Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M08: Steerable Particles II: New Ways to Manipulate Fluid-Mediated ForcesFocus Recordings Available
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Sponsoring Units: GSNP DSOFT DFD Chair: Ilona Kretzschmar, City College of New York Room: McCormick Place W-179B |
Wednesday, March 16, 2022 8:00AM - 8:36AM |
M08.00001: Statistical physics of feedback-based driven colloidal suspensions Invited Speaker: Yael Roichman When is it useful to stop a search process in its track, just to start all over again from the beginning? It turns out, that in very noisy processes in which the fluctuations in the time to reach a target are larger than its mean; this is often the case. A striking example of this phenomenon, is the fact that in some situations an enzyme should unbind its substrate to hasten a catalytic reaction. Other manifestations of expedited processes due to renewal and resetting appear naturally in many circumstances, such as in foraging animals, computer algorithms, and queuing theory. Diffusion with stochastic resetting serves as a paradigmatic model to study these phenomena, but the lack of a well-controlled platform by which this process can be studied experimentally has been a major impediment to research in the field. Here, we report the experimental realization of colloidal particle diffusion and resetting via holographic optical tweezers. We provide the first experimental corroboration of central theoretical results and go on to measure the energetic cost of resetting in steady-state and first-passage scenarios. In both cases, we show that this cost cannot be made arbitrarily small because of fundamental constraints on realistic resetting protocols. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M08.00002: Gravitational sedimentation of prolate particles with a non-uniform mass distribution Justin C Burton, Kavinda Nissanka, Xiaolei Ma The dynamics of sedimenting particles under gravity is surprisingly complex due to the presence of effective long-ranged forces. When the particles have a well-defined symmetry axis and non-uniform density, recent theoretical predictions suggest that prolate objects will repel and oblate ones will weakly attract. We tested these predictions using mass polar prolate spheroids, which are composed of 2 mm spheres glued together. We probe different aspect ratios (κ) and center of mass offsets (χ) by combining spheres of different densities. Experiments were done in both quasi-2D and 3D chambers. Three situations were explored: single particle flipping, repulsion between pairs of particles, and collections of hundreds of particles in 3D. Particles sediment at low Reynolds numbers and are tracked optically. Single particle trajectories are fit using a reduced mobility matrix model that can be solved analytically for the trajectory in time. Pairs of particles exhibit effective repulsion, and their separation roughly scales as ~(κ-1)/χ0.5, i.e. particles that are more prolate or have more mass asymmetry have stronger repulsion effects. In 3D, particles with χ>0 are distributed more uniformly than χ=0 particles, and the degree of uniformity increased with κ, indicating that the effective 2-body repulsion is manifested for a large number of particles. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M08.00003: Revealing the transverse diffusion of particles with different shapes in bed-load transport Fernando David Cúñez, Rachel Glade A fluid flow imposed over a granular bed can cause the grains to move by rolling, sliding, and jumping within a thin layer known as bed-load layer. In this layer, it may be observed a transverse diffusion and segregation of grains by size, which has been extensively studied, and shape, which has only recently been recognized as an important control. Here, we perform numerical simulations using an eulerian-lagrangian approach (CFD-DEM) to predict the intriguing behavior of grains present in the bed-load layer. We set a periodic channel filled with spherical and non-spherical particles, such as cubes and cylinders of equal mean diameter, sheared by a viscous Couette flow which imposes enough shear stress to move the particles by bed-load transport. We investigate the statistical properties of the transverse diffusion that non-spherical grains experience in the bed-load layer by tracking hundreds of individual trajectories throughout the entire bed, and the mechanisms involved that are mainly driven by the particles collisions and the fluid-grains interactions. These results illuminate the role of grain shape in controlling sediment diffusion, with implications for natural rivers, hillslopes, marine environments, and aeolian systems. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M08.00004: Hydrodynamically induced particle drift near corrugated surfaces Christina Kurzthaler, Danielle L. Chase, Howard A Stone We study the hydrodynamic interactions between sedimenting spheres and nearby corrugated surfaces, whose grooves are tilted with respect to the gravitational force. Our experiments show oscillatory particle trajectories with an overall drift along the sinusoidal surface corrugations, which agree quantitatively with our analytical perturbation theory. The theoretical predictions further reveal that the interactions of the flows induced by the particle motion with the surface shapes generate local pressure gradients, which explain the observed oscillatory dynamics. Additionally, we demonstrate that this behavior is generic for various surface shapes, including rectangular, sinusoidal, and triangular grooves. Finally, we theoretically and experimentally quantify the particle drift as a function of the shape and wavelength of the corrugations and the particle size to identify the parameters, which lead to an optimal transport of the particles. |
Wednesday, March 16, 2022 9:12AM - 9:24AM |
M08.00005: Tandem locomotion of droplets in a uniform electric field Petia Vlahovska, Chiara Sorgentone An isolated charge-neutral drop in a uniform electric field experiences no net force. However, a drop pair can move in response to mutual electrostatic (due to polarization) and hydrodynamic (due to the flow driven by surface electric stresses) interactions. If the droplets are identical, the center of mass of the pair remains fixed. However, if the droplets have different conductivity and/or permittivity, the pair experiences net motion. This droplet cooperative propulsion arises from the electrohydrodynamic flow and vanishes in perfect dielectric systems. We analyze the three-dimensional droplet trajectories using asymptotic theory and numerical simulations using the Boundary Integral Method. We find dynamics that can be quite intricate depending on the initial orientation of the droplets line-of-centers relative to the applied field direction. |
Wednesday, March 16, 2022 9:24AM - 9:36AM |
M08.00006: Synchronous oscillatory electro-inertial focusing for particle manipulation Gabriel Juarez, Giridar Vishwanathan The manipulation of suspended colloidal particles by external fields or hydrodynamic forces has applications ranging from cell sorting to water purification. Often, field methods such as electrophoresis are used for the precise manipulation of smaller particles (<1 um) while hydrodynamic methods based on fluid inertia such as inertial focusing are used for the rapid manipulation of relatively large particles (>10 um). Here, we present an experimental study on the non-linear coupling between electrophoretic and inertial forces for particle manipulation in microfluidic devices. This was realized by the application of an oscillatory electric field and a synchronous oscillatory flow at frequencies ranging from 10 to 1000 Hz. We investigated the effects of oscillatory amplitude, frequency, and phase difference between the electric and velocity fields on the rectified motion of colloidal particles. For certain combinations of oscillation frequencies and phase differences, we observed focusing positions and equilibrium states that were inexplicable by electrophoresis and inertial focusing alone. We demonstrate that this approach can overcome the limitations of a purely field-based or flow-based approach by manipulating nanoparticle suspensions at high-throughput. We hope to motivate the non-linear interaction between multiple synchronous oscillatory fields as a general strategy for particle control. |
Wednesday, March 16, 2022 9:36AM - 9:48AM |
M08.00007: High-throughput particle sorting and focusing using rectification of flow and forces Siddhansh Agarwal, Sascha Hilgenfeldt Inertial forces on fluid-borne objects arising due to nonlinear interactions of spatial flow gradients of a “fast" oscillatory flow are a powerful way to reliably and consistently steer particles in microfluidics, without the need for charges or chemistry. In many practical applications, the background oscillatory flow is driven by acoustically-excited bubbles, which typically simultaneously engender steady streaming and/or transport flows that deliver particles close to the bubble interface. While in earlier work we described previously unrecognized inertial forces due to the primary oscillatory driving in isolation, here we rigorously integrate these forces acting on particles in a realistic two dimensional bubble streaming flow. We account for streaming as well as for the presence of a nearby interface. A rigorous separation of time scales in two dimensions yields an overdamped system of equations for particle motion that is computationally efficient and accurately predicts particle displacements across streamlines in comparison to experiments. Our theory also suggests new particle manipulation strategies using oscillating bubbles as actuators of inertial forces, e.g., marker-less flow cytometry based on particle size or density, important for biomicrofluidics. |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M08.00008: Responsive colloidal molecules as reconfigurable microswimmers with programmable multistate dynamics Steven v Kesteren Contrary to their biological analogs or larger scale robotic systems, artificial microswimmers lack self-regulation and rely on external control to adapt their motion. Finding strategies to endow them with in-built feedback schemes, which couple particle properties to sensing and self-motility, remains an open challenge. Here, we realize active colloidal clusters with multi-state dynamics. These units are produced via capillary assembly [1] with fine geometrical control, comprising two different PNIPAM thermoresponsive microgels and a hard polystyrene colloid. The active clusters, actuated by AC electric fields, adapt their shape and dielectric properties via a temperature-induced transition upon illumination [2]. Different transition temperatures for the two microgels enable three distinct dynamical states via increasing-intensity light inputs. The sequential reconfiguration of the microgels affects the chirality and persistence of the trajectories, connecting active dynamics to the design of different particle states with tailored adaptive pathways. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M08.00009: Transport and Assembly of Colloidal Nanoparticles by a Moving Phase Boundary Tom Shneer, Linda S Hirst, Alauna Wheeler, Timothy J Atherton We consider the implications of a general continuum model of a colloidal nanoparticle and liquid crystal solvent system. This model suggests that a moving liquid crystal phase boundary can transport colloidal nanoparticles and contribute to their aggregation as the boundary shape-shifts to minimize the free energy of the system. We discuss how the inclusion of colloidal nanoparticles might change the dynamics of the liquid crystal solvent. Lastly, we show how a simple analysis of this model may imply that there are characteristic timescales which depend on general system parameters. This model might assist in the discovery of self-assembled microscale materials with applications in medicine, cosmetics, and food science. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M08.00010: Breaking Stokes' reversibility through nonlinear hydrodynamic interactions Haim Diamant, Yulia Sokolov When well-separated rigid objects in a viscous fluid are subjected to an alternating drive, their net translation vanishes due to Stokes' reversibility. We study the breaking of reversibility through nonlinear hydrodynamic interactions, brought about by an intrinsic response of the objects to the drive. The responsiveness may arise, for example, from changes in the objects' shapes or their positions in an external potential. This nonlinear effect may be used to concentrate or disperse an assembly of particles in the limit of zero Reynolds number using an alternating drive. We demonstrate it in a simple simulation of forced flexible objects. |
Wednesday, March 16, 2022 10:24AM - 10:36AM |
M08.00011: Statistical analysis of freezing stages in supercooled water microdroplets Claudiu A Stan, Armin Kalita, Maximillian Mrozek-McCourt, Thomas F Kaldawi, Matias Daniel de Almeida, Philip R Willmott, Raymond G Sierra, Ne-Te Duane Loh, Hartawan Laksmono, Jason E Koglin, Matt J Hayes, Rob Paul, Serge A. H Guillet, Mengning Liang, Andrew L Aquila, Sebastien Boutet The details of solidification in metastable liquids remain relatively unexplored. An important example is the freezing of supercooled water microdroplets, which is relevant to atmospheric processes. We investigated freezing in 40 µm water droplets that were supercooled by evaporation in a vacuum chamber, a process that has many similarities to the freezing of water in clouds. Individual droplets froze after different times of flight due to the randomness of ice nucleation. A large number of drops were imaged optically to capture the dendritic growth of ice crystals and subsequent solidification processes up to the cracking and shattering of drops. More than ten thousand droplet images, recorded at several times of flight, were analyzed and classified into image types that correspond to different stages of freezing. As the time of flight increased, the distribution of image types evolved from primarily liquid drops to primarily shattered drops. Despite a substantial broadening caused by ice nucleation statistics, the change in distributions with time could be used to determine the temporal order of freezing stages and their approximate duration. The homogeneous ice nucleation rate was estimated and found to be consistent with previous measurements. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M08.00012: Evidence for higher-order phase transitions in the two-dimensional Ising model Kedkanok Sitarachu, Michael Bachmann We employed the microcanonical inflection-point analysis method [1], which was introduced to identify and classify phase transitions in systems of any size, to study the 2D Ising model at various lattice sizes and in the thermodynamic limit [2]. Exact results for the density of states, obtained by algorithmic computation [3,4], provide evidence for higher-order transitions in addition to the well-studied second-order ferromagnetic-paramagnetic phase transition. An independent third-order phase transition is identified in the ferromagnetic phase, whereas another third-order transition resides in the paramagnetic phase. The latter is a dependent transition, i.e., it is inevitably associated with the critical transition. Detailed cluster analysis is performed to study the nature of the dependent transition, which can be interpreted as a precursor of the ferromagnetic-paramagnetic phase transition in the disordered phase. It is noteworthy that both higher-order transitions survive in the thermodynamic limit. |
Wednesday, March 16, 2022 10:48AM - 11:00AM |
M08.00013: Limit shape phase transitions. A merger of Arctic circles. Alexandre G Abanov, Dimitri M Gangardt, James S Pallister A limit shape phenomenon in statistical mechanics is the appearance of a most probable macroscopic state. This state is usually characterized by a well-defined boundary separating frozen and liquid spatial regions. The earliest studies related to this phenomenon in the context of crystal shapes are in works by Pokrovsky and Talapov [1]. We consider a class of topological phase transitions in the limit shape problem of statistical mechanics. The problem considered is generally known as the Arctic circle problem. The considered phase transition can be visualized as the merging of two melted regions (Arctic circles). We establish the mapping, which identifies the transition as the transition known in lattice QCD and random matrix problems [2,3]. The transition is a continuous phase transition of the third order. We identify universal features of the limiting shape close to the transition using the hydrodynamic description. |
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