Negative temperature coefficient and positive temperature coefficient behavior of electrically conductive silicone/carbon black composites

As highlighted in several studies, the thermal expansion of the polymer matrix plays an important role with respect to the thermo-electrical behavior of conductive composites. Although it is known that the crosslink density of polymers affects the thermal expansion of polymers, no studies are known on whether different crosslink densities can affect the thermoelectric behavior of electrically conductive composites. In this study, silicone/carbon black composites with different crosslink densities, were investigated with respect to their self-heating properties under applied voltages and their thermo-electrical behaviors like positive and negative temperature coefficients. Specific resistances rho about 55 +/- 4.5 omega-cm have been achieved and uniquely high negative temperature as well as low temperature coefficients were demonstrated, which make these materials interesting for sensor-technical applications. Regarding their self-heating behaviors, average surface temperatures of up to 147 degrees C were measured, which further make these materials very interesting as flexible heating elements. Finally, it could be shown that the crosslink density of addition curing silicones is adjustable over a wide range and that it can be further significantly changed by the addition of carbon black and platinum content.