Use of a Chondroitin Sulfate Isomer as an Effective and Removable Dispersant of Single‐Walled Carbon Nanotubes

Abstract Three isomers of chondroitin sulfate (CS), i.e., CS‐A, CS‐B, and CS‐C, are investigated as nanotube dispersants and are found to have vastly different abilities to disperse single‐walled carbon nanotubes (SWNTs) in water due to their different intramolecular interactions. Only CS‐A and CS‐C effectively disperse SWNTs into small bundles or individual tubes while CS‐B disperses SWNTs poorly. Computer simulation and circular dichrosim show that neat CS‐A and CS‐C have weak intramolecular hydrogen bonding and extended conformations in solution resulting in energetically more favorable interactions with nanotubes. CS‐B has relatively strong intramolecular Coulombic interaction and more alpha‐helical secondary structure in solution resulting in energetically less favorable interaction with the nanotubes. Atomic force microscopy images show helical wrappings of CS‐A and CS‐C around the SWNTs. Transmission electron microscopy corroborates the helical wrapping of CS‐A. Different isomeric forms of a polymer can have vastly different dispersing power because of their different intramolecular interactions and conformations. The easy removability of CS‐A from nanotubes is confirmed with X‐ray photoelectron spectroscopy showing almost no detectable sulphur content after washing with water and by application of washed CS‐A dispersed SWNTs in field‐effect transistors.