Dispersability of multiwalled carbon nanotubes in polycarbonate- chloroform solutions Ulrike Staudinger * , Beate Krause, Christine Steinbach, Petra P € otschke, Brigitte Voit Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Straße 6, 01069 Dresden, Germany article info Article history: Received 12 May 2014 Received in revised form 30 September 2014 Accepted 5 October 2014 Available online xxx Keywords: Carbon nanotubes Dispersion Polymer solutions abstract The dispersion of commercial multiwalled carbon nanotubes (MWCNTs, Nanocyl™ NC7000) in chloro- form and in polycarbonate (PC)-chloroform solutions was investigated by variation of the polymer concentration, MWCNT amount and sonication time and compared with PC/MWCNT composites, which were processed by melt mixing, subsequently dissolved in chloroform and dispersed via sonication under the same conditions. The sedimentation behaviour was characterised under centrifugal forces using a LUMiSizer ® separation analyser. The space and time resolved extinction profiles as a measure of the stability of the dispersion and the particle size distribution were evaluated. Sonication up to 5 min gradually increases the amount of dispersed particles in the solutions. A significant improvement of the MWCNT dispersion in chloroform was achieved by the addition of PC indicating the mechanism of polymer chain wrapping around the MWCNTs. In dispersions of melt mixed PC/MWCNT composites the dispersion of MWCNTs is significantly enhanced already at a low sonication time of only 0.5 min due to very efficient polymer wrapping during the melt mixing process. However, the best dispersion quality does not lead to the highest electrical conductivity of thin composite films made of these PC/MWCNT dispersions. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction For the development of electrically conductive carbon nanotube (CNT) filled polymer nanocomposites a sufficient dispersion of the CNTs in the polymer matrix is essential. A good quality of disper- sion strongly depends on various parameters like the type of CNT and its geometrical dimensions, the surface properties of CNTs and polymer, the matrix viscosity and the dispersion method, to name but a few. The dispersion of CNTs in thermoplastic polymers via melt mixing and the significant impact of melt mixing parameters like temperature, screw speed or mixing time on the dispersion of CNT and therefore on the electrical properties of the composites have been intensively studied [1e 7]. Further the aspects of polymer viscosity [8,9] and choice of CNT type were discussed by several authors [8,10e13]. To develop thin films of electrically conducting polymer/CNT nanocomposites processing from solution like solu- tion casting, dip coating or spin coating is required. The dispersion of CNTs in organic solvents is supported by sonication, a process which generates cavitation to break the CNT agglomerates, instead of shear forces generated by the mixing elements during melt mixing. Parameters like sonication time, frequency and amplitude significantly influence the degree of CNT dispersion. For many ap- plications surface modification of CNTs is an essential tool to effectively disperse CNTs in solvents and polymers [14]. A number of studies have been published within the last 10 years, characterising the dispersability of CNTs in organic solvents in correlation with their surface properties, considering the solu- bility parameters of nanotubes and solvents. Up to now, these ef- forts have mainly concentrated on dispersions with singlewalled carbon nanotubes (SWCNTs) [15e18]. The dispersion of multiwalled CNTs (MWCNTs) in various organic solvents was dis- cussed by Detriche et al. [19,20]. Few studies focus on the disper- sion of CNTs in polymer solutions [21,22]. Some authors discussed polymer wrapping at CNTs, which was specifically used to improve the dispersion of CNTs in water [23] or organic solvents [24]. Theoretical studies reported the effective wrapping of polymers containing aromatic phenyl rings due to a high binding energy of the polymer resulting in high interfacial adhesion with SWCNTs [25] and postulated a dependency of the interaction strength of the CNT with the polymer on the number of repeating units in the polymer [26]. The group of Szleifer and Yerushalmi-Rozen sug- gested the decoration of SWCNTs with end-tethered polymers as the entropic repulsion among the tethered chains generates a free energy barrier that prevents the SWCNTs from approaching [27,28]. * Corresponding author. Tel.: þ49 351 4658 646; fax: þ49 351 4658 565. E-mail address: staudinger@ipfdd.de (U. Staudinger). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2014.10.012 0032-3861/© 2014 Elsevier Ltd. All rights reserved. Polymer xxx (2014) 1e10 Please cite this article in press as: Staudinger U, et al., Dispersability of multiwalled carbon nanotubes in polycarbonate-chloroform solutions, Polymer (2014), http://dx.doi.org/10.1016/j.polymer.2014.10.012