HIGH STRAIN SENSORS OF MULTI-WALLED CARBON NANOTUBES AND GRAPHITE FILMS PREPARED ON PRE-STRETCHED NATURAL RUBBER BY DRY SURFACE COATING

Abstract

Conventional metallic strain sensors are flexible, but they can sustain maximum strains of only ~5%. There is a need for sensors that can bear high strains for multifunctional applications. In this study, we report stretchable and flexible high-strain sensors that consist of entangled and randomly distributed multiwall carbon nanotubes or graphite flakes on a natural rubber substrate. Carbon nanotubes/graphite flakes were sandwiched in natural rubber to produce these high-strain sensors. Using field emission scanning electron microscopy, the morphology of the films for both the carbon nanotube and graphite sensors were assessed under different strain conditions (0% and 400% strain). As the strain was increased, the films fractured, resulting in an increase in the electrical resistance of the sensor; this change was reversible. Strains of up to 246% (graphite sensor) and 620% (carbon nanotube sensor) were measured; these values are respectively ~50 and ~120 times greater than those of conventional metallic strain sensors.

Polymer and nanomaterials based piezoresistive sensors have acquired significant attraction because of their multifunctional applications. Though few researchers achieved higher strain limit than the commercial metallic strain sensors, the response curves of those sensors were highly nonlinear. The highest degree of nonlinearity of sensor’s response curves is a serious factor that may limit practical applications. In this present work we report a kind of strain sensors made by coating, multi-walled carbon nanotubes on natural rubber tubes. The relative change in the resistance of the sensors increased linearly with the applied stain. These polymer based multi-walled carbon nanotubes sensors showed greater linear response as well as higher strain limit (720%). By adding graphite flakes to the multi-walled carbon nanotubes the sensitivity of the sensors was varied. The effect of the CNT-graphite weight ratio on sensor’s sensitivity and strain limit was also investigated.