Understanding the self-assembly of surfactants on the surface of single-walled carbon nanotubes (SWCNT) is important to decipher and improve separation techniques of metallic and semiconducting SWCNT and their application in nano electronics and sensing. In this study, we report direct spectroscopic measurements of the macromolecular organization of surfactant ordering using different concentrations of sodium dodecyl sulfate (SDS) encapsulated with defendant diameter (6,5) and (7,6) semiconducting SWCNTs with and without excess electrolytes within solution-processed thin films. By using vibration Sum Frequency Generation Spectroscopy (VSFG), sensitive measurements of interfacial surfactant ordering, we find that as the bulk SDS concentration increases near the surfactant critical micelle concentration (CMC) the interfacial order increases as well, independently of SWCNTs diameter.However, at higher surfactant concentration measured here, the (6,5) SWCNTs produce more ordered structures relative to those with (7,6) SWCNTs. The relatively larger diameter (7,6) chiral tubes support enhanced van der Waals (vdW) interactions between the tube surface and the surfactant alkyl chain groups that increase the density of gauche defects. A new effect arises when the precursor solution is exposed to a small concentration of divalent Ca2+counterions. We postulate that the salt bridging configuration on such highly curved surfaces decreases the ordering of interfacial surfactant molecules. However, this phenomenon was not observed with excess Na+ ions at the same ionic strength, where instead a modest increase in surfactant ordering was observed with the excess monovalent electrolyte. These results provide significant insights for solution processing of vdW nanomaterials and demonstrate that VSFG is a sensitive probe of nanostructured.

Tuning the surface ordering of self-assembled ionic surfactants on semiconducting single-walled carbon nanotubes: Concentration, tube diameter, and concenterions

2019 Spring National Meeting

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