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Title: A study of dynamics in microscopic systems using optical tweezers : dynamical stabilisation, cell stretching and thermal fluctuations
Author: Smart, Thomas James
ISNI:       0000 0004 7232 2076
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2018
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This thesis presents an investigation into the dynamics of three distinct microscopic systems: dynamical stabilisation in a finitely-rigid over-damped microscopic pendulum; deformability in red blood cells; and thermodynamic fluctuations in a system of hydrodynamically coupled colloidal particles. Each system is studied using optical tweezers. Part I provides an introduction to the development and operation of optical tweezers and gives an overview of the particle dynamics concepts that are built upon later in the thesis. Part II contains the work on dynamical stabilisation. The starting point for this work is the well-known Kapitza pendulum: a rigid pendulum whose suspension point is oscillated in such a way that the pendulum becomes stable in the upright position. Here I consider a pendulum that is finitely rigidity (i.e. a pendulum that is not mathematically infinitely rigid) and subjected to heavy damping. I present a model based on a scanning time-averaged ring-shaped optical trap in which a colloidal particle is trapped. The pendulum is localised by viscous fluid flow and oscillated by modulation of the ring-centre. A mathematical treatment of the model reveals a regime in which the pendulum explores different stability positions based on the modulation amplitude and frequency. These predictions are tested in simulations and experiments. In part III optical tweezers are used to stretch red blood cells (RBCs) in order to measure their deformability. The measured deformability of RBCs from patients suffering from diabetic retinopathy is measured and compared to the deformability of RBCs from healthy patients to investigate a link between DR and reduced RBC deformability. Finally, in part IV an investigation into the fluctuations of work applied to a hydrodynamically coupled system is presented. In a thermodynamically noisy system, the heat and work do not have exact values. Rather, they are represented by a probability distribution. Here, I present simulations and experiments that aim to measure the work distribution in a system consisting of two colloidal particles that are coupled by their aqueous environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available