Investigating the preparation of sterically-stabilised latexes and polymer/graphene oxide nanocomposite particles

Abstract

This thesis describes the preparation of anionic, non-ionic and cationic sterically-stabilised poly(benzyl methacrylate) latex nanoparticles via reversible addition-fragmentation chain transfer (RAFT) polymerisation and polymer/graphene oxide nanocomposite particles via heteroflocculation. Anionic sterically-stabilised poly(potassium 3-sulfopropyl methacrylate)-poly(benzyl methacrylate) (PKSPMA-PBzMA) diblock copolymer nanoparticles were prepared via RAFT-mediated polymerisation-induced self-assembly (PISA) in alcohol/water mixtures. The effect of solvent quality (alcohol/water ratio and co-solvent composition) on the formation of these nanoparticles was investigated. Generally, particles with larger diameter were obtained using higher alcohol content, indicating the solvency of stabiliser and core-forming block can influence the aggregation of polymer chains during self-assembly. Small-angle X-ray scattering (SAXS) studies showed that these particles had diverse structural parameters. This protocol was successfully extended for the preparation of anionic sterically-stabilised poly(4-styrene sulfonate)-poly(benzyl methacrylate) (PSS-PBzMA) diblock copolymer nanoparticles. It was demonstrated for the first time that non-ionic sterically-stabilised poly(benzyl methacrylate) (PBzMA) nanoparticles can be prepared via RAFT miniemulsion polymerisation. This was achieved using relatively hydrophobic RAFT agent and non-ionic Lutensol TO 20 surfactant. The effects of hydrophobe, initiator and RAFT agent concentrations on particle diameter, particle number, rate of polymerisation (Rp) and molar mass of the final latexes were investigated. Increasing hydrophobe increased number of particles, but decreased latex diameter. Increasing initiator increased overall Rp and followed a power-law relationship Rp [initiator]1/2, but negligible differences in molar mass and particle diameter were observed. In contrast, increasing RAFT agent increased the latex diameter and the overall Rp. In most cases, well-controlled RAFT polymerisations were achieved, as judged by kinetic studies. Cationic sterically-stabilised poly(2-vinyl pyridine)-poly(benzyl methacrylate) (P2VP-PBzMA) diblock copolymer nanoparticles were prepared via RAFT-mediated PISA under emulsion polymerisation conditions. Nanoparticles with tuneable diameters could be prepared by altering the DP of the stabiliser (P2VP) and/or the core-forming block (PBzMA), or simply by varying the solution pH for a fixed target copolymer composition. Varying the solution pH resulted in the P2VP stabiliser having different solubilities due to protonation/deprotonation of the pyridine groups, leading to a noticeable effect on the aggregation of polymer chains during PISA process. These P2VP-PBzMA nanoparticles had good colloidal stability and high cationic charge below pH 5 and can be dispersed over a wide pH range. Finally, polymer/GO nanocomposite aggregates with core/shell morphologies were prepared via electrostatically-induced heteroflocculation at room temperature in either acidic (pH 2) or basic (pH 9) conditions. Control heteroflocculation experiments were conducted using the previously prepared anionic PKSPMA-PBzMA and non-ionic PBzMA nanoparticles to demonstrate no adsorption of GO nanosheets. In contrast, positively charged P2VP-PBzMA and poly(ethylene glycol) methacrylate (PEGMA)-stabilised P2VP latexes were used for the adsorption of negatively charged GO nanosheets. The degree of flocculation and the strength of electrostatic interaction of the polymer/GO nanocomposite particles were assessed using disc centrifuge photosedimentometry (DCP). DCP and TEM studies suggested that the optimal GO loading was approximately 20% w/w based on latex and P2VP-PBzMA/GO may have stronger electrostatic attraction.

Date of Award	31 Dec 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Saunders (Supervisor) & Lee Fielding (Supervisor)