Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K08: Steerable Particles I: New Ways to Manipulate Fluid-Mediated ForcesFocus Recordings Available
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Sponsoring Units: GSNP Chair: Yael Roichman, Tel Aviv University Room: McCormick Place W-179B |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K08.00001: Active Janus and Patchy Particles Near Boundaries Invited Speaker: Ilona Kretzschmar Janus particles, i.e., particles with two distinct halves, have been heralded as new materials for assembly, drug deliver, autonomous motion, and emulsion stabilization since deGennes’ 1991 Nobel lecture. Janus particles, i.e., particles with a 50% surface coating, are a specific subset of patchy particles that can have any number of material patches on their surface. Our laboratory has spent the past 17 years developing methods to make a versatile set of Janus and patchy particles with magnetic, photonic, and catalytic properties and studying the behavior of such particles in electric and magnetic fields as well as at and near boundaries. In this talk, our research contributing to understanding the behavior of such particles in the vicinity of solid/liquid, liquid/liquid, and air/liquid interfaces will be discussed. The talk will discuss various swimming mechanisms and then focus more closely on self-diffusiophoresis exhibited by systems with Pt-catalyzed H2O2 decomposition. Specifically, probing the impact of activity on the Janus/patchy particle/boundary interaction will be highlighted. Support for this work has been provided by the National Science Foundation CBET, HRD, and DMR as well as the Air Force Office of Scientific Research. |
Tuesday, March 15, 2022 3:36PM - 3:48PM |
K08.00002: Complex behaviors of colloidal particles under a one-dimensional solute concentration gradient: Unravelling three-dimensional information from one-dimensional experiments Suin Shim, Ankur Gupta, Benjamin M Alessio, Guang Chen, Janine Nunes, Howard A Stone We investigate diffusiophoresis of polystyrene particles under a one-dimensional electrolyte concentration gradient. Even though the salt concentration field is set up in a relatively simple configuration, the response of particles to the solute distribution is governed by a variety of factors, such as the particle surface-electrolyte interaction and particle sizes, as well as the surface properties and shape of the microfluidic channel. We use a dead-end pore geometry to show, both experimentally and theoretically, different behaviors of charged particles that can emerge through a one-dimensional solute concentration gradient and the influence of pore dimensions, pH, and surface properties of particles and channel. |
Tuesday, March 15, 2022 3:48PM - 4:00PM |
K08.00003: Steering Colloids using Chemical Gradients Mark N McDonald, Cameron K Peterson, Douglas R Tree Dynamically programmable colloidal materials (DPCMs) are an emerging class of materials that change their structure based on external stimuli. With the correct programming, DPCMs could be influenced to self-assemble into arbitrary structures currently unattainable, with applications in photonics, tissue engineering, and nanorobotics. However, realizing such applications requires spatiotemporal control of colloids to a combined precision and scale that is currently unattainable. Inspired by the complex systems of feedback control and non-equilibrium chemical signals in biological systems, it has been suggested that colloidal particles can be controlled using internal chemical feedback loops. By combining this idea of chemical feedback with previous microfluidics research that steers colloidal particles with an electric field, we have devised a new method of steering colloidal particles using externally applied chemical gradients. This is intended as a stepping-off point for future systems that assemble using internal feedback. Our simulations use model predictive control to steer colloidal particles on various trajectories using a chemical solute gradient. We have also derived design rules that illustrate the constraints on controlling colloidal particles using chemical gradients. |
Tuesday, March 15, 2022 4:00PM - 4:12PM |
K08.00004: Diffusiophoresis in Zwitterionic Gradients Parth Shah, Rodrigo N Azevedo, Nan Shih, Todd M Squires Diffusiophoresis (DP) has seen increasing attention for its ability to control and manipulate suspended objects using external solute gradients. While most work has focused on DP under electrolyte gradients, different types of solutes have seen much less attention. Here we present theoretical and experimental studies of particle DP under gradients of zwitterions, i.e., electrical dipoles. We develop a theory for zwitterion DP that predicts that colloids will always migrate up zwitterion gradients, but with velocities that scale linearly with the concentration gradient, in contrast to the logarithmic gradient scaling of conventional electrolyte DP. Moreover, DP mobilities scale with the square of the zwitterion dipole moment – which depends on the distance between the charged ends of the molecule. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K08.00005: Dynamical control of light steering with magneto-photonic metaparticles Ognjen Ilic The ability to deliver light of desired properties (wavelength, polarization, etc.) to any target spot in a medium has broad relevance for applications in biology, biomedicine, nano-chemistry, and radiation therapy. It is often desirable that such delivery is adaptively controlled with a non-invasive mechanism, that it exhibits significant selectivity for desired light properties, and that it does not require direct line-of-sight access to the target spot. We approach this challenge by introducing a meta-particle concept that integrates magnetic and photonic functionalities. Here, the surface of the meta-particle is endowed with light steering capability from embedded nano-photonic elements. Simultaneously, the particle incorporates anisotropic magnetic features to control its orientation with an external magnetic field. We present theoretical and experimental results that show proof of concept large-angle steering of light, as well as the capability to orient and actuate multiple particles at once. The fabrication process combines nano-imprint lithography and photolithography and is highly scalable. Finally, we discuss the potential for the photonic and the magnetic functionality of the particle to be designed largely independently of each other, therefore offering access to the complete toolbox of nanophotonics for realizing sophisticated flows of light. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K08.00006: Light-Driven Motion of Non-Porous SiO2 Particles in the Vicinity of Microgels Anjali Sharma Light triggered size response of microgels in the presence of a photo-sensitive surfactant generates a local fluid flow in the vicinity of microgels causing tracer particles (non-porous SiO2) to drift away radially, on illumination with light. The extent and duration of this repulsion is manipulated by varying the wavelength of light. This motion stems from diffuso-osmotic flows created by the constant influx and expulsion of the photo-sensitive azobenzene containing surfactant molecules through the matrix of the microgel enabling it to act like a surfactant pump, which on appropriate illumination is capable of generating a stable, steady and continuous flow. |
Tuesday, March 15, 2022 4:36PM - 4:48PM |
K08.00007: Enhanced colloidal particle trapping in microgrooved channels via diffusiophoresis Guido Bolognesi, Naval Singh, Goran Vladisavljevic, Francois Nadal, Cecile Cottin-Bizonne, Christophe Pirat The controlled transport of sub-micron colloidal particles within a confined environment, such as a porous medium or a dead-end channel, is a key feature in several technological applications (e.g., drug delivery, diagnostics) as well as in living systems (e.g., mass transport in tissues and capillaries). |
Tuesday, March 15, 2022 4:48PM - 5:00PM Withdrawn |
K08.00008: Dynamics of nanoparticle self-assembly by liquid crystal sorting Orlando Guzman, Gael Segura, Erick Serrato, Emmanuel Flores We model the rapid segregation of nanoparticles away from nematic domains, which has been observed experimentally in a suspension of gold nanoparticles in 5CB below the isotropic-nematic transition temperature, using nonlinear dynamical equations that couple nanoparticle concentration and liquid crystal order parameter. We contrast the behaviors obtained when the LC order parameter is treated as a scalar or a tensor, as well as the different rates of evolution observed with each of these. We find an initial linear regime where the ordering of the nematic phase proceeds exponentially with time and, after a lag period, a second regime where the onset of nonlinear dynamics leads to nanoparticle segregation to locally isotropic regions and saturation of the order parameter. The choice of a scalar or tensor LC order parameter does not change this sequence but results in a clear overshooting of the nonlinear saturation level for the tensor order parameter case. These results are found to be insensitive to weak anchoring due to coupling of gradients of the conserved and non-conserved variables. Our modeling approach can be extended from instantaneous quenches to cases where the cooling rate is finite and to other systems where a locally conserved concentration is coupled to a orientation field. |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K08.00009: Focusing and Sorting Polystyrene Particles and Liposomes via Diffusiophoresis in Straight Flat Microchannels Guido Bolognesi, Goran Vladisavljevic, Naval Singh, Christophe Pirat, Cecile Cottin-Bizonne, Francois Nadal, Adnan Chakra We report a novel phenomenon that enables the pre-concentration and sorting of charged polystyrene particles and liposomes dispersed in a continuous flow within a straight flat microchannel. A 3-inlet junction microfluidic device is used to generate a steady-state salt concentration gradient in the direction perpendicular to the flow. As a result, particles dispersed in the electrolyte solution accumulate into two symmetric regions of the channel by forming two distinct focusing spots. Despite a similar colloid behaviour being reported in previous studies with a similar flow configuration, our numerical and experimental analysis show that the observed particle dynamics is driven by a novel unreported physical mechanism, that combines diffusiophoresis, diffusioosmosis and hydrodynamic effects. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K08.00010: Sperm chemotaxis in marine species is optimal at physiological flow rates according theory of filament surfing Benjamin M Friedrich, Steffen Lange Sperm of marine invertebrates have to find eggs cells in the ocean. Turbulent flows mix sperm and egg cells up to the millimeter scale; below this, active swimming and chemotaxis become important. Previous work addressed either turbulent mixing or chemotaxis in still water. Here, we present a general theory of sperm chemotaxis inside the smallest eddies of turbulent flow, where signaling molecules released by egg cells are spread into thin concentration filaments. Sperm cells 'surf' along these filaments towards the egg. External flows make filaments longer, but also thinner. These opposing effects set an optimal flow strength. The optimum predicted by our theory matches flow measurements in shallow coastal waters. Our theory quantitatively agrees with two previous fertilization experiments in Taylor-Couette chambers and provides a mechanistic understanding of these early experiments. 'Surfing along concentration filaments' could be a paradigm for navigation in complex environments in the presence of turbulent flow. |
Tuesday, March 15, 2022 5:24PM - 5:36PM |
K08.00011: Thermal Fluctuations of Singular Bar-Joint Mechanisms Manu Mannattil, Jennifer M Schwarz, Christian D Santangelo A bar-joint mechanism is an assembly of joints connected by bars that can deform and alter its shape without changing the bar lengths. DNA origami has enabled the fabrication of such mechanisms at the nanoscale, where thermal fluctuations cannot be neglected. Here we develop a general formalism to study the consequences of equilibrating such mechanisms with a thermal bath. A meaningful description of the free-energy landscape of a mechanism is in terms of its shape coordinates that parameterize its shape space, i.e., the set of all its lowest-energy configurations with distinct shapes. Shape spaces of bar-joint mechanisms are often characterized by singularities due to states of self stress -- equilibrium configurations capable of supporting nonzero tensions in the bars. We show that in the presence of such singularities, the landscape is dominated by their neighborhoods. We successfully apply our formalism to understand the free-energy landscape of the four-bar linkage, which is the canonical example of a mechanism with shape-space singularities, as well as larger mechanisms like a triangulated origami. For these two mechanisms, the free-energy landscape suggests that configurations closer to the singularity are more likely to be found than others. |
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