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Utilising phase separation : the study of macromonomer stabilised colloids for thermal energy storage and thermoresponsive polymers for optical devices
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Booth, Joshua R. (2021) Utilising phase separation : the study of macromonomer stabilised colloids for thermal energy storage and thermoresponsive polymers for optical devices. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3765846
Abstract
This thesis encompasses the study of the effectiveness of ω-unsaturated macromonomers as reactive stabilisers in emulsion and miniemulsion polymerisation, the development of a nanocapsule dispersion with tuneable thermal regulation properties and the manufacture of a low-temperature warning system using bespoke polymer solutions. The common thread that weaves through this work is self-assembly and phase separation. Along this journey, several interesting observations and results have emerged. Many of which are explored in depth, new theories are presented and comparisons to published research are drawn.
In chapter 2, amphiphilic, block copolymer, stabilisers are synthesised by a two-stage emulsion polymerisation process. The surprisingly broad size distribution of the macromonomer latex after the first step and evidence of secondary nucleation in the second step are investigated. The macromonomers are used as an aqueous dispersion of micelles to stabilise latexes with particles diameters <100 nm. The latexes are colloidally stable at 30 % w/w solids using macromonomer loadings as low as 0.5 wt % with respect to monomer.
In chapter 3, the macromonomer stabilisers are used in miniemulsion polymerisation. Interfacial tension measurements revealed the slow dynamics of their adsorption at liquid-liquid interfaces. In miniemulsion polymerisations with less than full droplet coverage of the stabiliser, monomer exchange between growing particles leads to the formation of dimpled particles. In reactions with an excess of micelles, flocculation of droplets after high-shear homogenisation causes bimodal size distributions. To address the issue of poor molecular weight control, a semibatch miniemulsion procedure is devised. The system appears diffusion-limited and the low monomer concentration allows for controllable chain growth.
In chapter 4, nanocapsules containing phase change materials (PCM), to be used as latent functional thermal fluids, are synthesised by miniemulsion polymerisation. The effect of crosslinking and monomer hydrophobicity on capsule formation and core phase change behaviour is investigated. The study culminates in the synthesis of a latex containing a mixture of n-octadecane and n-docosane crosslinked poly(methyl methacrylate) nanocapsules. As the two n-alkanes are encapsulated in separate reactions, their phase transitions occur independently. Regulation of temperature is found to be greater in the aqueous PCM dispersion compared to the base fluid.
In chapter 5, the focus shifts from phase change materials to phase separation of polymer solutions. The goal is to produce an optical device that warns the user of low temperatures. Firstly, the phase separation of the system is tailored by adjusting polymer weight fraction and molar mass. A highly flexible, multi-layer device, with a fast and reversible optical response around zero degrees Celsius is produced. For use in the dark, two concepts are devised that utilise aggregation-induced emission (AIE). A dual-layer style device uses the viscosity increase of a glassy polymer matrix, whereas a single-layer type device relies upon polymer phase separation to restrict the molecular motion of the AIE-gen.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics Q Science > QD Chemistry |
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Library of Congress Subject Headings (LCSH): | Emulsion polymerization, Stabilizing agents, Separation (Technology), Colloids, Nanocapsules, Phase transformations (Statistical physics) | ||||
Official Date: | December 2021 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Bon, Stefan Antonius Franciscus | ||||
Format of File: | |||||
Extent: | xxxii, 264 leaves : illustrations | ||||
Language: | eng |
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