Molecular mechanisms of salt effects on carbon nanotube dispersions in an organic solvent (N-methyl-2-pyrrolidone)

Abstract

We consider the effects of salt (sodium iodide) on pristine carbon nanotube (CNT) dispersions in an organic solvent, N-methyl-2-pyrrolidone (NMP). We investigate the molecular-scale mechanisms of ion interactions with the nanotube surface and we show how the microscopic ion-surface interactions affect the stability of CNT dispersions in NMP. In our study we use a combination of fully atomistic Molecular Dynamics simulations of sodium and iodide ions at the CNT-NMP interface with direct experiments on the CNT dispersions. In the experiments we analyze the effects of salt on the stability of the dispersions by photoluminescence (PL) and optical absorption spectroscopy of the samples as well as by visual inspection. By fully atomistic Molecular Dynamics simulations we investigate the molecular-scale mechanisms of sodium and iodide ion interactions with the nanotube surface. Our simulations reveal that both ions are depleted from the CNT surface in the CNT-NMP dispersions mainly due to the two reasons: (1) there is a high energy penalty for the ion partial desolvation at the CNT surface; (2) NMP molecules form a dense solvation layer at the CNT surface that prevents ions to come close to the CNT surface. As a result, an increase of the salt concentration increases the "osmotic" stress in the CNT-NMP system and, thus, decreases the stability of the CNT dispersions in NMP. Direct experiments confirm the simulation results: addition of NaI salt into the NMP dispersions of pristine CNTs leads to precipitation of CNTs (bundle formation) even at very small salt concentration (similar to 10(-3) mol L-1). In line with the simulation predictions, the effect increases with the increase of the salt concentration. Overall, our results show that dissolved salt ions have strong effects on the stability of CNT dispersions. Therefore, it is possible to stimulate the bundle formation in the CNT-NMP dispersions and regulate the overall concentration of nanotubes in the dispersions by changing the NaI concentration in the solvent

Aggregation kinetics of single-walled carbon nanotubes investigated using mechanically wrapped multinuclear complexes: probing the tube–tube repulsive barrier

“…We measured the CCC for NaBr in a NMP SWCNT dispersion, quiescent and in the dark, to be 5.5 AE 0.5 mM. This is consistent with similar studies of NaI in NMP during agitation by Frolov et al 58 Their work reports a qualitative description of dispersion stability consistent with what we have reported quantitatively for the NaBr, 31 and other inorganic salts. 59 In this paper we quantify the dispersion stability, X o , of SWCNTs in DMF and measure the slow RLCA kinetics of a homologous series of ruthenium complexes as a function of charge state and binding capabilities of the coagulant.…”

Electrochemical deposition of platinum within nanopores on silicon: Drastic acceleration originating from surface-induced phase transition

“…It was reported that the local structure of ionic liquid or organic solvent in a confined nanospace is substantially different from that in the bulk. [8][9][10] Recently, we have revealed experimentally and theoretically that the surface-induced hydration structure of platinum complex ions has large effects on the enhancement of platinum deposition within nanoporous a) Electronic mail: fukami.kazuhiro.2u@kyoto-u.ac.jp. b) Present address: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.…”

Synthesis and characterization of novel high-performance thin film nanocomposite (TFN) FO membranes with nanofibrous substrate reinforced by functionalized carbon nanotubes

“…1(a) shows the photo images of the MWCNTs (as received) and f-CNTs (after functionalization) in the PEI/NMP/DMF dope solution. The f-CNTs could well disperse in the solution while this phenomenon was not observed for the MWCNTs, presumably due to the polar-polar affinity and electrostatic repulsion of the -COOH on f-CNTs [33,34,38,39].…”