We investigate the synthesis and application of anisotropic hollow silica colloids as air voided opacity modifiers in dry polymer films in Chapter 1, with the aim of improving upon the light scattering efficacy of the commercially used isotropic hollow latex particles, ROPAQUE™. In order to generate anisotropic hollow silica particles we utilized a sacrificial templating method, ultimately leading us to investigate the opacifying power of hollow silica particles derived from a calcium carbonate template known as SOCAL P3. Initial investigations indicated that shell fragmentation and collapse of our “1st generation” hollow silica particles (with thin shells) led to a loss of opacity, as few air voids remained intact. Tuning the reaction parameters afforded hollow silica particles with thicker shells that displayed enhanced light scattering over the 1st generation hollow SiO2 particles and to SOCAL P3 when film thickness was accounted for. Chapter 2 is an extension of the work done in Chapter 1, wherein we aim to improve pigment dispersion (and consequently opacity) by grafting negatively charged, hydrophilic, polymer brushes to CaCO3@SiO2 particles. This confers enhanced colloidal stability to the particles through electrosteric stabilization. For this we first functionalize the surface with a tertiary alkyl bromide atom transfer radical polymerization (ATRP) initiator to furnish a surface capable of growing polymer brushes from. The initiator is anchored to the surface through siloxane bonds and an amide group, the latter to enhance hydrolytic stability over a wide pH range. We then used a SI-ATRP (where SI = surface initiated) in order to grow the polymer brushes, which we found to generate highly colloidally stable hollow SiO2 particles that demonstrate an enhanced contrast ratio to the sterically stabilized hollow SiO2-PVP particles used in Chapter 1. In Chapter 3 we investigate the multiple orientations of hematite superellipsoids (pseudocubes stabilized with PVP) trapped at an oil-water interface, through a combination of experiments and simulations. We find three orientations in all; two of which are thermodynamic minima and one which corresponds to a kinetically-trapped orientation. The latter results from some particles going through a negligible free energy gradient upon reorientation. Experimental and computational results for the relative balance of particle populations are found to be in excellent agreement with one another. We show that the final position of the particle is both a function of the free energy landscape and the precise orientation of the particle at the point of contact with the interface. A modified silica rod synthesis from an oil-in-water emulsion is demonstrated in Chapter 4, whereby we manage to asymmetrically include a manganese oxide head at one end of the rod to generate a colloidal “matchstick” morphology. Placing these particles into a solution of hydrogen peroxide as fuel facilitates their propulsion as they form an asymmetrical gradient of the breakdown products of hydrogen peroxide; water and oxygen. Adjusting fuel concentration alters the effective diffusion coefficient with a 1st order relationship. Furthermore, we demonstrate that these particles can undergo chemotaxis towards a higher concentration of fuel when placed into a fuel gradient. We rule out convection and other external forces as the reason for directional motion by simultaneously imaging catalytically inert microspheres which travel under convection in the opposite direction to that of the rods.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:595765 |
| Date | January 2013 |
| Creators | Morgan, Adam R. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/59755/ |
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