Generally, the number of contacts increases with an increase in the number of filler particles of large aspect ratio, so the contact resistance predominates. In this case,
the filler particles link one another to form a conducting network throughout the system, leading to high conductivity of the composite. As recognized, molecular chain movement is activated when the temperature exceeds glass transition temperature of the polymer. For the AgNW/TRG/PVDF composite, TRGs can make many contacts with the polymer matrix because of their large surface-to-volume ratio. Thus, low-density TRGs sense quickly to the movement of polymer molecular chains as the temperature increases. In contrast, AgNWs with higher density respond slowly to molecular chain movement. U0126 An increase in temperature can disrupt conductive path network by increasing the distance between TRG fillers as shown in Figure 6a,b. The separation of AgNWs and TRGs due 3 Methyladenine to heating causes a reduction in the overall contacts among AgNWs and TRGs, resulting in a gradual increase in resistivity.
PTC materials generally find useful applications for fabricating temperature sensors and self-regulating or current limiting devices [47, 48]. The pronounced PTC behavior of the AgNW/TRG/PVDF composites enables the materials to respond very rapidly to the changes in temperature. Thus, the hybrids are novel PTC materials finding attractive usage in industrial sectors for a variety of smart and functional applications. Figure 6 Schematic Ponatinib ic50 diagrams showing the dispersion of TRGs and AgNWs in a hybrid (a) before and (b) after heating. Conclusions AgNW/TRG/PVDF hybrid composites were prepared using solution mixing followed by coagulation and thermal hot pressing. Electrical measurements
showed that the bulk conductivity of hybrids was higher than a combined total conductivity of both TRG/PVDF and AgNW/PVDF composites at the same filler loading. This was due to the AgNWs bridged TRG sheets effectively in forming a conductive network in the PVDF matrix, producing a synergistic effect in conductivity. Consequently, electrical conductivity of 2 vol % AgNW/0.08 vol % TRG/PVDF composite was comparable to measured conductivity of graphite paper. Finally, the resistivity of hybrid composites increased with increasing temperature, particularly at the melting temperature of PVDF, generating a pronounced PTC effect. This effect was caused by the volume expansion of PVDF matrix with increasing temperature, which disrupted the synergistic effect and reduced electrical contacts among the conductive fillers. Acknowledgements This work is supported by the project (R-IND4401), Shenzhen Research Institute, City University of Hong Kong. References 1. Meng YZ, Hay AS, Jian XG, Tjong SC: Synthesis and properties of poly(aryl ether sulfone)s containing the phthalazinone moiety. J Appl Polym Sci 1998, 68:137–143. 10.1002/(SICI)1097-4628(19980404)68:1<137::AID-APP15>3.0.