Surfactant-CNT dispersions

In practice, although it is seldom clearly stated, all parameters [such as glass ware type, surfactant-CNT dispersion volume, position of the sonicator tip in the sample or sample location in a bath sonicator, etc.] need to be kept fixed for optimum control and reproducibilityofdebundlingexperiments [providedthecomposition of the CNT batch used remains homogeneous]. Additionally, Mason and Lorlmer calculated that any experiment should be carried out at the lowest possible temperature in order to get maximum sonochemlcal benefit. Controlling the temperature is crucial since the surfactant-CNT dispersion heats up during the sonication, which... 

With the simple and efficient UV-Vis tool to monitor the sonication-driven debundling of SWCNTs and MWCNTs, the optimum debundling conditions can be determined to produce stable surfactant-CNT dispersions that can be further stored and employed to make conductive nanocomposites. Finding trends in the general debundling behavior of several types of CNTs, as well as selecting the right power of sonication and the optimum CNT and surfactant concentrations, are dealt with in this section. 

For the production of nanocomposites with the latex-based concept, it is preferable to be able to work at (relatively] high concentrations of exfoliated CNTs for reproducibility purposes (in order, for example, to be able to prepare a full series of nanocomposites of different CNT loadings by diluting the same surfactant-CNT dispersion], as well as for commercial reasons. 

At the end of the debundling process, aqueous surfactant-CNT dispersions not only contain dispersed and mostly exfoliated CNTs, covered by surfactant molecules and detectable by UV-Vis spectroscopy. Also present are carboneous impurities such as graphene nanoparticles or amorphous carbon, catalyst particles, and possibly some bundles of CNTs that were not exfoliated. 

Issue Concerning the Calculation of CNT Concentration in Aqueous Surfactant-CNT Dispersions... 

Centrifugation leads to the preferential removal of the densest constituents of the multi-component systems constituted by aqueous surfactant-CNT dispersions. The nature and the quantity of species removed are strongly related to the CNT type and batch [as already illustrated in the previous paragraph] and to the surfactant types. Regarding this last point, it has been foreseen and/or demonstrated many times that all surfactants do not necessary have the same ability to exfoliate CNTs [see refs. 13, 14, 189, among others]. In particular. Tan and Resasco developed a method based on UV-Vis spectroscopy for quantifying the [individual CNT]/[CNT bundle] ratio. This method leads to the ranking of the relative ability of surfactants to exfoliate SWCNTs. 

Regarding the SWCNTs sorting quest, it is important to stress the advantage of using UV-Vis[-NIR] and, more generally, absorption spectroscopy for analyzing the detailed composition of surfactant-CNT dispersions [in terms of bundle, diameter and/or electronic structure distribution] over the other possible method, namely, Raman spectroscopy. Both techniques were proven to be very... 

UV-Vis-NIR spectroscopy can be further optimized and refined to assert and compare the efficiency of purification techniques. This will also help calculate the true CNT concentration and the exact composition, in terms of diameter and electronic structures [the latter being tuned by a careful choice of surfactant and experimental conditions] of the supernatant of centrifuged surfactant-CNT dispersions. 

To sum up, UV-Vis spectroscopy appears to be a crucial and readily accessible tool for the characterization of surfactant-CNT dispersions, in terms of composition and optimization of preparation parameters, which can be further used to produce technologically interesting CNT/polymer nanocomposites, as will be shown in the following chapters of this book. 

Here, an alternative approach based on masterbatches is presented in order to prepare CNT/PPO/PS nanocomposites. Instead of directly mixing a surfactant-CNT dispersion with a PPO/ PS polymer in the form of a latex, the nanocomposite was prepared in two steps. The first step consisted of producing a MWCNT/ PS masterbatch with a relatively high, well-dispersed MWCNT... 

---