Tuning the piezoresistive strain‐sensing behavior of poly(vinylidene fluoride)–CNT composites: The role of polymer–CNT interface and composite processing technique

Abstract

AbstractIn order to understand the role of polymer–carbon nanotube (CNT) interface and composite processing method on strain‐sensing properties, poly(vinylidene fluoride) (PVDF)‐CNT composites have been prepared by melt‐mixing and solution‐casting methods using pristine and acid‐treated CNTs with CNT content of 0.15–4 wt%. The strain rate applied was in the order of s−1. Besides the improved mechanical properties of the composites over pristine PVDF, the piezoresistivity was also profoundly affected by the gentle acid‐treatment of CNTs and the composite processing method leading to tunable strain‐sensing properties. The stability of the strain‐sensors has been further predicted by employing cyclic piezoresistive tests. Interestingly, the pristine CNT composites showed higher strain‐sensitivity likely due to weak interface with polymer and higher initial resistance than the acid‐treated counterparts; while the acid‐treated CNT composites showed better retention of sensing properties under repeated cycles. On the other hand, composites with larger CNT length showed higher strain‐sensitivity than that having shorter CNTs. The temperature dependence of strain‐sensitivity showed a transition from positive to negative temperature coefficient at ~90°C. Finally, the composites subjected to a large number of bending cycles showed excellent performance and stability of strain‐sensing properties, paving the way for development of robust strain‐sensors for structural health monitoring.