Model on the thermal-switch property of conductive particle filled polymers

The volume fraction of conductive particles is a switch from insulator to conductor in the polymeric positive temperature coefficient (PTC) of resistance composite. The thermal volume expansion is a leading factor of the PTC effect. The theoretical model and experimental results prove that the conductive mechanism of abrupt resistivity increase at PTC transition range is equivalent to that at the percolation curve close to the critical volume fraction. PTC transition temperature and temperature-coefficient were influenced by the conductive particle loading level, if the composite has percolate conductive character. The PTC materials can be designed by controlling the volume fraction of conductive particles.