ABSTRACT
Therefore, it is proposed that rubber materials are capable of working as strain sensors.
In a polymer and conductive filler composite, an increase in the filler volume fraction to a certain point Pc, known as percolation threshold (Stauffer and Aharony, 1994), allows the filler particles to gather and form a series of continuous conductive paths which makes the material change from being an insulator to a conductor (Zhang et al., 2012). More interestingly, around Pc a slight change of the filler volume fraction can cause orders of magnitude shift in the conductivity, or permittivity. Actually, the filler particles do not need to have a directly contact with each other to be conductive if the distance between them is as small as a few nanometers, since the electrons can travel through thin polymer layers between the particles by tunneling or hopping mechanisms (Sheng, 1980, Trionfi et al., 2008). There are also theories based on Debye’s relaxation which claim that the average distance between particles can be calculated by dielectric spectroscopy (Ouyang, 2002). Although it has agreed with the results from DC tests and mechanical tests for some composites (Geberth and Klüppel, 2012), more evidence from different filler-polymer systems are needed since the relaxation mechanism for a conductive filler-polymer system is still unclear. At least, it shows that the DS technologies can be a useful tool to study the filler structure.
