Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L19: Nanofluids I |
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Chair: Sandip Ghosal, Northwestern University Room: 310/311 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L19.00001: Overlimiting current through ion concentration polarization layer: Hydrodynamic convection effects Inhee Cho, Sung Jae Kim In this presentation, we experimentally investigated an effect of the hydrodymanic convective flow on an ion transport through nanoporous membrane in a micro/nanofluidic system. The convective motion of ions in an ion concentration polarization zone was controlled by external hydrodynamic inflows adjacent to the nanoporous membrane. The ion depletion region (which is regarded as a high electrical resistance) is spatially confined to a triangular shape with an additional hydrodymanic convective flow, resulting in a significant alternation in classical liming current value. Furthermore, the extreme spatial confinement can completely eliminate the limiting current region at higher flow rate so that one can obtain high current value which turns to be high power efficiency. Therefore, this mechanism would be utilized as minimizing power consumption for various electrochemical membrane systems such as fuel-cell, electro-desalination system and nanofluidic preconcentrator, etc. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L19.00002: Hydrodynamic flow in the vicinity of a nanopore in response to an applied voltage Mao Mao, Sandip Ghosal, Guohui Hu Continuum simulation and analytical modeling is employed to study ion transport and fluid flow through a nanopore in a solid-state membrane under an applied voltage. The ion distribution near the surface of the membrane arises due to the combined effect of the intrinsic surface charge as well as concentration polarization due to the applied field. It gives rise to an electric pressure that drives hydrodynamic flow in the vicinity of the pore. There is a net hydrodynamic flow through the nanopore due to the asymmetry in the Debye layer induced by the membrane surface charge. The qualitative behavior is similar to that observed in a previous study using molecular dynamic simulations. The flow strength is a strongly nonlinear function of the applied field. Combination of electrophoretic and hydrodynamic effects can lead to ion selectivity in terms of valences and this could have some practical applications in separations. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L19.00003: Effect of chain stiffness on interfacial slip in nanoscale polymer films Nikolai Priezjev The results obtained from molecular dynamics simulations of the friction at an interface between polymer melts and weakly attractive crystalline surfaces are reported. We consider a coarse-grained bead-spring model of linear chains with adjustable intrinsic stiffness. The structure and relaxation dynamics of polymer chains near interfaces are quantified by the radius of gyration and decay of the time autocorrelation function of the first normal mode. We found that the friction coefficient at small slip velocities exhibits a distinct maximum which appears due to shear-induced alignment of semiflexible chain segments in contact with solid walls. At large slip velocities, the friction coefficient is independent of the chain stiffness. The data for the friction coefficient and shear viscosity are used to elucidate main trends in the nonlinear shear rate dependence of the slip length. The influence of chain stiffness on the relationship between the friction coefficient and the structure factor in the first fluid layer is discussed. Financial support from the National Science Foundation (CBET-1033662) is gratefully acknowledged. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L19.00004: Diffusion Monte Carlo ab initio calculations to study wetting properties of graphene Yanbin Wu, Huihuo Zheng, Lucas Wagner, N.R. Aluru For applications of graphene in water, including for example desalination and DNA sequencing, it is critical to understand the wetting properties of graphene. In this work, we investigate the wetting properties using data from highly accurate diffusion quantum Monte Carlo (DMC) calculations, which treat electron correlation explicitly. Our DMC data show a strong graphene-water interaction, indicating graphene surface is more hydrophilic than previously believed. This has been recently confirmed by experiments [Li et al. Nat. Mater. 2013, doi:10.1038/nmat3709]. The unusually strong interaction can be attributed to weak bonding formed between graphene and water. Besides its inadequate description of dispersion interactions as commonly reported in the literature, density function theory (DFT) fails to describe the correct charge transfer, which leads to an underestimate of graphene-water binding energy. Our DMC calculations can provide insight to experimentalists seeking to understand water-graphene interfaces and to theorists improving DFT for weakly bound systems. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L19.00005: Prediction of the effective force on DNA in a nanopore based on density functional theory Guohui Hu, Wenyue Tang We consider double-strand DNA voltage-driven translocation through a nanopore in the present study. By assuming the DNA is coaxial with the cylindrical nanopore, a hydrodynamic model for determining effective force on a single DNA molecule in a nanopore was presented, in which density functional theory (DFT) combined with the continuum Navier-Stokes (NS) equations is utilized to investigate electro-osmotic flow and the viscous drag force acting on the DNA inside a nanopore. Surface charge on the walls of the nanopore is also taken into account in our model. The consistence between our calculation and the previous experimental measurement indicates that the present theoretical model is an effective tool to predict the hydrodynamic resistance on DNA. Results show that charge inversion, which cannot be obtained by the Poisson-Boltzmann (PB) model, will reduce electro-osmotic velocity, or even lead to flow reversal for higher salt concentration. This is helpful to raise the effective force profoundly in the overscreening region. [Preview Abstract] |
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