Interface molecular engineering of single-walled carbon nanotube/epoxy composites

Abstract

Dispersion of large single-walled carbon nanotube (SWCNT) bundles into individual nanotubes or small bundles and thus strengthening of the nanotube/matrix interfacial interaction are prerequisites for taking full advantage of the remarkable multifunctional properties of SWCNTs in various carbon nanotube-based composites. Noncovalent functionalization of SWCNTs is an attractive option to simultaneously achieve these conditions. Toward this end, three reactive amino-containing pyrene derivatives (AmPys) with various spacer chain lengths were synthesized. One with the longest spacer length (12 methylene units, AmPy-12) shows the highest functionalization efficiency for SWCNTs in terms of dispersibility. Systematic characterization on a SWCNT/AmPy-12 hybrid suggests that ca. 10 wt% of AmPy-12 is strongly adsorbed on SWCNTs through π–π interactions, making them steadily dispersed into individual ones and/or small bundles without noticeable change in their electronic structure. AmPy-12-functionalized SWCNTs were then used for the preparation of epoxy composites. Since the SWCNT/epoxy interface was well engineered at a molecular level by application of AmPy-12, which interacts noncovalently with SWCNT but bonds chemically to the epoxy matrix, the composite with only 0.3 wt% SWCNTs displays an increase of 54% and 27% in tensile strength and Young's modulus, respectively, over neat resin. A low electrical percolation threshold of 0.1 wt% SWCNTs and improved thermal properties were also observed.