| Conduction behavior for carbon black (CB) filled poly(methyl vinyl siloxane) (PMVS) conductive composites was studied. Resistivity (Conductivity) dependences on the ambient temperature, uniaxial pressure and time were investigated. The effects of the filler volume fracition and crosslinking degree were also considered.The relationship of resistivity and the filler weitht fraction for conductive composites based on PMVS was analysed. The composites showed typical percolation characteristic. The conduction behavior in PMVS/CB crosslinked composites followed the prediction of statistical percolation theory.Conduction behaviors of PMVS conductive composites undergoing thermal cycles or subject to thermal treatment at given temperatures were investigated. At CB weight fractions φ slightly above the percolation threshold φc, the resistivity-temperature properties exhibited a weak negative temperature coefficient (NTC) effect and a weak positive temperature coefficient (PTC) effect, respectively. The transition temperature was 110℃. At φ>>φ_c. only the NTC effect was observed. The NTC effect corresponded to thermal activation conduction mechanism, while the PTC effect was related to the breakdown of conductive network caused by volume expansion. The resistivity-temperature curves were not consistent with each other during heating and cooling. The resistivity-temperature curves during thermal cycles were gradually changed towards low-resistance. At given temperatures, resistance exhibited relaxation behavior, which was strengthened with decreasing CB weight fraction and increasing ambient temperature.Resistance of PMVS conductive composites strongly depended on uniaxial pressure, showing piezoresistivity behavior. At φ slightly above φ_c, resistance first increased with pressure and then turned to decrease at a critical pressure, exhibiting a positive pressure coefficient of resistance (PPCR) and a negative pressure coefficient of resistance (NPCR) effects, respectively. Resistance firstly increased with decreasing stress during unloading, showing a weak NPCR effect, and then turned to astrong PPCR effect. NPCR effect became much more pronounced at φ>>φ_c while compressive cycles facilitated the occurrence of the weak PPCR effect during loading. The composites exhibited strong NPCR effects during unloading and the PPCR effect could not be observed. Resistance after completely unloading decreased nonlinearly with time, showing a typical resistance relaxation. The true stress at the PPCR-NPCR transition was related to the structure of the CB concentration and the percolation network before loading. There existed an essential relationship between the structure of the percolation network at the PPCR-NPCR transition of a loading and that before loading.Resistance decreased with time under constant stress and after completely unloading, exhibiting a typical resistance relaxation. Under 2-4 MPa stress, relaxation process was characterized two relaxation times independent of the content of CB, corresponding to the structure change of conductive network on two different scales. After unloaded completely, matrix recovery resulted in the occurrence of structure relaxation, and the relaxation times increased with CB content.Increasing the amount of crosslinking agent could weaken the NPCR effect at the end of compression and enhance the piezoresistivity intensity at a high stresses. The recover}' property of resistance was related to CB content, the stress level and the degree of crosslinking. It was proved that repeated compression with the same maximum stress level could improve the piezoresistive stability considerably.
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