Established chirality separation techniques for single-wall carbon nanotubes (SWNTs) in aqueous suspensions make use of chirality specific adsorption behavior of surfactants on these nano-carbon surfaces. Here, we investigate the adsorption of sodium cholate on SWNTs of different chirality with diameters ranging from 0.7 to 1 nm. Titration studies are performed at different temperatures by measuring photoluminescence emission energies of the diluted SWNT suspensions. The high sensitivity of the exciton to its environment allows to detect small changes in arrangement and concentration of surfactants on the SWNT surface, as recently shown for the (6,5) chirality by Bergler et al. [1]. Here we report on substrate-induced cooperative adsorption regimes for sodium cholate on five different SWNT chiralities. The critical micelle concentrations of the cholate-SWNT micelles exhibit a linear increase with SWNT diameter, while the thermodynamic stability of the cholate-SWNT micelles decreases. These diameter and temperature dependences may play a key role in the separation of SWNT chiralities by density gradient ultracentrifugation and aqueous two phase extraction and thus may help not only to understand the microscopic sorting mechanisms but also to improve empirical preparation protocols.

[1] Bergler et al., Langmuir 2016, 32, 9598-9603, DOI: 10.1021/acs.langmuir.6b02759