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Title: Anisotropic colloids : from synthesis to transport phenomena
Author: Longbottom, Brooke W.
ISNI:       0000 0004 7972 4174
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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This thesis is based around the theme of how anisotropy in colloidal shape can afford interesting transport phenomena. The term 'transport phenomena' is used in a broad sense to represent transport processes over length scales ranging from nanometers up to micrometers. We begin by looking at the simple case of Brownian motion of polymer microscopheres and investigate the effect of roughening their surface. A fabrication protocol is presented for tuning the surface roughness by deforming the polymer microspheres in the presence of select inorganic colloidal particles. The scale of roughness imparted is a function of the deformation time and the dimensions of the inorganic particles. Despite a large scale of roughness in comparison to the 'smooth' polymer microspheres, the noslip boundary condition holds and the Brownian motion is modelled exceptionally by the Stokes-Einstein-Sutherland relation. We then move on to look at the phoretic propulsion of these roughened objects by first post-modifying the particles with a sputtered platinum cap and subsequently tracking particles dispersed in hydrogen peroxide solution. Those with smaller surface deformations were found to propel at ∼2× the velocity of 'smooth' particles and additionally some displayed interesting rotary, angular propulsion. We also present a different design for a self-propelling colloid in the form of a silica-manganese oxide 'matchstick' shaped particle of which the aspect ratio can be carefully tuned by monitoring reaction kinetics. We find that the propulsive velocity of the matchstick particles is limited by a silica coating around the catalytic manganese oxide, and thus particles display only enhanced diffusion when dispersed in hydrogen peroxide fuel. Finally we make our way down to the nanoscale and quantify the transport mean free path of white light for colloidal films of silica 'rod' and 'worm'-like colloids to probe the material whiteness. This study, inspired by one of nature's whitest known thin materials - the Cyphocilus beetle shell - shows that anisotropy of scattering centres can lead to excellent whiteness properties.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry