Combined Atomic and Molecular Layer Deposition Surface Modification of Carbon Nanotubes for CNT-Epoxy Polymer Composites

Optimizing the interactions between the matrix and reinforcement components is key to attaining high-performance composite materials. Yet, balancing the reinforcing-matrix phase interactions for synthetic composites remains a great challenge. Here, a combined methodology using molecular and atomic layer deposition (M/ALD) is demonstrated for tailoring carbon nanotube (CNT) interfacial interactions, yielding high-performance-reinforced polymer composites. CNT mats are used as a model system to systematically study the molecular details as they do not involve powder processing and other aspects which obscure the understanding of molecular level effects. Noncovalent attachment of the M/ALD layer at the interface allows good wetting of the CNTs, provides an effective means for stress dissipation without compromising the CNTs' Csp2-Csp2 network which remains intact, while introducing amine functionalities to facilitate the cross-linking polymer matrix (epoxy). M/ALD-modified CNT mat-epoxy composites showed an increase in the maximal tensile strength and toughness of up to 32 and 247%, respectively. These findings may pave the way to systematically develop high CNT loading composites as well as other nano-reinforced composite systems showing both high strength and toughness as well as numerous other desirable properties related to nanomaterial composites in general.