Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B36: Electrokinetic Flows: Nanochannels, Surface Conduction and Ionization |
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Chair: Ali Mani, Stanford Room: 618 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B36.00001: Application of Nonlinear Electrokinetic Transport using Network Heterogeneity of Porous Media Hyekyung Lee, Ali Mani, Sung Jae Kim Nanoscale electrokinetic transport through perm-selective membranes has been actively researched using a micro/nanofluidic platform recently. The ion depletion layer formed near the membrane under dc bias can be compartmentalized using heterogeneous microchannels and a numerical/experimental study using the simplified porous media demonstrated an internal recirculation flow due to different hydraulic resistance in network of channels. Furthermore, overlimiting current significantly increased due to this flow so that the channel with the higher resistance played as the main current path. In this presentation, we applied this mechanism to practical engineering problems. First, we investigated electrokinetics by laying a permselective membrane on only the main current path. By comparing the devices either with uniformly patterned membrane vs non-uniformly patterned membrane (i.e. membrane only at the current paths), a similar perm-selective ion transportation was measured, leading to the same mass transfer but the half of membrane material cost. Second, it is expected that network effect could localize the membrane fouling because the mass transfer is dominant through the main current path. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B36.00002: Capacitive Charging of Multi-ion Electrolytes confined in parallel electrodes Yun Sung Park, In Seok Kang Charging and discharging of ionic devices have been widely studied theoretically and experimentally. Especially, numerous kinds of electrolytes and their combinations have been utilized in order to enhance capacitances or frequency dependencies of the devices. However, the theoretical studies of effects of multiple ions on the properties of the devices are insufficient. In this work, we study the effect of multiple ions quantitatively using continuum approach. Electrolytes are confined in one-dimensional parallel electrodes, which is simplest system for many ionic devices. The multiple ions with different sizes and valences are chosen and their effects are compared along with the sparse and dense bulk concentrations. We focus on both the equilibrium distributions and the dynamic behaviors of ions, which are related to capacitances and frequency dependencies, respectively. The quantitative analyses are done numerically by dividing charge densities and fluxes of individual ions. Lastly, simple electroosmotic flows are calculated from the obtained charge densities. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B36.00003: Negative Pressure of Ionic Liquids Inside a Nanoslit: Molecular Dynamics Study Yu Dong Yang, Jung Min Oh, In Seok Kang Predicting the force the acting on the charged surface is important to prevent deformation or swelling of pores. When the electrostatic interaction between charged pore and its counter-ions is predominant, the internal electrolyte can pull the wall. This means the total pressure becomes negative. Since it becomes complicated to predict with considering the large size and complex shape of ionic liquids, molecular dynamics simulations are conducted to analyze the pressure acting on the nanoslit wall. The pressure change with respect to the slit width under 1 nm scale was analyzed using coarse-grained model, and it is determined by the competition between the contact and electrostatic component of the total pressure. When the slit width is below a double of each ion size, the negative pressure scale is about O (103 atm) and it is 20 to 40 times the bulk osmotic pressure of each ionic liquids. The ion shape or size is related to the magnitude of contact component, but it hardly affects the negative pressure when the electrostatic component is dominant due to the ion re-arrangement in a slit. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B36.00004: Understanding the electrokinetic interaction between dynamically tunable nanofluidic channels connected in series. Barak Sabbagh, Elad Stolovicki, Gilad Yossifon The passage of an electric current through a permselective medium results a phenomenon termed concentration polarization (CP). This phenomenon has been the focus of intensive research, particularly regarding its relationship with microfluidic applications, e.g. on-chip desalination and enhanced biosensing sensitivity. These applications have been limited by a fixed geometry and properties of the permselective medium (i.e. nanochannel) which defines the location, intensity and length of the CP layer. The ability to dynamically tune the geometry of the permselective medium allows us to optimize existing processes and opens up new application possibilities. This is realized using pneumatically controlled microvalves where the formed gap between the elastically deformed membrane, which is controlled by external pressure chamber, and the microchannel, forms the ion permselective nanochannel. In contrast to previous studies of such a system, here we extend this approach to several individually addressable microvalves that are connected in series within the same microchannel. Such interaction between two or more dynamically formed nanochannels yields interesting results of both the transient and steady-state behavior of the CP layers and related electrical response. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B36.00005: Revisiting, resolving and unifying the nanochannel-microchannel electrical resistance paradigm Ramadan Abu-Rjal, Ran Eshel, Yoav Green Until recently, the accepted paradigm was that the Ohmic electrical response of nanochannel-microchannel systems is determined solely by the nanochannel while the effects of the adjacent microchannels ae negligible. Two, almost identical, models were suggested to rationalize experimental observations that appeared to confirm the paradigm. However, recent works have challenged this paradigm and showed it be incorrect, namely, the microchannels contribute in a non-negligible manner. Two newer nanochannel-microchannel models were suggested to replace the nanochannel-only models. These models were asymptotic solutions limited to either very low or very high concentrations. Here, we review these four leading models. The most popular is shown to be incorrect, while the remaining models are unified under a newly derived solution which shows remarkable correspondence to simulations and experiments. The unifying model can be used to improve the design of any nanofluidic based systems as the physics are more transparent, and the need for complicated time-consuming preliminary simulations and experiments has been eliminated. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B36.00006: Enhanced Electrokinetic Energy Conversion {\&} Ion-Selective Transport in Macroscopic Vertically Aligned BNNT Membranes Semih Cetindag, Aaditya Pendse, Robert F. Praino, Sangil Kim, Jerry W. Shan Recent nanofluidic experiments with single or few nanopores in graphene, MoS$_{\mathrm{2}}$ and h-BN have shown unique fluidic transport properties and the potential for electrokinetic energy conversion with unprecedented power densities. In such nanopores, the high-surface charge makes possible a diffusio-osmotic mechanism for ion-selective transport, distinct from the Donnan exclusion in the conventional membranes. Here, we describe the fabrication of the first-ever macroscopic vertically aligned boron-nitride nanotube (VA-BNNT) membranes, and our study of their ion-selectivity mechanisms and osmotic-power-generation performance. We show that the VA-BNNT membranes are highly cation-selective even when the Debye length is smaller than the inner-pore radius of the nanotubes. Moreover, the membranes exhibit osmotic-energy-conversion efficiencies of 30{\%}, and have osmotic power densities (based on open pore area) comparable to and even exceeding that of single BNNTs, up to 7,500 W/m$^{\mathrm{2}}$ at pH 11 for a 1M:1mM KCl molarity difference. This osmotic power density increase with increasing surface-charge density at higher pH, but remain substantial even at pH 7. To further elucidate the mechanism(s) for the ion selectivity, we compare the power generation and transport rates of the VA-BNNT membranes for salts having different cation and anion diffusivities and thus diffusio-osmotic parameters. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B36.00007: ABSTRACT WITHDRAWN |
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