Browsing by Author "Kuei, Steve"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Coiling of semiflexible paramagnetic colloidal chains
    (Royal Society of Chemistry, 2023) Spatafora-Salazar, Aldo; Kuei, Steve; Cunha, Lucas H.P.; Biswal, Sibani Lisa
    Semiflexible filaments deform into a variety of configurations that dictate different phenomena manifesting at low Reynolds number. Harnessing the elasticity of these filaments to perform transport-related processes at the microfluidic scale requires structures that can be directly manipulated to attain controllable geometric features during their deformation. The configuration of semiflexible chains assembled from paramagnetic colloids can be readily controlled upon the application of external time-varying magnetic fields. In circularly rotating magnetic fields, these chains undergo coiling dynamics in which their ends close into loops that wrap inward, analogous to the curling of long nylon filaments under shear. The coiling is promising for the precise loading and targeted transport of small materials, however effective implementation requires an understanding of the role that field parameters and chain properties play on the coiling features. Here, we investigate the formation of coils in semiflexible paramagnetic chains using numerical simulations. We demonstrate that the size and shape of the initial coils are governed by the Mason and elastoviscous numbers, related to the field parameters and the chain bending stiffness. The size of the initial coil follows a nonmonotonic behavior with Mason number from which two regions are identified: (1) an elasticity-dependent nonlinear regime in which the coil size decreases with increasing field strength and for which loop shape tends to be circular, and (2) an elasticity-independent linear regime where the size increases with field strength and the shape become more elliptical. From the time scales associated to these regimes, we identify distinct coiling mechanisms for each case that relate the coiling dynamics to two other configurational dynamics of paramagnetic chains: wagging and folding behaviors.
  • Thumbnail Image
    Item
    Dynamics of semiflexible paramagnetic colloidal chains under a rotational magnetic field
    (2019-04-12) Kuei, Steve; Biswal, Lisa
    The rich dynamics of stiff and flexible filaments in flow and their propensity for non-reciprocal orbits is relevant for both naturally occurring and industrially relevant phenomena, such as flagellar motion and polymer processing, as well as for developing applications, such as microfluidic scale propulsion and fluid manipulation. However, the connection between a filament’s elastic properties, the external driving forces, and its resulting dynamics is not well understood; in particular, both computational and theoretical results indicate that the scaling behaviors of fibers in the intermediate semiflexible regime deviate from the results expected from rigid and flexible fibers. We synthesize paramagnetic colloidal particle chains, and then utilize a rotating magnetic field as an external force, with which we are able to experimentally identify and probe various dynamical regimes. By complementing our studies with Brownian dynamics simulations of a bead-spring chain as well as theoretical arguments, we find that the dynamics of the system depend on the dimensionless Mason and magnetoelastic numbers, and use them to elucidate, predict, and optimize fiber dynamics.
  • Thumbnail Image
    Item
    From strings to coils: Rotational dynamics of DNA-linked colloidal chains
    (American Physical Society, 2017) Kuei, Steve; Garza, Burke; Biswal, Sibani Lisa
    We investigate the dynamical behavior of deformable filaments experimentally using a tunable model system consisting of linked paramagnetic colloidal particles, where the persistence length lp, the contour length lc, and the strength and frequency of the external driving force are controlled. We find that upon forcing by an external magnetic field, a variety of structural and conformational regimes exist. Depending on the competition of forces and torques on the chain, we see classic rigid rotator behavior, as well as dynamically rich wagging, coiling, and folding behavior. Through a combination of experiments, computational models, and theoretical calculations, we are able to observe, classify, and predict these dynamics as a function of the dimensionless Mason and magnetoelastic numbers.
  • Thumbnail Image
    Item
    Interfacial energetics of two-dimensional colloidal clusters generated with a tunable anharmonic interaction potential
    (American Physical Society, 2018) Hilou, Elaa; Du, Di; Kuei, Steve; Biswal, Sibani Lisa
    Interfacial characteristics are critical to various properties of two-dimensional (2D) materials such as band alignment at a heterojunction and nucleation kinetics in a 2D crystal. Despite the desire to harness these enhanced interfacial properties for engineering new materials, unexpected phase transitions and defects, unique to the 2D morphology, have left a number of open questions. In particular, the effects of configurational anisotropy, which are difficult to isolate experimentally, and their influence on interfacial properties are not well understood. In this work, we begin to probe this structure-thermodynamic relationship, using a rotating magnetic field to generate an anharmonic interaction potential in a 2D system of paramagnetic particles. At low magnetic field strengths, weakly interacting colloidal particles form non-close-packed, fluidlike droplets, whereas, at higher field strengths, crystallites with hexagonal ordering are observed. We examine spatial and interfacial properties of these 2D colloidal clusters by measuring the local bond orientation order parameter and interfacial stiffness as a function of the interaction strength. To our knowledge, this is the first study to measure the tunable interfacial stiffness of a 2D colloidal cluster by controlling particle interactions using external fields.