Dispersion of multiwalled carbon nanotubes (MWCNTs) by ionic liquid-based Gemini pyrrolidinium surfactants in aqueous solution

Gemini pyrrolidinium surfactants ([C (n) py-4-C (n) py][Br-2]) are a new kind of ionic liquid-based Gemini surfactants. Multiwalled carbon nanotubes (MWCNTs) can be dispersed effectively in [C (n) py-4-C (n) py][Br-2] aqueous solution. The resulting MWCNT suspensions are stable for more than 1 month, and no precipitation is observed. Ultraviolet-visible-near infrared (UV-Vis-NIR) spectra are performed to determine the dispersion of MWCNTs and the optimal concentration (C (opt)) of [C (n) py-4-C (n) py][Br-2]. Compared with C (n) MPB, [C (n) py-4-C (n) py][Br-2] is more effective in dispersing MWCNTs. It was also observed that [C (n) py-4-C (n) py][Br-2] with a longer hydrocarbon chain displays a stronger dispersion ability. The adsorption of [C (n) py-4-C (n) py][Br-2] on MWCNTs is investigated by zeta-potential and surface tension measurements. The zeta-potential results show that MWCNTs dispersed in [C (n) py-4-C (n) py][Br-2] aqueous solution have relatively high positive charges. It is the electrostatic repulsion force between the MWCNTs which makes them stable. Furthermore, a possible dispersion mechanism is proposed.