Curing condition influences the piezoresistivity of MWNT/epoxy nanocomposites

Non-monotonic electrical resistance change vs. tensile strain relationships have been observed in MWNT/epoxy nanocomposites, but the mechanism is not fully understood. While previous studies mostly investigated the effect of nanofiller content, this work evaluates the influence of curing condition. The results of electromechanical experiments demonstrate that the monotony of the piezoresistivity of a MWNT/epoxy nanocomposite could be enhanced by employing a higher curing temperature. Moreover, atomic force microscopy and in situ near infrared spectrometry were used to probe the curing kinetics and the curing-dependent molecular structures of epoxy matrices, showing that both rigid domains and compliant domains could develop inside an epoxy matrix during curing and the level of spatial heterogeneity would depend on the curing temperature. Therefore, it is proposed that when cured under a different temperature, an epoxy matrix would exhibit a different level of spatial heterogeneity in molecular structure and hence in mechanical properties, causing the MWNT network inside the matrix to undergo a different movement trend under tension. This work establishes the causal relationship between curing condition and the piezoresistivity of MWNT/epoxy nanocomposites through considering the contribution of the molecular structures of polymer matrices.