Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session J18: Microscale and Nanoscale Flows: Electrokinetics |
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Chair: Siamak Mirfendereski, University of Colorado Boulder Room: 250 B |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J18.00001: Particle-Level simulations using diffusiophoresis and cellular automata to create dynamic Turing patterns Siamak Mirfendereski, Ethan J Coleman, Ankur Gupta Turing patterns, emerging from short-range activation and long-range inhibition in reaction-diffusion systems, are commonly observed in biological systems. Recent research has shown that incorporating diffusiophoretic transport can enhance Turing theory, enabling a degree of control that allows for robust modeling of biological patterns. However, such chemical-mechanical mechanisms usually yield static structures, failing to capture the dynamic behaviors typical of biological systems. Cellular automata, on the other hand, are dynamic discrete models capable of reproducing complex evolutionary and growth-like behaviors given an initial state. Traditionally, these two classes of models have been treated separately. Here, we introduce a novel framework where the cells migrate through diffusiophoresis, in response to the biomolecular signals, and then evolve via cellular automata. Our large-scale Eulerian-Lagrangian simulations reveal that this unified framework generates intriguing evolving structures, whose characteristics are controllable by both the reaction-diffusion model and cellular automata principles. Additionally, we quantify how cell concentration and size limitations impact pattern formation and its subsequent evolution. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J18.00002: Steering Copper Dendrites with Localized Magnetohydrodynamic Convection Jacob M Neal, Thomas Underwood Copper dendrite growth in electrochemical cells with CuSO4 electrolyte and copper electrodes involves complex fluid-structure interactions and magnetohydrodynamics. This study focuses on the localized fluid mechanics at the dendrite tips, examining how coupled fluid flow and moving dendrites' boundaries influence each other. The growth process is governed by the interplay between ionic diffusion, electrochemical reaction rates, and fluid flow, with the dendrite tips experiencing enhanced mass transfer due to localized convection. When an external magnetic field is applied, Lorentz forces induce secondary flows, modifying the shear stress and mass transfer rates at the dendrite tips. Experiments reveal that without a magnetic field the dominant branched structures grow parallel to the current density field. In contrast, the presence of a magnetic field can destabilize these structures by inducing a crossflow and bending the branches, leading to more chaotic growth. The magnetic field can suppress or enhance dendrite growth depending on the working current density, while at high current densities the dendrite forest is chaotically broken with stochastic healing and re-breaking dynamics. This research provides insights into controlling dendrite growth in electrochemical systems, with implications for improving battery performance and preventing short circuits, or increasing electrodeposition for species extraction from aqueous electrolyte solutions. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J18.00003: Strong thermoelectric response of weak electrolytes Rajkumar Sarma, Steffen Hardt Recently, there has been increasing attention to materials that yield large thermoelectric responses. We have analyzed the potential of weak electrolytes for thermoelectric energy conversion. Weak electrolytes only partially dissociate into ions when dissolved. For these electrolytes, the equilibrium between the dissociated and the charge-neutral solute is defined by the dissociation constant. The dissociation constant depends on the temperature of the electrolyte solution. We have computed the thermovoltage generated when a nanochannel is filled with a weak electrolyte and subjected to different temperatures at each end. When the EDLs of two opposing channel walls overlap, the channel is mainly filled with counterions. A counterion concentration gradient forms along the channel, which is caused by the temperature-dependent partial dissociation of ions. This concentration gradient drives an electric current. We have modified the Nernst-Planck equation to take partial ion dissociation into account and numerically solved it along with the Poisson and heat transport equations. The results show that, for the same degree of EDL overlap, a thermal voltage is achieved with weak electrolytes that can be 3.5 times higher than for fully dissociated electrolytes. This makes confined solutions of weak electrolytes promising candidates for thermoelectric energy conversion. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J18.00004: Resonant Nanopumping in Cylindrical Nanopores with Symmetry-Broken Gate Electrodes Alexander J Wagner, Aaron D Ratschow, Arka Das, Merete Seyfried, Steffen Hardt Gate electrodes in electrolyte-filled nanopores enable the precise control of transport processes for applications like DNA translocation or ionic current rectification. Recently, we demonstrated that applying unbiased ac voltages to conical, gated nanopores causes directional flows at intermediate frequencies, a phenomenon called resonant nanopumping. Here, we show the results of numerical simulations of the fully coupled Poisson-Nernst-Planck and Navier-Stokes equations in cylindrical nanopores with ac gate potentials. We show that breaking the symmetry with gate electrodes that partially cover the pore wall can substantially increase flow rates compared to conical pores. We identify the inherent timescales causing the resonance and formulate an analytical model that predicts the flow rates and the resonant dynamic behavior in accordance with our detailed simulations. Our results enable the efficient design and optimization of cylindrical resonant nanopumps, which, compared to conical designs, bear the potential of higher flow rates and simpler manufacturing for future experimental studies. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J18.00005: Ion Transport Enhancement in Nanofluidic Systems Using Counter-Charged Nanochannels: Insights from Simulations and Experiments Le ZHOU, Dachuang SHI, Shiji LIN, Yanguang ZHOU, Zhigang Li In this study, we introduce a novel approach to enhance ion transport in nanofluidic systems using counter-charged nanochannels, where half of the channels are positively charged while the other half are negatively charged. The idea is illustrated through molecular dynamics simulations and experiments. Simulations reveal that the ionic current in the proposed system can be 5.8 times higher than that in conventional fluidic systems with uniformly charged channels. The enhancement stems from the separated transport of cations and anions in positively and negatively charged channels, respectively, due to a lower effective energy barrier for the ion transport. Experimental results confirm the effectiveness of this approach. The findings presented in this research offer valuable insights for the optimization of various energy systems, including batteries and electrodes. |
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