Cresol-Carbon Nanotube Charge-Transfer Complex: Stability in Common Solvents and Implications for Solution Processing

The charge-transfer complex between cresol molecules and carbon nanotubes is confirmed by ¹H-nuclear magnetic resonance, Raman, and Fourier transform infrared spectroscopic studies. The stability of the cresol-nanotube complex in common solvents is determined by their dielectric constants. In solvents with high dielectric constants (>15), this non-covalent interaction is screened and the complex is destabilized, resulting in nanotube aggregation. In solvents with low dielectric constant (<10), the complex remains stable and the nanotubes are well dispersed. Therefore, using cresols as a minority cosolvent, surfactant-free dispersion of unfunctionalized single-walled and multi-walled carbon nanotubes in common industrial solvents can be achieved. This cosolvent strategy makes it possible to customize nanotube formulations in volatile industrial solvents for high-throughput solution-processing techniques, such as airbrushing. On the other hand, since high-dielectric-constant solvents, such as acetone, can destabilize the cresol-nanotube complex, they can be used for the benefit of removing any residual cresols without heating, resulting in clean carbon nanotube films.