Morgan, Adam R. (2013) Synthesis, applications and phenomena of anisotropic inorganic colloids. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Colloids, Silica, Anisotropy, Light -- Scattering, Colloids -- Synthesis
Official Date:	October 2013
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Bon, Stefan Antonius Franciscus
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC); AkzoNobel; Advantage West Midlands (AWM); European Regional Development Fund (ERDF); Birmingham Science City
Extent:	xxxviii, 282 leaves : illustrations.
Language:	eng

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