Direct Imaging of Carbon Nanotubes in Super Acid Solutions and Liquid Crystalline Phases

Olga Kleinerman, Chemical Engineering, Technion, Haifa, Israel
Lucy Liberman, Chemical Engineering, Technion, Haifa, Israel
Amram Bengio, Chemical And Biomolecular Engineering, Rice University, Houston, Usa
Yachin Cohen, Chemical Engineering, Technion, Haifa, Israel
Yeshayahu Talmon, Chemical Engineering, Technion, Haifa, Israel

In applications of carbon nanotubes (CNTs), the goal is to retain in the final product the electronic and mechanical properties of the individual CNT. To achieve this goal one needs to separate the as-produced entangled CNTs, held together by strong van der Walls interactions.

Our research relies on CNTs separation by their dissolution in chlorosulfonic acid (CSA) 1, which is BrØnsted superacid. CSA dissolves long CNTs up to high concentrations (>10 wt. %). The dissolution is governed by a reversible protonation mechanism, and yields neither covalent functionalization of the CNT sidewalls, nor wall damage. CNT arrangement in these thermodynamically stable solutions could be tuned by CNT concentration, as in the case of rigid-rod polymers. 

Cryogenic Electron Microscopy (cryo-EM) is the only tool for direct imaging of CNT aggregates nanostructure in superacid, tracking of phase transitions in “as-prepared” solutions, as a function of CNT type and concentration. Cryo-EM specimen preparation for CNT/superacid systems requires absolute separation of solutions from water (including humidity) and organic materials. Cryo-EM imaging is performed under stable cryogenic temperature, using a low-electron-dose mode, combined with controlled depletion of superacid from CNT surface 2.

 1. Davis, V.A. et al., True solutions of single-walled carbon nanotubes for ‎assembly into macroscopic materials. Nature Nanotechnol. 4, 830-834, (2009).

2. Kleinerman, O. et al., Cryogenic-Temperature Electron Microscopy Direct Imaging of Carbon Nanotubes and Graphene Solutions in Superacids. J. Microsc.  259, 16–25, (2015).

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