Quantitative Analysis of Positive Temperature Coefficient Characteristics of Conductive Composites

Conductive polymer composites filled with carbon or metal particles exhibit a positive-temperature-coefficient (PTC) of resistivity. In our previous studies, we speculated that only the volume expansion of polymers upon heating cause the PTC effect and we conducted quantitative analyses focusing on the decrease of the apparent filler content of the composites during volume expansion of polymers. Later, we found that PTC effect occurs when the conductive path is cut off due to crystal melting and volume expansion of the base polymer along with rising temperature. In this study, we analyzed the PTC effect of polyvinylidene fluoride (PVDF)/Ni composite quantitatively and found that the apparent Ni content (C-Ni(T)) decreases along with rising temperature. When C-Ni(T) becomes about 98% of the Ni content at room temperature (CNi-R.T.), the resistivity is 10 times of that at room temperature. When C-Ni(T) becomes about 96% of CNi-R.T, the resistivity exceeds 10(8) Omega.cm and the composites serve as insulators. In conclusion, we proved that, the Ni content is not constant when the PTC effect occurs.