Multidirectional Hierarchical Nanocomposites Made by Carbon Nanotube Growth within Layer-by-Layer-Assembled Films

We demonstrate fabrication of multidirectional and hierarchical carbon nanotube (CNT) films on diverse substrates, using nanocomposite catalyst films prepared by layer-by-layer (LBL) assembly. CNT density and yield are controlled by the thickness of a montmorillonite clay/poly(dyallyldimethyl ammonium chloride (MTM/PDDA) support film. Using identical methods, few-walled CNTs are grown on flat silicon substrates, carbon fibers, and titanium wire mesh. On flat substrates, unique bilayer CNT forests, reminiscent of microscale accordions, form because of diffusion of the Fe catalyst through the support which is then split because of mechanical forces exerted by the growing CNTs. Electrochemical measurements of CNT-coated Ti wires demonstrate an 85-fold enhancement in specific capacitance, and 7.1 F/g for the CNTs alone. This novel approach to substrate engineering for CNT growth can create materials with unique and nonlinear properties by hierarchical ordering of CNTs at multiple length scales, and is scalable to large-area foils and fabrics.