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 S04: Nano Flows |
Hide Abstracts |
Chair: Yuan-Nan Young, New Jersey Institute of Technology Room: 203 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S04.00001: Correlations at Liquid/Solid Interfaces Relating Molecular Configurational Effects to the Kapitza Resistance Hiroki Kaifu, Sandra Troian Today’s electronic systems for banking, medicine and transportation rely critically on ever more powerful integrated chips which can generate local power densities in excess of 100 W/cm$^2$ leading to catastrophic thermal failure. Such excess heat has become \textit{the limiting factor} in information processing. Liquid cooling is therefore being used to mitigate this problem. Fundamental understanding of thermal resistance at liquid/solid (L/S) interfaces is therefore indispensable to future design. Interfacial thermal transport is normally quantified by the Kapitza resistance although its relation to phonon transport at L/S interfaces is still lacking. Computational studies have mostly focused on the effects of liquid wettability and contact density, whose enhancement favors formation of absorbed layers that lower the resistance. Using non-equilibrium molecular dynamic simulations of a monoatomic Lennard-Jones liquid confined between solid walls, we examine interface configuration effects by varying the intermolecular distance representing the L/S potential minimum. These studies reveal how configuration of the liquid and solid molecules at the interface in the absence of liquid flow controls the magnitude of the Kapitza resistance. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S04.00002: Nanoscale Capillary Bridges and the Role of Hydration Forces Carlos Colosqui, Sijia Huang, Yuan Young, Howard Stone This talk presents results from theoretical and numerical analysis of a nano water bridge (of height 1 to 10 nm) studied via both fully atomistic molecular dynamics (MD) simulations and continuum-based models based on the Young-Laplace equation. For nanoscale separations between two flat walls, surface forces (e.g., van der Waals and hydration forces) significantly affect the capillary bridge shape, as well as the liquid-solid contact area and contact angle. Nevertheless, the local radius of the capillary bridge is reasonably well described by the classical Young-Laplace equation for surprisingly small heights of about 3 nm (i.e., 10 molecular layers). On the other hand, the curvature predicted by the classical Young-Laplace equation is constant and differs significantly from that reported by MD simulations. As a result, when the water bridge height is smaller than 5-10 nm we observe large differences between adhesion forces obtained from MD simulations and those predicted by Young-Laplace. To accurately account for results from fully atomistic MD simulations we must “extend” the Young-Laplace description by including a disjoining pressure that considers hydration forces associated with molecular layering and structural changes in the water near the walls. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S04.00003: Effect of Charge Inversion on Nanoconfined Flow of Multivalent Electrolyte Solutions Andres Rojano, Andres Cordoba, Jens Honore Walther, Harvey A. Zambrano Miniaturized devices integrated by nanoconduits have great potential for clinical and biotechnological analysis due to amplified sensibility, faster response and increased portability. The transport properties of an electrolyte solution flowing through a nanoconduit in which the electrical double layer occupies a considerable part of the cross section can be altered by the interfacial charge inversion (CI). Hence, an exhaustive understanding of the fluid transport in presence of CI is essential to develop more efficient nanofluidic devices. Here, molecular dynamics simulations of multivalent electrolyte solutions in silica nanochannels are conducted to study the effect of CI on hydrodynamic properties. The solutions consist of water as solvent, chlorine as co-ion and different shares of counter-ions i.e. sodium, magnesium and aluminum. From atomistic trajectories, we find that the magnitude of the effective viscosity is correlated to the concentration and valence of the counter-ions in the solution. Additionally, we show that the CI value is directly related to the hydration shell size of the counter-ions. Moreover, the results suggest that higher CI produces a gel-like region adjacent to the channel wall that increases the interfacial viscosity and friction coefficient. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S04.00004: Hydrodynamics in a Polymeric Nanoslit Pore with Graphene and Hexagonal Boron Nitride Wall Coatings: An Atomistic Study Diego Becerra, Andres Cordoba, Jens Honore Walther, Harvey A. Zambrano Design of efficient nanofluidic platforms requires effective reduction of flow resistance within the channel network. With this purpose, 2D-materials can be deposited on polymeric substrates increasing the transport efficiency of water solutions through nanopores. In the present work, we show that significant drag reduction can be achieved in a polyamide nanoslit pore by using graphene and boron nitride as wall coatings. Here, Molecular Dynamics simulations are performed to study water flow through uncoated and coated polyamide nanoslit pores. From atomistic trajectories, we investigate interfacial properties and evaluate the effect that the polymeric matrix has on water structure inside the pores. Furthermore, we compute density and temperature profiles, molecular orientations, friction coefficient and velocity profiles. Using these observables, we analyze the correlation between local water structure, flow enhancement and slip length. Our results indicate that in coated pores the interactions between water molecules and the underlying polyamide substrate have a significant influence on the flow rates. The insights reported in this work may assist the design of strategies to achieve low friction water transport in nanostructured pores. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S04.00005: Orientation change of multi-walled carbon nanotube forests under low-Reynolds shear flow Frans Jan de Jong, Adeline Buffet Due to their exceptional electrical, thermal and mechanical properties, multi-walled carbon nanotubes (MWCNTs) are popular for energy storage, biomedical applications and engineering. Indeed, due to the mechanical properties, MWCNTs show excellent sensing characteristics, which can be used for the development of sensors, e.g. liquid flow sensors, and actuators. Numerous dense packed upright standing MWCNTs form a so-called MWCNT forest. In the study presented here specifically tailored forests of MWCNTs are fixed in a microchannel and the orientation of the MWCNT forest is changed under shear flow, i.e. the MWCNT forest is tilted. The nonintrusive measurement technique microfocus small-angle X-ray scattering (muSAXS) is used to record the orientation change at various Reynolds numbers. The results show a linear relationship between the Reynolds number and the tilting of the MWCNT forest. Our investigations give an insight into the fluid structure interaction of MWCNT forests on the nanoscale. These findings constitute an important step in the understanding and thus the development of shear flow-induced stress sensors. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S04.00006: Size determines the adhesive rolling of nanoparticle: smaller rolls faster Huilin Ye, Zhiqiang Shen, Ying Li The adhesive rolling of nano-sized particle (NP) plays an essential role in the delivery of therapeutic or imaging agents to diseased microvasculatures. we investigate the adhesive behaviors of NPs on a substrate under the shear flow. Based on the energy balance analysis, we theoretically derive the steady rolling equation for different sized NPs. Contrary to the fundamental Stokes prediction, it is found that smaller NPs move faster than their larger counterparts under the ligand-receptor binding (LRB) effect. Further, the hydrodynamic strength (quantified by shear rate $\gamma )$ is demonstrated to be associated with the steady rolling velocity (v) of NPs as R$^{\mathrm{\sim 0.2\thinspace }}$(R is radius of NP). This scaling is attributed to the size dependence of the adhesive kinetics that is described by energy based stochastic model. We also find the enlargement of flow strength will trigger the transition from adhesive rolling to free rolling of NPs, due to the saturation of stretching of biological bonds forming between ligands and receptors. The size dependence of the rolling behavior may provide a guidance for engineering efficient NPs in biomedical applications. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S04.00007: Describing the Mechanics of Fluid-Solid Interfaces using Molecular Modeling Nicolas Hadjiconstantinou, Gerald Wang Fluid-solid interfaces are ubiquitous in fluid dynamics, but also particularly important at the nanoscale, where the spatial extent of fluid under bulk conditions is very limited. Predicting fluid behavior at such an interface requires an understanding of the fluid structure, as well as the molecular mechanics of fluid motion under the influence of the solid potential. In this talk, we describe molecular approaches for characterizing these phenomena, with particular emphasis on the resulting slip at the interface. In the case of a simple fluid, we show that molecular-kinetic considerations can be used to develop a universal scaling law for slip that reduces to Navier slip at low shear rates and connects macroscopic transport quantities (e.g. the slip length) to the microscopic system description. In the case of immiscible two-phase flow, we demonstrate that as characteristic lengthscales become small, interfacial hydrodynamic bending becomes negligible and, as a result, instead of Tanner's law, the contact angle is described by Blake's molecular-kinetic theory which connects the deviation from the equilibrium contact angle to the amount of slip. Our models are supported by extensive molecular-dynamics simulations, as well as evidence from some directly comparable experiments. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S04.00008: Measuring the hydrodynamic wall position and viscoelastic friction coefficient by molecular dynamics Takeshi Omori, Naoki Inoue, Laurent Joly, Samy Merabia, Yasutaka Yamaguchi Flows in nanofluidic systems are controlled by the hydrodynamic boundary condition (BC), involving the friction coefficient and the hydrodynamic wall position. Here we considered a liquid nano-slab confined between two walls, where we derived, from the Stokes equation and the Navier slip BC, analytical expressions for the liquid response to an oscillatory tangential motion of the walls in terms of the wall shear stress and mean fluid velocity. By fitting these expressions to molecular dynamics simulation results, we could extract both the viscoelastic friction coefficient and hydrodynamic wall position for walls with three different wettabilities, hence fully characterizing the frequency-dependent hydrodynamic boundary condition. The proposed method could be applied to a variety of liquid-solid interfaces of interest, e.g. for flows of complex fluids or fluids at a low temperature. It should also support methodological developments on the characterization of the hydrodynamic slip in general, including the further development of the quartz crystal microbalance measurement technique. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700