Strategic approaches for dispersing and/or orienting SWNT in films and composites are essential for controling and optimizing their properties [1,2]. Dispersion in a liquid phase is the most efficient way to exfoliate the bundles into individual SWNT. Additives, most often surfactants, have to be used because of the poor solubility of SWNT in all solvents. However, the presence of surfactants in the final films/composites can drastically change their properties. In this talk, we show that a simple dialysis process opens a new route for stabilizing aqueous inks with high concentrations of individual SWNT without surfactant, and for preparing surfactant-free polymer-based composites [3]. Coupled Raman/ photoluminescence spectroscopy studies allow to probe in situ both the dispersion of the nanotubes and the nature of the molecules adsorbed on their surface. We demonstrate a spontaneous exchange between surfactant molecules (bile salts) and polyvinyl alcohol (PVA) chains at the surface of the nanotubes, and a forced exchange by dialysis for both PVA and polyvinyl pyrrolidone (PVP) [3].
On the other hand, we study the processing of SWNT aqueous inks into patterned deposits by inkjet printing. We show that a good control of both the morphology of inkjet printing lines and of the alignment of SWNT in these lines can be achieved by tuning the SWNT concentration, inter-drop distance and substrate temperature. Using polarized micro-Raman spectroscopy, we present an original method to determine the spatial distribution of nanotubes in the deposits as well as their orientation. We show that two types of line morphologies can be obtained: homogeneous deposits or pairs of ‘‘railway tracks’’. Highly oriented SWNT patterns can be observed in the “railways tracks” and at the edge of the homogeneous lines.
References:
[1] Ph. Avouris. Acc. Chem. Res. (2002) 35, 1026
[2] P. M Ajayan et al, Nature. (2007) 447, 1066
[3] F. Torres-Canas et al, J. Phys. Chem. C 119, 703 (2015)
[4] F. Torres-Canas et al, in preparation