Incorporation and recovery of SWNTs through phase behavior and aggregates transition induced by changes in pH in a catanionic surfactants system

The phase behavior and aggregates induced by changes in pH in a sodium N-tetradecyl-maleimidepimaric carboxylate (C-14-MPA-Na)/cetyltrimethylammonium bromide (CTAB) system have been investigated using rheology and cryogenic transmission electron microscopy (cryo-TEM). Viscoelastic solutions at a pH between 6.40 and 1.41, opalescent blue solutions at a pH between 1.41 and 1.32 and aqueous surfactant two-phase systems (ASTPs) at a pH between 1.32 and 0.56 are formed sequentially. The microstructures in the viscoelastic solutions are wormlike micelles that partially transform to vesicles in the opalescent blue solutions. The aggregates in the upper phase of the ASTPs are vesicles and lamellar micelles, and in the lower phase are spherical micelles. Further, Single-walled carbon nanotubes (SWNTs) were successfully hybridized into the wormlike micellar viscoelastic solutions. cryo-TEM, UV -Vis-IR, near-infrared photoluminescence (NIR-PL) and UV-Vis spectroscopy were used to study the dispersion of SWNTs in the viscoelastic solutions, and the results showed SWNTs can remain dispersed for more than 6 months at pH 6.40. The results obtained from rheology showed that the hybridization of SWNTs will not affect the aggregates and viscoelasticity compared that to the native viscoelastic solution. Above more, the SWNTs could be recycled by the pH-switched phase behaviors between viscoelastic solutions and ASTPs. (C) 2018 Elsevier Ltd. All rights reserved.