Tribological Anisotropy Of Oriented Carbon Nanotubes / Polymer Composites

Carbon nanotubes (CNTs) represent one of the most studied nanostructures in recent years. Due to their extraordinary mechanical, optical, electrical, magnetic, and thermal properties, CNTs have been proposed for a broad spectrum of applications in the fields of structural material, energy storage, biology, medicine and photovoltaics. On the other hand, due to their low cost, easy fabrication, and tunable structures, polymers have been widely studied and used for friction materials. Nevertheless, the use of polymers in tribological applications has been limited by low mechanical strength and wear resistance. To further improve the tribological property, a second phase was usually introduced to produce composite materials with incorporated new properties. Among them, CNT has been widely studied as one of ideal candidates. However, there remains a common and critical challenge, i.e., random dispersion and aggregation of CNTs in polymer matrices. The resulting composite materials have not fully taken advantage of the excellent properties of individual CNTs. This thesis focuses on the preparation of high performance CNT/polymer composites in which CNTs are highly aligned in the polymer matrices.Firstly, CNT arrays were synthesized via chemical vapor deposition method; then, highly aligned CNT films were prepared by dry spinning or pressing method; finally, aligned CNT/poly(methyl methacrylate) and CNT/polystyrene composites were produced by spin-coating and in-situ polymerization, respectively. In these composites, the side walls of CNTs were partially exposed on the composite surface while the others were imbedded in the polymer matrices. Friction force microscopy and M-2000friction and wear tester were used to study their tribological properties at microsized and macroscopic scales, respectively.Three main conclusions are summarized as below:(1) For the aligned CNT/PMMA composite film, the friction coefficient in the transverse direction was about2times of that in the longitudinal direction relative to the CNT axis;(2) For the aligned CNT/PS composite material, the wear rate in the transverse direction was nearly3times of that in the longitudinal direction relative to the CNT-aligned direction; (3) The addition of CNTs had greatly increased mechanical strengths, wear rates, electrical conductivities and thermal stabilities of the composite materials.