Novel Methods for Functionalising Graphene Materials with Polymers

Abstract

Grafting polymers on graphene flakes is a promising technique to tune the properties of flakes and improve the stability of the dispersion, which expands the applications of graphene materials in more fields. However, functionalisation of graphene materials to introduce initiator groups or polymerisable groups on surface is an essential and challenging step due to chemical inertness and poor dispersion stability in most solvents. In recent years, functionalisation has been intensively studied either through the formation of strong chemical binding with graphene surface or through noncovalent interaction such as pai-pai interaction, electrostatic force, or hydrogen bonds etc. In this thesis, due to a good compromise between the degree of functionalisation and the disruption of aromatic structure, Diels-Alder reactions as covalent functionalisation methods were applied to reduced graphene oxide (rGO) and graphene nanoplatelets (GNP), which introduced either 6-8 wt. % initiator groups (-Br) for controlled polymerisation by ARGET ATRP ('grafting from' method) or polymerisable groups (-C=C) for free radical polymerisation ('grafting through' method). Afterwards, two types of polymers were successfully grafted on DA reaction functionalised graphene with around 15 wt. % polymer by 'grafting from' and 'grafting through' methods. These two grafting methods were further compared through element mapping. On the other hand, noncovalent functionalisation was studied on rGO through the adsorption of polyelectrolytes via layer-by-layer assembly. To study the stability of adsorption via electrostatic force, commercial polymer poly(diallyldimethylammonium chloride) (PDADMAC) and synthesised copolymer poly(2-methacryloxyethyl trimethyl ammonium chloride -co-hydroxyethylmethacrylate) (PMH) as the first layer on rGO was compared by zeta potential measurement during washing cycles. Polystyrene sulfonate (PSS) and polyallylamine (PAA) as the second layer were compared on PDADMAC-coated rGO which shows more stable adsorption than PMH. The formation of a bilayer of PDADMAC-PSS on rGO shows high stability adsorption and is of comparable bond energy to single chemical bonds determined by ITC thermodynamic analysis. Hence, a macroinitiator containing similar anionic structure units to PSS and -Br initiator groups was used as the second layer, which introduced 6.6 wt.% initiator groups after adsorption on rGO surface. PMEATC polymers were grafted from functionalised rGO and PMETAC-grafted rGO with around 52 wt. % polymers exhibit high stability in water dispersion.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stephen Edmondson (Supervisor) & Suelen Barg (Supervisor)