Encapsulation of single-walled carbon nanotubes with asymmetric pyrenyl-gemini surfactants

Abstract

Whereas the encapsulation technology of surfactants coating on the surface of single-walled carbon nanotubes (SWCNTs) attracts much attention, the mechanisms of asymmetric surfactants interacting with the SWCNTs and their molecular structures are rarely reported. Herein, we report a molecular dynamics (MD) simulation study on the investigation of surfactant adsorption and induced colloidal stability onto different SWCNTs. The surfactant-based encapsulation system, originating from the complementary π-π stacking, is validated through two-dimensional number density maps. We find that the asymmetric pyrenyl-gemini surfactants (APGSs) form double-layer assembled architecture films on nanotube surface. The inner layers of the films are packed with the pyrenyl groups of APGSs, which interact with SWCNTs via π-π stacking, while the outer layers composed of alkyl chains of APGSs coat at the nanotube surface through van der Waals interactions. In addition, we observe a configurational transformation of APGSs on the SWCNT surface from the folding configuration to unfolding patterns, when increasing the nanotube radius or the surface coverage of APGSs. Our study provides helpful insights into the encapsulation mechanism of APGSs on the SWCNT surface and the design of highly selective dispersants for SWCNTs.