Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439958
Title: Microcapsules with liquid cores and solid shells for pressure release applications
Author: O'Sullivan, Michael Francis
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2007
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Abstract:
The encapsulation of one material by another, to form core-shell particles, has many applications: principally the containment, protection, and distribution of an active material. This thesis describes the development of core-shell particles with liquid cores and solid shells of tunable thickness. Two main systems are studied. Firstly, polydimethylsiloxane (PDMS) emulsions, or microgels if cross-linked, are employed as templates for the formation of solid shells. The templates are prepared by a surfactant-free emulsion polymerization of dimethyldiethoxysilane (DMDES) that allows monodisperse emulsions to spontaneously form, subject to appropriate monomer concentrations. The viscosity of the microgel is controlled by variation of the cross-linking component's concentration. Silica shells were grown upon silica-skinned templates in a seeded growth process through slow addition of tetraethoxysilane (TEOS) under basic and ethanolic conditions. Solid silica-silicone composite shells were formed, in the absence of ethanol, through condensation of TEOS and DMDES. Shell thickness may be controlled by manipulation of relative TEOS and DMDES concentrations, or by quenching the shell maturation step. The second system involves the encapsulation of acidic or basic water-in-hexadecane emulsions. These are prepared and exposed to small quantities of TEOS, thereby forming a thin silica membrane at the water/oil interface. This skin was observed to crenellate, with an optical microscope, upon evaporation of the aqueous core. Similar particles were also prepared from emulsions initially stabilized with hydrophobic fumed silica. Thicker membranes may be prepared if the aqueous phase also contains alkoxysilane monomer; these skins survive washing with heptane, or centrifugation into water, and may be viewed by SEM. The coated PDMS particles were subjected to compression using a micromanipulator. The capsule breaking force was found to be proportional to the shell thickness, as quantified using SEM and ultramicrotomy. Model actives, such as dyes, may be incorporated into the PDMS templates prior to shell formation through use of a vector solvent that swells the core material.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.439958  DOI: Not available
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