Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K48: Thin Films, Surface Flows, Interfaces and Microfluidics IFocus
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Sponsoring Units: DFD GSOFT GSNP Chair: Baiou Shi, Penn State Erie Room: BCEC 251 |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K48.00001: When Salty Water Meets a Hydrophobic Surface Adele Poynor, ANTHONY FLORIMBIO, Cayton Hornberger, Zachary Zoll The investigation of how water meets a hydrophobic surface suggests that a very low-density layer, called the depletion layer, forms to mitigate the loss of hydrogen bonds at the surface. Salt disrupts the hydrogen-bonding network of water and therefore is expected to affect the formation of the depletion layer. We study this interface using the quantum optical technique of Surface Plasmon Resonance (SPR) for self-assembled monolayers (SAMs) in different aqueous salt solutions. |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K48.00002: Constant-rate capillary rise in wettability-controlled tubes Bauyrzhan Primkulov, Amir Pahlavan, Ruben Juanes Displacement of a viscous liquid by a less-viscous liquid from the solid surfaces is relevant to many practical applications, including flow through porous chemical reactors, immiscible pollutant transport in soils, and hydrocarbon recovery. We study the spontaneous imbibition of water in capillary tubes partially filled with oil slugs of fixed length. High viscosity contrast of viscous-oil with water results in a tunable constant-rate capillary rise. The capability to control both the displacement rates and wettability makes this an attractive system to explore, and the results of the study bear a direct connection to the multiphase flow in porous media, where wettability plays a critical role. |
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K48.00003: Capillary Flow Dynamics in Open Triangular Grooves: From Flatland to Curvy 3D Trajectories Nicholas White, Sandra Troian Capillary flow in straight open triangular grooves finds widespread use in applications such as point-of-care biomedical devices, heat pipes for cooling microelectronics and spacecraft propellant management. Advances in 3D printing and other patterning techniques can now be used to fabricate compact open curved channels in 3D. This capability introduces the potential for multi-layer and multi-functional operation of many types of microfluidic and optofluidic chips. Romero and Yost (1996) and Weislogel (1996) first elucidated how the streamwise gradient in capillary pressure due to the change in curvature of the fluid interface due to local variations in film thickness induces rapid wicking of slender films into straight and open triangular grooves. Here we present an analytic model which extends that original work to arbitrarily curved open triangular grooves in 3D. Despite the complex flow trajectories which can ensue, a first order perturbation analysis yields a compact equation for the moving interface. This finding should be of use to the design and implementation of next generation 3D fluidic devices. |
Wednesday, March 6, 2019 8:36AM - 8:48AM |
K48.00004: Capillary Forces Computation for Nano-suspension Droplet Spreading: Molecular Dynamics Simulations Baiou Shi, Weizhou Zhou, Edmund B Webb III With the development of nano-technology, nano-suspension provides us a path to synthesize and disperse nano-particles in fluids, and it has been widely utilized in pharmaceutical and semiconductor industries. Recently, many studies via both experiments and simulations have focused on nano-suspension droplets dynamic spreading and further evaporation on solid surfaces. However, the underlying physics and especially the fundamental driving forces controlling the kinetics of nano-suspension wetting and spreading is still unknown. In this talk, results from molecular dynamics simulations are presented with emphasis on computing capillary forces between advancing liquid fronts and suspended particles. Meanwhile, the effect of nano-particle size, particle loading, and interaction strength examined from atomic scale simulations will be presented. For increasing particle size, a dramatic change of wetting behavior from de-pinning to pinning is observed and also interpreted as the increasing capillary force between suspended nano-particles and the three-phase interface. By tuning down the interaction between the particle and the underlying substrate, de-pinning is observed instead of the exhibiting pinning behavior. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K48.00005: Water Filtration in Carbon Nanotubes Resulting From Electronic Friction at the Walls Jeffrey Sokoloff In this talk, a mechanism for removal of salt from salt water is discussed, which results from friction due to Ohm’s law heating, resulting from motion of an electron charge induced in the tube walls by the water molecules’ dipoles and the ions’ charges. The filtration occurs because this friction is larger for salt ions than for water molecules. Friction due to Ohm’s law heating might also provide an explanation for the observation by Secchi, et. al., that the flow velocity of water in carbon nanotubes increases rapidly as the tube radius decreases from 50 to 15nm, which does not occur for boron nitride nanotubes which are insulators. This friction is large enough to produce the observed slip-lengths. One possibility is that the nanotubes in this experiment were metallic, whose conductivity becomes large as their radius decreases, due to ballistic conduction. Another possibility is that when the tube circumference drops below the electron mean free path, the wall switches from behaving as a two dimensional conductor to behaving as a one dimensional conductor for which the electrons are more strongly localized. For sufficiently small conductivity, small distortions of the localized states can provide the dominant contribution to the induced charge, rather than current flow. |
Wednesday, March 6, 2019 9:00AM - 9:12AM |
K48.00006: Laser streaming: A novel photoacoustic streaming principle and its application in microfluidic driving Shuai Yue, Yanan Wang, Qiuhui Zhang, Feng Lin, Nzumbe Epie, Suchuan Dong, xiaonan shan, Dong Liu, Wei-Kan Chu, Zhiming Wang, Jiming Bao
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Wednesday, March 6, 2019 9:12AM - 9:24AM |
K48.00007: Alignment-dependent growth of unstable patterns in liquid crystals Qing Zhang, Shuang Zhou, Irmgard Bischofberger The displacement of a more viscous fluid by a less viscous one in a quasi-two dimensional geometry leads to the formation of complex fingering patterns. In isotropic systems, disordered dense-branching morphologies arise from repeated tip-splitting of the evolving finger. In anisotropic systems, by contrast, the growth morphology changes to a highly ordered dendritic growth characterized by stable needle-like protrusions decorated with regular side-branches. We investigate such morphology transitions between dendritic growth and dense-branching growth in an intrinsically anisotropic liquid, a lyotropic chromonic liquid crystal in the nematic phase. We show that the transition depends on three parameters; the interface velocity, the concentration of liquid crystal and the viscosity ratio between the less-viscous inner fluid and the more-viscous outer liquid crystal. Remarkably, we find that different aspects of the patterns are experiencing environments of different viscosities; the characteristics of the locally-determined most unstable wavelength are governed by a viscosity that is 20 times lower than that governing the relative length of the fingers. We discuss how these two different viscosities are related to the local alignment of the liquid crystal. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K48.00008: Electrokinetics in pH-responsive polyelectrolyte-brush-grafted nanochannels: Effect of the appropriate Strong Stretching Theory representation of the polyelectrolytes Siddhartha Das, Harnoor Singh Sachar, Vishal Sankar Sivasankar Functionalization nanochannels with polyelectrolyte (PE) brushes, contrary to the classical notion, has recently been established to augment electroosmotic (EOS) transport in nanochannels under special conditions where charges of the brushes are localized at the non-grafted ends of the PEs. Here we shall re-visit these calculations as well consider the more readily encountered situations where the entire PE molecule is charged in presence of the most rigorous framework where the PE brushes are modeled using the Strong Stretching Theory (SST) that accounts for the excluded volume (EV) effects and the effect of considering a generalized mass action law. These considerations would significantly affect the monomer distribution (which in turn would affect the drag force imparted by PE brushes) and the resulting EDL (electric double layer) electrostatics (which in turn would affect the EOS body force). This model would be the first rigorous theory for the electrohydrodynamics in the PE-brush-functionalized nanochannels accounting for the appropriate coupled thermodynamic representation of the PE brush configurations and the EDL electrostatics. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K48.00009: Direct measurement of capillary attraction between floating disks Ian Ho, Giuseppe Pucci, Daniel M Harris It is well known that two particles trapped at a fluid interface may interact due to the deformation they induce on the free surface. In the present work, we present direct measurements of the force between centimetric superhydrophobic disks resting on an air-water interface. Using a novel experimental setup, we characterize how the attraction force depends on the disk mass, diameter, and relative spacing. Our measurements are compared with theoretical predictions. Future directions will be discussed. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K48.00010: Nanomechanical Measurement of the Thermal Fluctuation Spectrum of a Liquid Atakan Ari, Mehmet Selim Hanay, Mark Richard Paul, Kamil Ekinci It is challenging to measure the fluctuating Langevin force, which gives rise to thermal fluctuations in a system. Here, we explore a novel approach for measuring the spectrum of thermal fluctuations in a liquid using a nanomechanical resonator. First, the nanomechanical resonator is coherently driven in the liquid at an amplitude above its thermal noise within the linear response regime. The drive force is provided by an electrothermal actuator, while the displacement is measured using optical interferometry. Separately, the position fluctuations of the resonator are measured. The spring constant, and hence the linear response function, of the resonator is determined from the equipartition theorem and the linear response of the resonator. Since the Langevin force excites the thermal fluctuations of the resonator in proportion to the square of the linear response function, it is then possible to extract the spectrum of the thermal force. We compare our experimental measurements with a theoretical description that assumes a long and thin beam fluctuating in a viscous fluid with a frequency dependent thermal driving force. We observe that the thermal force spectrum is a monotonically increasing function of frequency. |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K48.00011: Thickness Dependent Nanofluidic Transport in Nanopores and Nanochannels Mohammad Heiranian, N. R. Aluru Due to the high performance water transport through ultrathin membranes, nanopores and nanochannels have drawn a great deal of attention in a variety of applications, such as water desalination, power generation and biosensing. Classically, the transport rate scales inversely with the thickness. However, transport in carbon-based nanopores and nanochannels far exceeds the classical transport governed by the Hagen-Poiseuille (HP) equation, suggesting large transport enhancement factors with respect to the permeation predicted by HP. Here, using molecular dynamics simulations we characterize the thickness dependence by studying the hydrodynamical properties of pores and channels in graphene and finite-length CNTs. Transport in graphene and short CNTs is shown to be dominated by a high interfacial friction and viscosity at the pore/channel entrance. A corrected Hagen-Poiseuille (CHP) model, based on viscosity and friction from Green-Kubo relations, successfully predicts the non-equilibrium pressure driven flows for different sizes of channels. The previously reported enhancement factors (of the order of 1000) approach unity when the permeations are normalized by that of the CHP. The results of our study will help better understand nanoscale flows in nanopores and nanochannels. |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K48.00012: WITHDRAWN ABSTRACT
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Wednesday, March 6, 2019 10:24AM - 10:36AM |
K48.00013: Dynamical measurements of receding contact angle for evaporating drops Chloe Lindeman, Nicholas Schade, Sidney Robert Nagel We study the receding contact angle of drops during evaporation. Drops of a dyed solution are allowed to evaporate for some time τ before they are removed via a small hole in the substrate. We record the contact angle as the fluid is removed and extract the receding contact angle — that is, the angle at which the drop first depins — as a function of τ and dye concentration. For low τ (i.e., immediate drop removal), the receding contact angle depends only weakly on concentration. For τ on the order of a few minutes, the receding contact angle decreases with a growing dependence on concentration. This suggests that the concentration of solute near the drop edge grows due to the flows induced by evaporation as in the coffee-ring effect. Surprisingly, even pure water exhibits a significant τ-dependent receding contact angle. |
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