Influence of Electrostatic Interactions on Spin-Assembled Single-Walled Carbon Nanotube Networks on Amine-Functionalized Surfaces
Preferential interactions between self-assembled monolayers (SAMs) terminated with amine functional groups and single-walled carbon nanotubes (SWNTs) were exploited to produce nanotube networks (SWNTnts) via spin coating. We provide insight into the mechanisms of this system while simultaneously demonstrating a facile approach toward controllable arrays of SWNTnts. The chirality, density, and alignment of the SWNTnt was heavily influenced by adsorption onto amine-functionalized surfaces that were exposed to varying pH solutions, as evidenced by atomic force microscopy (AFM) and Raman spectroscopy. This pH treatment altered the charge density on the surface, allowing for the examination of the contribution from electrostatic interaction to SWNT adsorption and SWNTnt characteristics. Secondary and tertiary amines with methyl substitutions were utilized to confirm that adsorption and chirality specific adsorption is largely due to the nitrogen lone pair, not the neighboring hydrogen atoms. Thus, the nature of adsorption is predominantly electrostatic and not due to van der Waals forces or localized polarization on the SWNTs. Moreover, the overall density of SWNTnts is different for the various amines, indicating that the accessibility to the lone pair electrons on the nitrogen plays a crucial role in SWNT adsorption. With greater understanding of the amine-SWNT interaction, these findings can be utilized to control SWNTnt formation for the precise integration into electronic devices.