Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session ZC34: Micro/Nano scale Flows: Particles |
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Chair: William Uspal, University of Hawai'i at Manoa Room: 201 |
Tuesday, November 21, 2023 12:50PM - 1:03PM |
ZC34.00001: Anomalous Dependence on Fuel Concentration for the Dynamics of Catalytic Microswimmers near Obstacles William E Uspal, Carolina van Baalen, Mihail N Popescu, Lucio Isa Efficient exploration of space is a paramount motive for active colloids in practical applications. On the other hand, introducing activity may lead to surface-bound states, posing an impediment to efficient spatial exploration. Here, we study how the interplay between self-propulsion and fuel-dependent affinity for surfaces affects the efficiency of a catalytically-active microswimmer for exploration of an interface decorated with obstacles. In a regime of constant propulsion velocity as a function of fuel concentration, we find that microswimmer-obstacle interactions strongly depend on fuel concentration, leading to a counter-intuitive decrease in exploration efficiency with an increase in available fuel. Additionally, under some conditions, the affinity of a swimmer for obstacles can change significantly over time. Using experiments and theoretical predictions, we show that these largely overlooked phenomena are most likely the result of a change in the surface properties of the microswimmer's catalytic face when exposed to H2O2. Our findings provide far-reaching insights regarding the interpretation of experimental studies of active colloids, as well as new means of controlling their dynamics in complex environments |
Tuesday, November 21, 2023 1:03PM - 1:16PM |
ZC34.00002: Elastohydrodynamic collision of wet particles SOURADEEP ROYCHOWDHURY, ROBERT H DAVIS The dynamics of small elastic particles coated with thin liquid layers has many applications in the chemical and pharmaceutical industries, including wet granular flows, dispersion filtering, particle agglomeration, slurry transport, spray coating, and pneumatic transport. Here, we extend the hard-sphere model of Davis & Sitison, Phys. Rev. Fluid. 2020, to a soft-sphere model with dynamic particle deformation. We combine lubrication theory and Hertz contact theory of linear elasticity to model the elastohydrodynamic deformation during a collision of two wet spheres. The problem is governed by an interplay between the Stokes number, elasticity parameter, and dimensionless thickness of the fluid film, which determine whether or not the particles will rebound after collision. We develop an asymptotic theory for head-on collisions in the regime of small deformations. For larger deformations (i.e., comparable to the gap size), the pressure due to squeezing lubrication in the fluid-filled gap between the particles leads to elastic deformation, which allows the particles to rebound without touching each other. Particle deformation causes a decrease in relative velocity during the approaching phase, resulting in longer collision times. For small particle inertia, agglomeration occurs, while for small elasticity numbers, the hard-sphere limit is approached. |
Tuesday, November 21, 2023 1:16PM - 1:29PM |
ZC34.00003: Purcell's elastic swimmer: Drift of elastic hinges in oscillatory shear flows James Roggeveen, Howard A Stone In low-Reynolds-number flows, time reversibility makes it challenging for particles and organisms to sustain locomotion without the presence of an external force. For example, Purcell demonstrated that simply opening and closing a hinge, which is a successful form of locomotion in fluids at high Reynolds numbers, leads to no net motion of the object under the Stokes flow approximation. Nature has found ways to avoid this constraint such as by using wave-like motions of elastic filaments that are driven by the organism itself. In terms of passive particles, the authors have recently shown that it is possible to enable passive motion across streamlines, i.e., a steady drift, of a rigid slender particle in a steady shear flow if the particle is suitably asymmetric. In this work, we extend these ideas to consider the motions of a symmetrically bent slender filament when it is allowed to operate like a linearly elastic hinge. We consider the case where such a particle is placed into a flow with a sinusoidally varying shear rate, resulting in no net displacement of the fluid packets. We show that by simply adding one degree of elastic freedom to the symmetric hinge-shaped body that the particle will experience a net drift even as the fluid remains stationary on average. |
Tuesday, November 21, 2023 1:29PM - 1:42PM |
ZC34.00004: Slow reorientation dynamics of symmetry-breaking self-propelling motion Gunnar G Peng An isotropic diffusiophoretic active particle that emits a chemical and interacts with it to drive flow is an example of an object that can exhibit symmetry-breaking spontaneous motion in an arbitrary direction, essentially due to being repelled by its own chemical wake. We analyse how this self-propulsion is affected by weak perturbations, such as a small applied force or background chemical gradient (which could be due to the presence of other particles). The arbitrariness of the self-propulsion direction allows it to be slowly reoriented by the weak perturbation over a long timescale. By expanding to linear order in the perturbation amplitude and imposing a solubility condition, we derive the resulting reduced dynamics for the direction of the velocity vector, including a numerically calculated coefficient that depends on the parameters of the problem. We argue that the same form of result would be obtained generically for many different cases of weakly perturbed symmetry-breaking motion. |
Tuesday, November 21, 2023 1:42PM - 1:55PM |
ZC34.00005: Predicting the particle size distribution of silver nanoparticles: coupled PBM-CFD simulations and experimental study Konstantia Nathanael, Paula Pico, Alessio D Lavino, Nina Kovalchuk, Mark J Simmons, Omar K Matar Extensive experimental and computational work has been performed over the last decades to elucidate the effect of different chemical reagents and reaction operating conditions on the properties of silver nanoparticles (AgNPs) for different applications. However, despite all these efforts, it is still very challenging to predict the final properties of AgNPs. |
Tuesday, November 21, 2023 1:55PM - 2:08PM |
ZC34.00006: Attracting modes of sedimentation for highly elastic fibers settling under gravity in a viscous fluid Yevgen Melikhov, Maria L Ekiel-Jeżewska The sedimentation of highly elastic fibers under gravity in a viscous fluid is investigated numerically. The fiber is represented by an almost inextensible bead-spring chain with a small bending stiffness. The fiber’s flexibility is described by a dimensionless elasto-gravitation number B which relates hydrodynamic forces acting on the fiber and the fiber’s bending stiffness. Sedimentation dynamics are obtained employing the Hydromultipole numerical codes to solve the Stokes equations via a very accurate multipole method. The evolution of the fiber is monitored over a relatively long time. In addition to the fixed shape modes previously identified and discussed in the literature, we find attracting sedimentation modes with periodically changing shapes. A brief analysis of the characteristic features of all these sedimentation modes is presented. Each mode is found only in a certain range of values of the fiber’s aspect ratio N and its elasto-gravitation number B, as shown in a 'phase diagram' of the modes. Our results demonstrate that the dynamics of highly elastic fibers are sensitive not only to B, but also to N. |
Tuesday, November 21, 2023 2:08PM - 2:21PM |
ZC34.00007: Reaction-mediated phoretic transport of colloids in microfluidic channels Haoyu Liu, Mobin Alipour, Amir Pahlavan Reactive flows are ubiquitous in many natural phenomena and technological applications, from cargo transport in cells to alkaline vents at the bottom of oceans. Chemical reactions can generate and sustain chemical gradients, which in turn can lead to diffusiophoretic migration of colloids. Here, we report on how the interplay between flow and reaction-mediated chemical gradients shape colloidal migration patterns using experiments and numerical simulations. |
Tuesday, November 21, 2023 2:21PM - 2:34PM |
ZC34.00008: Viscous tweezers: controlling particles with viscosity Tali Khain, Michel Fruchart, Vincenzo Vitelli Control of particle motion is generally achieved by applying an external field that acts directly on each particle. In this talk, we propose a global way to manipulate the motion of a particle by dynamically changing the properties of the fluid in which it is immersed. We exemplify this principle by considering a small particle sinking in an anisotropic fluid whose viscosity depends on the shear axis. In the Stokes regime, the motion of an immersed object is fully determined by the viscosity of the fluid through the mobility matrix, which we explicitly compute for a pushpin-shaped particle. Rather than falling upright under the force of gravity, as in an isotropic fluid, the pushpin tilts to the side, sedimenting at an angle determined by the viscosity anisotropy axis. By changing this axis, we demonstrate control over the pushpin orientation as it sinks, even in the presence of noise, using a closed feedback loop. This strategy to control particle motion, that we dub viscous tweezers, could be experimentally realized in a fluid comprised of elongated molecules by suitably changing their global orientation. |
Tuesday, November 21, 2023 2:34PM - 2:47PM |
ZC34.00009: Sedimentation of spheroids in Newtonian fluids with spatially varying viscosity Vishal Anand, Vivek Narsimhan This paper examines the rigid body motion of a spheroid sedimenting in a Newtonian fluid with a specified, spatially-varying viscosity field. We leverage the arguments of symmetry to find the general expression for the particle’s mobility tensor relating the external force and torque with the spheroid's velocity and rotation rate. We find that a constant viscosity gradient does not alter force/velocity and torque/rotation couplings; however, the force/rotation and torque/velocity couplings are altered. Illustrative examples obtained via reciprocal theorem based estimation of the mobility tensor show that the sedimenting spheroid exhibits a multitude of different behaviors ranging from tumbling to stable orientations, based on the shape of the particle(aspect ratio) and the direction of the viscosity gradient. These results are markedly different from the case when the fluid has spatially uniform viscosity and the spheroid sediments with a constant initial orientation. |
Tuesday, November 21, 2023 2:47PM - 3:00PM Author not Attending |
ZC34.00010: Abstract Withdrawn |
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