Nanotube Alignment Using Lyotropic Liquid Crystals

Carbon Nanotubes in Liquid Crystals

“…In our initial work we used SDS for dispersing HiPco SWCNTs as well as for forming the LC phase 25,26 , the latter 55 being a nematic phase forming at 25 wt.-% surfactant concentration if some 5 wt.-% of decanol is added as cosurfactant 56 . By tuning the exact composition of the final mixture we could select to have disc-shaped 25 or rod-shaped 26 micelles forming the nematic phase.…”

“…However, many synthesis methods are ruled out by the requirement to use a substrate and, more important, the lack of chirality control and possibility to 20 efficiently purify the product means that the tubes will have random electronic properties and be surrounded by impurities such as catalyst rests and amorphous carbon particles. Two different protocols for post-growth CNT fractionation according to chirality and diameter have recently been 25 described 12,13 , but these require, just like most purification methods, non-supported nanotubes, free from any substrate. Finally, the aligned-growth methods are far from trivial and scale-up is challenging.…”

“…Although clearly an appealing concept, we will in this review only briefly touch upon this issue, as the observations are far from understood and have also been challenged by contradictory reports 22,23 . In contrast, the CNT-in-LC alignment concept is by now well established with 70 experimental studies by us and other groups clearly having demonstrated its potential [24][25][26][27][28][29][30][31] . Nevertheless, a number of important challenges still remain to be addressed before it can reach large-scale industrial usage.…”

“…Obviously, this requirement is very well fulfilled by typical thermotropic mesogens, hence we can expect aromatic interactions to contribute to successful CNT dispersion in thermotropic LCs. Indeed, a quantitative Raman study by 25 Scalia et al 43 clearly showed that the aromatic and polar 5CB molecule interacts strongly with SWCNTs, as detected through a shift in the main peak of the CNT G-band (see below for a discussion of the CNT Raman response). Very few studies 43,44 have so far dealt specifically with the 30 questions related to CNT dispersion in thermotropic nematics, hence this is a topic open for future investigative efforts, theoretical contributions being particularly needed.…”

“…While this depletion attraction limits the amount of CNTs that can be suspended, as well as the 70 maximum concentration of surfactant, its exact role in liquid crystalline systems is somewhat unclear, as all modelling of depletion phenomena that we know of has been done for the case of spherical micelles forming an isotropic phase. The fact that lyotropic LC phases have been successfully loaded with 75 CNTs [24][25][26]51 at a surfactant content well beyond the limit where an isotropic aqueous CNT-surfactant system was reported to suffer strongly from depletion attraction 49 suggests that the special conditions of the LC phase has considerable impact on the phenomenon. In particular, one 80 must probably take the impact of long-range orientational order of elongated micelles (both with and without nanotubes) on the total excluded volume into account.…”