Browsing by Author "Zhao, Jingjing"

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    Characterizing Nonlinear Dynamics with Stochasticity Using Semiflexible Paramagnetic Colloidal Filaments
    (2019-04-19) Zhao, Jingjing; Biswal, Sibani Lisa
    Elastic Brownian filaments exhibit rich dynamics that are essential in numerous biological and industrial processes, such as intracellular transport and flagellar motion in biology, processing of rod-like polymers, and other rheological phenomena found in soft matter systems. Single filament scale research is needed to better understand these dynamics. One common theme governing these systems is non-linear dynamics as a result of the competition between the elastic and viscous forces acting on the filament, with thermal energy oftentimes adding stochasticity to the dynamics. This has resulted in behavior that cannot be simply explained by mechanical force balances. In this work, we investigate the two-dimensional dynamics of a semiflexible filament on the low-Reynolds number regime using experimental, theoretical and numerical methods. Experimentally, we synthesize DNA-linked superparamagnetic colloidal filaments and apply them as models for inextensible semiflexible filaments under various external fields. Theoretically, we utilize a worm-like chain model and slender-body theory to provide scaling and other analytical insights. A bead-spring chain model Brownian dynamics simulation is utilized to provide a numerical approach to support the experimental and theoretical results. Applying these methods, we study the model filament dynamics induced by two force fields: magnetic and gravitational fields. Firstly, the filament is induced to bend and buckle using an orthogonal magnetic field. The limits of linear elastic bending observed within an experimental regime is identified. Various non-linear dynamical stages leading to a higher-order filament buckling and configurational instabilities are examined. The inhomogeneous temporal evolution of the buckling wavelength is analyzed and the contractions under various conditions are compared. Secondly, a gravitational field is applied to semiflexible filaments. The configurational transitions and sediment dynamics of the model filament is studied in an otherwise quiescent fluid. The effect of thermal fluctuations on the stochasticity of the filament configurations and orientations is investigated. We also consider the settling dynamics of the semiflexible filament in more confined geometries, such as a post array, where interactions between the filament and post influence the migration path. This thesis advances our understanding of the multitude of configurations and non-linear dynamics of semiflexible colloidal filaments induced by external forces and under the influence of thermal fluctuations. This body of work will contribute to the development of novel soft materials as well as providing new insights of the properties of related filament systems.
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    Nonlinear multimode buckling dynamics examined with semiflexible paramagnetic filaments
    (American Physical Society, 2018) Zhao, Jingjing; Du, Di; Biswal, Sibani Lisa
    We present the contractile buckling dynamics of superparamagnetic filaments using experimental, theoretical, and simulation approaches. Under the influence of an orthogonal magnetic field, flexible magnetic filaments exhibit higher-order buckling dynamics that can be identified as occurring in three stages: initiation, development, and decay. Unlike initiation and decay stages where the balance between magnetic interactions and elastic forces is dominant, in the development stage, the influence of hydrodynamic drag results in transient buckling dynamics that is nonlinear along the filament contour. The inhomogeneous temporal evolution of the buckling wavelength is analyzed and the contractions under various conditions are compared.
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    Settling dynamics of Brownian chains in viscous fluids
    (American Physical Society, 2022) Cunha, Lucas H.P.; Zhao, Jingjing; MacKintosh, Fred C.; Biswal, Sibani Lisa; Center for Theoretical Biological Physics
    We investigate the dynamics of sedimenting Brownian filaments using experimental, computational, and theoretical approaches. The filaments under consideration are composed of linked colloidal particles that form bead-spring-like chains. Under the action of gravitational forces, the nonlocal hydrodynamic interactions cause the filaments to bend and rotate to get their end-to-end direction perpendicular to gravity. Different reorientation mechanisms are verified for different regimes of flexibility, characterized by the elastogravitational number. The thermal forces promote shape and orientation fluctuations around the steady configurations of the reciprocal non-Brownian chains. The competition between the reorientation mechanisms and the Brownian effects results in normal distributions of the orientation of the chains. In the stiff regime, these fluctuations cause the chains to fall faster than their reciprocal non-Brownian cases. With increasing flexibility, thermal fluctuations lead to more compact configurations of the chains and higher average settling velocity. Nonetheless, chain flexibility plays an important role on lateral migration. The interplay between elastic, gravitational, and thermal forces leads to important secondary influences on the filament settling dynamics.