Preparation and characterisation of nanomaterial containing copolymer worm gels

  • Qi Yue

Student thesis: Phd

Abstract

In this thesis various 2D/0D nanomaterial [including graphene oxide (GO), graphene nanoplatelets (GNP), silver flakes, and iron oxide nanoparticles] containing block copolymer nanocomposite worm gels were prepared. This was achieved using either in situ polymerisation-induced self-assembly (PISA) via reversible addition-fragmentation chain-transfer (RAFT) polymerisation in the presence of nanomaterial, or physically mixing the nanomaterial into copolymer dispersions at a temperature where the copolymer exists as spherical micelles before returning to worm-like micelles when returned to room-temperature. The physical and functional properties of these materials were investigated and potential applications demonstrated. Firstly, aqueous poly(glycerol monomethacrylate)-b-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) and methanolic poly(glycerol monomethacrylate)-b-poly(benzyl methacrylate) (PGMA-PBzMA) worm gels were prepared by RAFT-mediated PISA. The former system undergoes a reversible worm-to-sphere degelation transition upon cooling to 5°C whilst the latter system undergoes the same transition on heating to 56°C. This transition allows these copolymer dispersions to be readily mixed with GO whilst in a low viscosity state and form nanocomposite gels on returning to room temperature via a sphere-to-worm transition. Various quantities of GO were added to the studied copolymer dispersions at a fixed copolymer content of 15% w/w. A general trend was observed whereby relatively small quantities of GO caused the gel strength of the nanocomposite gel to be higher than that of the pristine worm-gel, as determined by oscillatory rheology. Additional quantities of GO resulted in gel weakening or prevented gel-reformation altogether. A combination of aqueous electrophoresis and transmission electron microscopy measurements were used to investigate the mechanism of nanocomposite gel formation. GO containing block copolymer nanocomposite hydrogels formed from PGMA-PHPMA worm gels were also prepared via in-situ RAFT PISA of HPMA in the presence of a PGMA macromolecular chain-transfer agent and GO flakes. Composite copolymer worm gels containing 15 to 25% w/w copolymer and 0 to 8% w/w GO, based on copolymer, were investigated the maximum gel strength measured was a fifteen-fold increase over the same copolymer gel without the addition of GO. The nanocomposite gels were found to recover efficiently after the application of high shear, with up to 98% healing efficiency within seconds. These gels were demonstrated to be 3D printable, self-healing, adhesive and temperature responsive on cooling and re-heating. Multifunctional magnetic composite worm gels were prepared whereby various amounts of iron oxide and sodium chloride were incorporated into PGMA-PHPMA and PGMA-PHPMA/GO dispersions at low temperature and mixed with the high-speed mixer. The optimal concentration of iron oxide enhanced the gel strength of the nanocomposite gels which exhibited a strong magnetic response when a magnetic field was applied. These materials retained their thermo-response due to the presence of PGMA-PHPMA and were demonstrated to act as strain sensors. The measured electrical conductivity of the nanocomposite gels changed with applied strain and live/dead assays indicated that these nanocomposite gels have good biocompatibility. Finally, RAFT in-situ polymerisation was used to synthesise GNP containing nanocomposite copolymer worm gels. The maximum gel strength was 1.4 times higher than 20% w/w GO-containing copolymer worm gels synthesised by the same method and they showed high healing efficiency and self-healing behaviour. However, these 20% w/w GNP based on copolymer nanocomposite gels lose their temperature response. In this case, to further improve the conductivity, silver flakes can be added during the process of reconstituting the worm gel at low temperature after freeze-drying. After dehydration, the composite can serve as a recyclable highly condu
Date of Award31 Dec 2023
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorStephen Edmondson (Supervisor) & Lee Fielding (Supervisor)

Keywords

  • worm gels
  • RAFT
  • PISA
  • muti-fuctional responces
  • soft matter

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