Novel Polycyclic Aromatic Hydrocarbon Copolymer for Graphene Exfoliation and Functionalisation

Abstract

The production of large quantities of graphene by liquid phase exfoliation remains a significant challenge, which limits its application in device manufacture. The main objective of this work is to explore possible aqueous-based routes to solve this impasse. New amphiphilic copolymers containing polycyclic hydrocarbon (PAH) side chains were synthesised with a view to their utility as stabilisers for aqueous graphene dispersions. To this end a variety of perylene- and pyrene-containing copolymers were prepared by radical copolymerisation of 5-(perylen-3-yl)pent-4-yn-1-yl methacrylate (PePnUMA, 33), 1-pyrenemethyl methacrylate (PyMMA, 26) with either 2-acrylamido2-methylpropane sulfonic acid (AMPS, 27) or 2-(2-bromoisobutyryloxy)ethyl methacrylate (BIEM, 53). The first study examines the ability of PAH copolymers to stabilise graphene in aqueous solution at varying stabiliser concentration. The performance of PAH stabilisers was investigated by studying the dispersion concentration and stability using UV-vis spectroscopy, Xigo Acorn Area NMR and zeta potential measurements. The initial results suggest the performance of PAH polymeric stabilisers are enhanced with increasing molar ratio of PAH moieties in the polymer composition. Substitution of the aromatic core from pyrene to perylene resulted in an improved exfoliation and stabilisation efficiency of the dispersing agent at constant stabiliser (3 mg/mL). The second study describes the development of reliable approaches for the growth of strongly bound polymer brushes to a silicon surface and CVD graphene. This was achieved using copolymers containing side chain polycyclic hydrocarbon (PAH) moieties incorporating BIEM (atom transfer radical polymerisation initiator), deposited using a high-resolution super inkjet printer. The growth of poly(hydroxyethyl methacrylate) and poly(N-isopropylacrylamide) brushes was demonstrated, establishing a new route for surface modification of CVD graphene.