Carbon nanotube (CNT) polymer nanocomposites are promising new materials with a unique combination of mechanical and transport properties. As physical properties such as mechanical behavior, dielectric relaxation, thermal and electrical conductivities depend strongly on morphological structures of composites, we illustrate, in this study, the structure/property relationship in CNT/polymer nanocomposites with both randomly oriented and vertically aligned carbon nanotubes.

Composites of randomly oriented multiwalled carbon nanotubes (MWNT) and polyimide (PI) were synthesized via in situ polymerization. The tensile strength of MWNT/PI with 15wt. % and 20wt. % of entangled CNTs was measured. The fracture surfaces were examined using field emission scanning electron microscopy (FESEM). Another approach involves using pre-shaped MWNT networks as reinforce materials. Entangled MWNT networks were grown inside small quartz tubes to fill the entire space; styrene monomers were injected under vacuum and polymerized within the tubes without disrupting the as-grown MWNT networks. Thus synthesized composites are compared to those prepared via solution procession.

In another experiment, vertically aligned CNT (VACNT)/polymer nanocomposites were prepared via both solution processing and in situ polymerization. Three polymers [poly(methyl methacrylate), polystyrene and polyimide] were used in solution preparation of composites, in which polymers infiltrate into the vacant space among the VACNTs. For in situ polymerization, VACNT slabs were geometrically confined inside rectangular glass tubes followed by monomer (styrene) injection under vacuum and polymerization. Transport properties and mechanical properties from nanoindentation tests were discussed in the light of the composite morphology as revealed by FESEM and small angle neutron scattering.