At present, conductive rubber products as functional rubber products have developed rapidly and are widely used. This paper mainly introduces the conductive mechanism of rubber, the factors affecting the conductive properties of rubber, and the varieties and applications of conductive rubber.
Conductive rubber is a composite conductive polymer material. Its conductive mechanism mainly includes macro seepage theory (conductive path mechanism), micro quantum mechanical tunnel effect and micro quantum mechanical field emission effect.
(1) Conductive path mechanism when the amount of conductive filler in rubber increases to a certain critical value, a more complete conductive path network is formed in rubber, and the resistivity of rubber will decrease sharply. In the relationship between resistivity and the amount of conductive filler, there is a narrow abrupt region. Any small change in the amount of conductive filler in this region will lead to a significant change in rubber resistivity. This phenomenon is called percolation phenomenon, and the critical amount of conductive filler is usually called percolation value.
(2) Tunnel effect when the amount of conductive filler is small, the spacing of conductive particles in the rubber matrix is large, and the conductive path network has not been formed in the microstructure of the composite. At this time, there may still be conductive phenomenon. This conductive phenomenon is caused by the migration of thermally vibrating electrons between conductive particles, and the conductive current is an exponential function of the gap width of conductive particles. Tunnel effect almost only occurs between conductive particles with close distance, and there is no current conduction between conductive particles with too large gap.
(3) Field emission effect
When the amount of conductive filler is small and the spacing between conductive particles in the rubber matrix is large, if the internal electric field of conductive particles is very strong, electrons will have a great chance to leap over the polymer interface barrier and transition to adjacent conductive particles to generate field emission current and form a conductive network.
Conductive path mechanism, tunneling effect and field emission effect exist simultaneously in conductive rubber, which may be dominated by one or two mechanisms under different conditions. When the amount of conductive filler is above the critical amount, the conductive path is the main conduction mode, that is, the conductive path mechanism is the main mechanism; When the amount of conductive filler is small or the applied voltage is small, the gap of isolated electrons or their aggregates is large and can not participate in conduction, the thermally excited electrons transition and form a large tunnel current, which is dominated by tunnel effect; When the amount of filler is small and the internal electric field between particles is strong, the matrix spacer is equivalent to the internal distributed capacitance, and the field emission effect is more significant.