To describe accurately the electronic structures of carbon nanotubes, a semi-empirical tight-binding approach is presented in which the main intrinsic curvatures have been fully taken into account. The calculated electronic structures and band gaps are consistent with experimental measurements. Studies of the relative importance of various intrinsic curvatures show that each curvature has a contribution of varying importance to the curvature-induced band gap. Additionally, under both uniaxial and torsional strain, semiconductor–metal–semiconductor phase transitions have been observed for primary metallic carbon nanotubes. The critical stress of the transition and the gap’s sensitivity with stress are dependent on both the diameter and chirality of nanotubes, which is at variance with previous predictions.

No abstract

Porous carbon nanotube (CNT) buckypapers (BPs) with various porosities were obtained by using a positive pressure filtration method. The porosity of the BPs fell into a wide range of 11.3–39.3%. Electrical conductivities and tensile mechanical properties of the prepared BPs were then measured and correlated with the porosity of the CNT BPs. Results demonstrated that the conductivities, tensile strength, and elastic modulus of the BPs could decrease by increasing their porosity. The elongation at break of the BPs on the other hand did increase significantly, suggesting improved toughness of the BPs. The obtained electrical conductivity and tensile strength of the porous BPs can reach nearly 0.6 S/m and 26 MPa, respectively, which may be potentially useful in composites reinforcement and conductive materials.

In the present study, a positive-pressure filtration method was proposed to prepare carbon nanotube buckypapers (CNT BPs) with desirable porosity and mechanical properties. The obtained BPs were then infiltrated with epoxy via vacuum-aided resin transfer molding (VARTM) process without the use of a solvent. Some of the impregnated composites were directly cured under a vacuum pressure. The others were put into a hot-press to cure under a higher pressure of 0.7 MPa. Results have shown that the tensile strength and modulus of the vacuum cured composites were obtained as 215 MPa and 13.3 GPa, whereas these two values could reach 319 MPa and 20.3 GPa, respectively, for the hot-press cured composites. The glass transition temperature of the hot-press cured composites was also improved by 7% compared with that of the vacuum cured composites. Furthermore, SEM observation revealed that the BPs were infiltrated well with epoxy and good interfacial bonding between CNTs and epoxy was obtained. This study has demonstrated that the random aligned CNT BPs reinforced epoxy composites possessing desirable mechanical properties can be fabricated by using conventional processes when the microstructure of the BPs is improved. POLYM. COMPOS., 00:000-000, 2016.

No abstract