) of graphite particles were prepared and their electrical characteristics were measured. The changes in the electrical resistance of nitrile rubber /graphite samples were investigated based on increasing the content of graphite particles, immerse to toluene, and repeating the period of the swelling/recovery process for each sample.

The sensitivity of composites with higher concentrations than the percolation threshold (53.5phr of graphite particles) to the conductivity changes due to the swelling phenomenon is appropriate for use in the sensor. Also, incremental changes in the electrical resistance of the samples immersed in the toluene solvent were measured and it was observed that all the samples were eventually converted to electrical insulation. In order to study the repeatability performance of sensor, samples with 60, 70 and 80phr of filler were swelled and recovered for three periods, which is less than the conductivity of the sample before the second and third swelling process compared to the conductivity before the first one. This difference is very small in the sample containing 80phr of graphite particles. The trend of change in electrical resistance is significantly different in the second swelling process compared to the primary swelling. But there is little difference between the third swelling process and the second one. This phenomenon has occurred for all three samples, which can be observed to be similar to Mullins effect.