Geometry-Induced Mechanical Properties of Carbon Nanotube Foams

Carbon nanotube (CNT) foams have unmatched energy absorption properties derived from their complex hierarchical structure. The control of the micro-scale geometry of these foams allows tuning their behavior to specific application-driven needs. Geometrical structures in CNT foams are obtained by synthesizing CNTs on substrates patterned with different growth templates: circles, lines and concentric rings. To study the effects of the microstructural geometry on the bulk mechanical response of the foams, the samples are tested under cyclic quasi-static compressive deformation (up to 50% strain). The geometry of the patterns plays a fundamental role on the samples' macroscopic energy absorption capability, maximum stress, and strain recovery. Patterned CNT structures demonstrated mechanical properties comparable or improved over non-patterned, bulk CNT foams, but with much lower density. Quasi-static compressive tests performed on different patterned structures with the same effective density (ρ = 0.02 g cm−3) exhibit considerably different responses. For example, the stress reached by foams patterned in concentric rings is ≈15 times higher than that observed for pillars and lines. The results show how the mechanical response of CNT foams can be tailored by varying the CNT microstructural architecture.