Contacts transition induced stiffening mechanism in CNT-network/epoxy composites

Abstract

The origin of abnormal enhancement in the elastic modulus of CNT-network/polymer composites is a fundamental but unresolved issue. Through mesoscale molecular dynamics simulations, we revealed that contrary to the conventional beliefs, it is not the improved interface load transfer ability among well contacted bundles but a contacts transition induced stiffening mechanism among weak contacted bundles that triggers such an abnormal enhancement. This is because the presence of epoxy molecules into the network pores leads to a remarkable densification effect on the composites thickness, improving the strength of those weak contact junctions between neighboring CNT layers and turning them into load-bearing contact junctions. Such a contacts transition phenomenon significantly increases the number of contact nodes and therefore load transfer paths within CNT-network, enabling more than one order of magnitude improvement in the composite modulus. Specifically, the proposed stiffening mechanism is correlated to the content of introduced epoxy, offering an effective route for tailoring the mechanical properties of derived composites.