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Colloidal phoretic motion



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Rees-Zimmerman, Clare Rebecca 


Phoretic motion refers to the transport of particles up or down the concentration gradient of a different solute and can be exploited to control particle motion. This thesis seeks to understand the relative importance of different phoretic effects. It examines phoretic motion in the context of concentration gradients in a drying film, to understand which phenomena govern the stratification of particles in the final dried structure. A colloidal hydrodynamic model valid up to near close-packing, is derived and solved numerically to model diffusion, excluded volume diffusiophoresis, hard sphere and Derjaguin–Landau–Verwey–Overbeek (DLVO) interactions in a drying film. Excluded volume diffusiophoresis is found to act to promote small-on-top stratification, causing fluxes of a similar magnitude to diffusion. The hard sphere interaction model predicted regimes with small- or large- on-top stratification, in addition to a new small-large-small sandwich layering regime. However, its predictions did not quantitively agree with x-ray scattering results of dried silica and latex films. A Hele-Shaw cell experiment measured the flux of latex particles down a concentration gradient of silica particles. The latex motion was arrested by increasing salt concentration, consistent with electrolyte diffusiophoresis driven by silica and its stabilising counterion. This also implies that electrolyte diffusiophoresis is more significant than excluded volume diffusiophoresis for these colloids. The DLVO interaction model showed that by setting the particle surface potentials and salt concentration, we can select either small- or large- on-top or no stratification. Overall, we learn the importance of interactions and electrolyte-driven diffusiophoresis, overlooked in favour of hard sphere interactions and excluded volume diffusiophoresis in the literature, with further work suggested in modelling electrolyte-driven diffusiophoresis in drying films.





Routh, Alex


Colloidal hydrodynamics, Diffusiophoresis, Diffusion, Colloidal interactions, Multivalent electrolytes, Stratification, Drying films


Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Ernest Oppenheimer Fund