Sythesis and characterization of polyelectrolytes for functionalization of carbon nanotubes

Abstract

Two polyelectrolytes were synthesized with reversible addition-fragmentation chain transfer (RAFT) polymerization and Grignard metathesis (GRIM) polymerization for the functionalization of carbon nanotubes. The responses of functionalized carbon nanotubes towards different substrates were well studied.

A diblock polyelectrolyte with methacrylic acid containing block and pyrene pendant block was synthesized by RAFT polymerization. The pyrene pendant block anchored on the surface of carbon nanotubes while the methacrylic acid containing block dissolved in methanol to disperse individual carbon nanotubes. The dispersed carbon nanotubes have shown morphological responsive towards substrates with pyridine groups and amino groups on surface. The thickness of functionalized carbon nanotubes on these substrates increased from tens of nanometers to hundreds of nanometers due to the swelling of the methacrylic acid containing block. The methacrylic acid units were deprotonated by pyridine groups and amino groups on the surface so the polymer chains in the methacrylic acid containing block stretched into rigid rod structure leading to the swelling effect.

A polythiophene-based conjugated polyelectrolyte with positive quaternary ammonium species on its side chains was synthesized by GRIM polymerization. The self-assembly behaviors of this conjugated polyelectrolyte in solvents with different polarities led to solvatochromism and different efficiencies for dispersion of carbon nanotubes. The efficiency of this conjugated polyelectrolyte for the dispersion of carbon nanotubes was highest when no aggregation was formed. The functionalized carbon nanotubes could be deposited on conductive substrates applied with negative potential due to the positive quaternary ammonium species. The density of carbon nanotubes deposited on the substrate increased with the potential applied. The electro-deposition of this functionalized carbon nanotubes could be applied for large scale fabrication of carbon nanotubes thin film.