Effect of graphene nanoplatelets thickness on strain sensitivity of nanocomposites: A deeper theoretical to experimental analysis

Abstract

Conductive epoxy nanocomposites were prepared using two different thickness graphene nanoplatelets (GNPs) as reinforcement, H25 and M25. In both cases, 3 and 5 wt % GNPs was dispersed into the matrix by means of sonication and calandering processes. The piezoresistive mechanisms of these GNPs/epoxy sensors were studied under tensile and flexural tests. Under tensile loads, H25 nanocomposites, with 15 nm thickness, have a lower sensitivity at low strains and higher at high strains than M25 ones, with 6 nm thickness. This apparently anomalous behavior is explained under the basis of a theoretical model where two types of contacts between GNPs are considered. H25 nanocomposites show a prevalence of type I tunneling mechanisms at low strains and a prevalence of type II contacts at high strains, explaining this more pronounced exponential effect of the electrical resistance. In case of flexural tests, tensile and compressive subjected faces were monitored separately. Lower values of sensitivity than in tensile tests were observed due to the influence of breakage and creation of electrical pathways, showing a similar trend at low and high strains for H25 and M25 nanocomposites.