Probe diffusion of single-walled carbon nanotubes in semidilute solutions of polyacrylonitrile homo- and copolymers: Effects of topological constraints and polymer/Nanorod interactions

Abstract

With varying the molecular weight, copolymer chemical structure and concentration, the probe diffusion behavior of single-walled carbon nanotubes (SWCNTs) in N, N-dimethylacetamide (DMAc) solutions of polyacrylonitrile (PAN) was studied by dynamic light scattering (DLS) technique. In combination with the systematic viscosity property investigation for PAN/DMAc system, the probe diffusion results provided insight to understand the interactions between PAN and SWCNTs. It was found that, due to depletion interaction, the SWCNT diffusion positively deviates from the Stokes-Einstein (SE) relation in PAN homopolymer solutions. However, in PAN copolymer solution, the SWCNT diffusion mostly obeys the SE relation, which was speculated as a result of hydrogen-bonding formation between the carboxylic acid functional groups in PAN copolymers and on purified SWCNTs. Moreover, due to the unique features of SWCNT probes - very long, extremely rigid, and adjustable bundle diameter, the SWCNT probe diffusion unambiguously revealed the topological constraints of polymer network responsible for the retardation of thin rod diffusion. Quantitative analysis indicated that the correlation length rather than the “tube” diameter of polymer liquid is the critical length scale to dictate the diffusion retardation of SWCNTs in polymer solutions.