α-Pyrene polymer functionalized multiwalled carbon nanotubes: Solubility, stability and depletion phenomena

This paper presents a study on the stability of dispersions of multiwalled carbon nanotubes that are covered with alpha-pyrene functionalized polymers prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization and dispersed in different solvents. We find that a rather small amount of these polymers (M-polymer/M-CNT less than 0.1) is capable of stabilizing a high concentration of CNTs (up to 2500 mg/l) in solution. Another strong evidence for well-stabilized CNTs is the comparably low gel points of around 1 vol% of CNTs in solution. We find that adding the alpha-pyrene functionalized polymer to CNTs has two counter playing effects: on the one hand, increased surface coverage of the carbon nanotubes increases their solubility; on the other hand increased concentration of free polymer in the solution enhances the depletion forces between the nanotubes. (C) 2008 Elsevier Ltd. All rights reserved.