Phenomenological characterization of fabrication of aligned pristine-SWNT and COOH-SWNT nanocomposites via dielectrophoresis under AC electric field

摘要

Dielectrophoresis under the application of AC electric fields is one of the primary fabrication techniques (DEPFT) for obtaining aligned carbon nanotube (CNT)-polymer nanocomposites, and is used here to generate data sets from which DEPFT fabrication models in terms of CNT dispersion and orientation distribution can be developed. While the general understanding of how CNTs form aligned filaments under the influence of dielectrophoretic forces and moments is well established, detailed multi-CNT-filament formation predictions of microstructure evolution from a random dispersion into a more ordered structure remain intractable. As such, effort here is focused towards the development of phenomenological fabrication models for controlling local CNT dispersion and orientation as a function of applied electric field magnitude, frequency, and exposure time. In this study, 0.03 wt% single-wall nanotubes (SWNTs) and acid treated functionalized SWNTs (COOH-SWNTs) were dispersed in a photopolymerizable monomer blend (urethane dimethacrylate (UDMA) and 1,6-hexanediol dimethacrylate (HDDMA)). Ultrasonication techniques were used to obtain the two different acrylate solutions i.e., 0.03% SWNTs/ UDMA/ HDDMA(9/1) solution and a 0.03% COOH-SWNTs/UDMA/HDDMA(9/1) solution, consisting of randomly oriented, well dispersed SWNTs. Pristine SWNTs and acid treated SWNTs solutions were then subjected to controlled AC electric fields in order to explore the formation of aligned SWNT-filaments. To assess key morphological features of the as-produced SWNT-acrylate and SWNT-COOH-acrylate nanocomposite samples, such as SWNT distribution and filament thicknesses, transmission optical microscopy has been used to observe the SWNT alignment and filament formation obtained by digitally mapping individual overlapping images. The acquisition of a large field of view with high magnification allows statistically meaningful distribution functions for morphological features to be constructed. Measurements of the as-produced nanocomposite electrical properties in the SWNT alignment direction and transverse to it were used as a macroscale measure to confirm alignment and contiguity of the SWNT-filament structure, with polarized Raman spectroscopy used to assess the degree of SWNT alignment at the local microscale level. It is observed that a combination of exposure time to AC electric field, and its frequency, is the key driver of filament thickness and spacing and that in general, the COOH-SWNTs align to a greater extent than the pristine SWNTs, though they do not form filaments that are as thick and contiguous for the exposure times studied. POLYM. COMPOS., 36:1266-1279, 2015. (c) 2014 Society of Plastics Engineers