Effect of scale and surface chemistry on the mechanical properties of carbon nanotubes-based composites

In this article, Multi-Walled Carbon Nanotubes (MWCNTs) of varying diameters, both untreated and polycarboxylated, were dispersed at constant weight percentage in an epoxy matrix, and resulting fracture toughnesses (K _Ic) were measured in each case. We show that changing the MWCNT diameter has two effects on the composite fracture toughness: (i) a small MWCNT diameter enables larger interfacial surface for adhesion maximization, which increases toughness; (ii) at the same time, it limits the available pull-out energy and reduces the MWCNT ability to homogeneously disperse in the matrix due to this same large active surface: this decreases toughness. Most commercially available MWCNTs have a length range of several μm, thus an optimal diameter exists which depends on MWCNT wall thickness and surface treatment. Such optimal diameter maximizes pull-out energy and thus composite fracture toughness. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 Carbon nanotubes (CNTs), when sufficiently dispersed in a polymer matrix, offer exceptional mechanical properties as reinforcement fillers in nanocomposite materials. In addition to homogeneous dispersion, optimization of the interfacial bonding between both contacting phases is essential for CNT incorporation to reach full potential. In this study, multiwalled CNTs of various diameters, both untreated pristine and polycarboxylated, were dispersed at equal weight percentage in an epoxy matrix, and resulting fracture toughnesses have been measured. An optimal diameter exists depending on CNT thickness and surface treatment.