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Title: Driven colloidal particles in optical potential energy landscapes
Author: Abbott, Joshua
ISNI:       0000 0004 7960 0040
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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The dynamic behaviour of colloidal particles driven across one-dimensional optical potential energy landscapes is studied. Colloids are driven with a piezo-stage, manipulated with optical tweezers and magnetic fields and imaged using optical microscopy. First, the meta-stable horizontal and vertical states of a colloidal rod in a single optical trap close to a flat wall are explored. A colloidal rod is then driven through a periodic optical potential energy landscape. The equilibrium position of a rod driven below the critical velocity is found to vary substantially from that of a sphere due to the friction coefficient of a rod being highly dependent on its proximity to an optical trap. At higher velocities, a colloidal rod is shown to act similarly to a colloidal sphere, exhibiting dynamic mode locking. Colloidal spheres are then driven across a time-dependent one-dimensional optical potential energy landscape with different modes of dynamic mode locking being observed. The mode locked step width is shown to vary with the oscillation frequency and the coupling strength between the particle and the optical landscape. The particle transport across the time-dependent landscape is also studied by measuring the effective diffusion coefficient which is highly sensitive to the driving velocity and mode locking. Next, chains of interacting colloidal particles are driven through a time-independent optical potential energy landscape. A mismatch between the length scales of the chain and the landscape gives rise to a freely sliding chain in an Aubry-type transition. In this regime a chain exhibits zero static friction despite being subject to a potential energy landscape. Chain motion is inspected for a driven flexible chain that is seen to exhibit breathing modes. Introducing oscillations in the driving force leads to dynamic depinning, which is affected by both the frequency and amplitude of the oscillations. Finally, the stochastic thermodynamics for particles driven across an optical landscape is considered. The work done by a particle in both a time-independent and a time dependent optical landscape is measured. The optical work in a time-independent landscape is shown to be zero. However, the time-dependent counterpart exhibits a finite amount of work due to the optical landscape. The magnitude of the observed total work is considered in light of the mechanism of particle motion along with analysis of the contributing optical work and driving work.
Supervisor: Dullens, Roel Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Colloids--Optical properties