Date of Original Version
Single-walled carbon nanotubes’ (SWNT) effectiveness in applications is enhanced by debundling or stabilisation. Anionic surfactants are known to effectively stabilise SWNTs. However, the role of specific chirality on surfactant-stabilised SWNT aggregation has not been studied to date. The aggregation behaviour of chirally enriched (6,5) and (7,6) semiconducting SWNTs, functionalised with three anionic surfactants – sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and sodium deoxycholate – was evaluated with time-resolved dynamic light scattering. A wide range of mono- (NaCl) and divalent (CaCl2) electrolytes as well as a 2.5 mg total organic carbon (TOC) L–1 Suwannee River humic acid were used as background chemistry. Overall, sodium dodecyl benzene sulfonate showed the most effectiveness in stabilising SWNTs, followed by sodium deoxycholate and sodium dodecyl sulfate. However, the larger diameter (7,6) chirality tubes (compared to (6,5) diameter), compromised the surfactant stability due to enhanced van der Waals interaction. The presence of divalent electrolytes overshadowed the chirality effects and resulted in similar aggregation behaviour for both the SWNT samples. Molecular modelling results elucidated key differences in surfactant conformation on SWNT surfaces and identified interaction energy changes between the two chiralities to delineate aggregation mechanisms. The stability of SWNTs increased in the presence of Suwannee River humic acid under 10 mM monovalent and mixed-electrolyte conditions. The results suggest that change in chirality can overcome surfactant stabilisation of semiconducting SWNTs. SWNT stability can also be strongly influenced by the anionic surfactant structure.
Khan Iftheker A., Flora Joseph R. V., Afrooz A. R. M. Nabiul, Aich Nirupam, Schierz P. Ariette, Ferguson P. Lee, Sabo-Attwood Tara, Saleh Navid B. (2015) Change in chirality of semiconducting single-walled carbon nanotubes can overcome anionic surfactant stabilisation: a systematic study of aggregation kinetics. Environmental Chemistry 12, 652-661.
Available at: https://doi.org/10.1071/EN14176