Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E06: Electrokinetics: Ion-Selective Interfaces |
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Chair: Sung Jae Kim, Seoul National University Room: Georgia World Congress Center B208 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E06.00001: Transient response of undulated microchannel-nanochannel interface device Neta Zalmanovich, Ramadan Abu-Rjal, Sinwook Park, Gilad Yossifon In this work we present a microchannel–nanochannel interface device with sinusoidal undulation of the interface. In the under-limiting region the response of a microchannel-nanochannel interface device is similar to an ion-selective membrane device with straight interface and exhibits a monotonic chronopotentiometric and chronoamperometric responses. Beyond the limiting current the ionic perm-selectivity of the nanochannel and electroconvection affect the transient response and result in a non-monotonic response. Specifically, in the chronoamperometric response for example, the non-ideal perm-selective nanochannel results in concentration-polarization within the nanochannel which contributes to a non-monotonic response (maximum), followed by another non-monotonic response (minimum) when electroconvection becomes strong enough to affect the depletion layer. The response strongly depends on the undulation of the interface, e.g. amplitude and wavelength, and the selectivity of the nanochannel. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E06.00002: Experimental Investigation on Spatiotemporal Concentration Profile of the Ion Concentration Polarization Layer Junsuk Kim, Sung Jae Kim Ion Concentration Polarization (ICP) is a fundamental electrokinetic phenomenon that occurs near a perm-selective membrane. With the balance of hydrodynamic drag force and electrophoretic force on the charged molecules, ICP can be applied to a preconcentrator for the detection of low abundant molecules. In this work, spatiotemporal concentration profile of diffusion-convection layer during ICP process had been measured with patterned microelectrode. Here, diffusion-convection layer was defined as the intermediate region between bulk region and ion depletion zone. Unlike the traditional diffusion-convection layer which had linear concentration profile, the measured data indicated near plateau concentration distribution over the diffusion-convection layer in a microfluidic environment. Also, even though the plateau concentration region had rather higher concentration compare to ion depletion zone, it acted as a virtual barrier against charged molecules as well. This anomalous concentration profile can provide a key information to the fundamental study on preconcentration dynamics of ICP. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E06.00003: Non-negligible transient effect on perm-selective ion transportation Soonhyun Kwon, Hyomin Lee, Sung Jae Kim Perm-selective ion transportation has been extensively utilized in various micro/nanofluidic applications. While a steady state assumption was typically adopted to characterize the device, here we experimentally demonstrated that there is inevitable transient effect on the perm-selective ion transportation, especially low Reynolds number environment. The voltage/current (V-C) measurement in micro/nanofluidic platform often showed that current were bumped up in limiting current regime (i.e. overshoot) unlike theoretical results of steady state assumption. In this work, we measured V-C in dead-end channel connected by side channel. Buffer liquid was continuously injected from the side channel so that a constant electrolyte concentration was kept from the side channel to reservoir. Extending the distance from membrane to the side channel resulted in more severe overshoot effect, meaning there is non-negligible transient effect on the ion transportation through membrane. Conclusively, this transient effect should be considered in designing energy-related micro/nanofluidic application. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E06.00004: Spontaneous Particle Separation using Water-absorbing Nanoporous Ion Exchange Medium Dokeun Lee, Jung A Lee, Hyomin Lee, Sung Jae Kim Manipulating mechanism of particle’s motion has been extensively studied for the sample preparation in microfluidic applications including diagnostics and biological analyses. However, most of conventional methods need additional external forces such as electric field or pressure and complicated channel designs, which demands highly complex fabrication processes. In this work, power-free manipulation of particle’s motion was suggested based on leveraging convective flow over diffusiophoresis near the water-absorbing nanoporous ion exchange medium, which was verified both by simulation and experiment. As a result, the direction of particle’s motion was controlled at one’s discretion, which led to the selective preconcentration of particles having different zeta potential. Also, design rule for maximizing the efficiency was suggested. Thus, this spontaneous particle separation method would be used as a key component in power-free lab on a chip applications. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E06.00005: Ion transport in an annular geometry: limiting current, concentration polarization and vortex formation Zhibo Gu, Bingrui Xu, Peng Huo, Daosheng Deng Ion transport playing a key role for water treatment and energy storage has been extensively studied in a parallel geometry. Here we explore the ion transport in a novel annular geometry experimentally. The limiting current depends on both the direction of electric field and the radius of the inner electrode. In the region of overlimiting current, we directly visualize the vortex formation and dynamical evolution near the cathode side. Moreover, we directly observe the propagation of concentration depletion from the cathode side toward the anode side, and the propagation velocity agrees well with the theory as well. These results have implications for desalination, biomolecular detection and improving battery performance. |
Sunday, November 18, 2018 6:15PM - 6:28PM |
E06.00006: A current-voltage response for unipolar conical nanochannel diodes Yoav Green Permselective nanochannels can rectify the electric current transported through them similar to solid-state diodes. The rectification is due to symmetry breaking related to the distribution of the nanochannels surface charge as well the geometry. Thus far, most of the related works to the asymmetric current response have been primarily experimental. In this talk I will present an analytical solution for the concentration distribution, electric potential and current-voltage relation (I-V) response for a conical shaped nanochannel with a non-homogeneous surface charge. The I-V is shown to behave like a unipolar diode with the rectification depending on the surface charge and geometry with rectification factors of more than O(100). The theoretically predicted results for 1D and 2D systems are confirmed by numerical simulations. |
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