Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D15: Droplets & Surfaces |
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Sponsoring Units: DFD Chair: Xiang Cheng, University of Minnesota Room: 304 |
Monday, March 3, 2014 2:30PM - 2:42PM |
D15.00001: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 2:42PM - 2:54PM |
D15.00002: Towards a more accurate microscopic description of the moving contact line problem -- incorporating nonlocal effects through a statistical mechanics framework Andreas Nold, Ben Goddard, David Sibley, Serafim Kalliadasis Multiscale effects play a predominant role in wetting phenomena such as the moving contact line. An accurate description is of paramount interest for a wide range of industrial applications, yet it is a matter of ongoing research, due to the difficulty of incorporating different physical effects in one model. Important small-scale phenomena are corrections to the attractive fluid-fluid and wall-fluid forces in inhomogeneous density distributions, which often previously have been accounted for by the disjoining pressure in an ad-hoc manner. We systematically derive a novel model for the description of a single-component liquid-vapor multiphase system which inherently incorporates these nonlocal effects. This derivation, which is inspired by statistical mechanics in the framework of colloidal density functional theory, is critically discussed with respect to its assumptions and restrictions. The model is then employed numerically to study a moving contact line of a liquid fluid displacing its vapor phase. We show how nonlocal physical effects are inherently incorporated by the model and describe how classical macroscopic results for the contact line motion are retrieved. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D15.00003: Droplet dynamics on chemically striped patterned surfaces Patrick Jansen, Kai Sotthewes, Harold Zandvliet, Stefan Kooij We study the dynamics of droplets on chemically striped patterned surfaces with alternating hydrophilic and hydrophobic stripes. A droplet deposited on such a surface typically adopts an elongated shape, due to preferential spreading; across the stripes spreading is more difficult than in the direction along the stripes. The shape evolution of a droplet on such a surface is investigated both in experiment, and numerical simulations employing the lattice Boltzmann technique. The shape is dependent on the path that is taken, the amount of kinetic energy, and the size of the droplet in comparison to the stripe dimension. Additionally, we also investigate the evaporation of water droplets on these surfaces. Elongated droplets evaporate markedly faster than spherical ones making the evaporation rate dependent on the striped pattern underneath the droplet. Finally, a gradient in surface energy can be constructed using these stripes, which enables droplet movement on the surface without applying additional external forces. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D15.00004: On the evolution of electrically charged toroidal droplets Alexandros Fragkopoulos, Ekapop Pairam, Alberto Fernandez-Nieves We can successfully generate viscous toroidal droplets suspended in another immiscible viscous liquid. Toroidal droplets are unstable due to surface tension and either break via a hydrodynamic instability similar to Rayleigh-Plateau or shrink until they collapse into a single spherical droplet. By applying a voltage difference across the droplet and a controlled ground we are able to charge the toroidal droplets. As a result, the surface tension now is in competition with the electrostatic repulsion due to the presence of the charge; this can change the evolution of the torus significantly. For instance, it can cause the expansion of the torus rather than its shrinkage, and also affects the wavelength of the fastest unstable mode. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D15.00005: Liquid drops on soft solids Luuk A. Lubbers, Joost H. Weijs, Siddhartha Das, Lorenzo Botto, Bruno Andreotti, Jacco H. Snoeijer A sessile drop can elastically deform a substrate by the action of capillary forces. The typical size of the deformation is given by the ratio of surface tension and the elastic modulus, $\gamma/E$, which can reach up to 10-100 microns for soft elastomers. In this talk we theoretically show that the contact angles of drops on such a surface exhibit two transitions when increasing $\gamma/E$: (i) the microsocopic geometry of the contact line first develops a Neumann-like cusp when $\gamma/E$ is of the order of few nanometers, (ii) the macroscopic angle of the drop is altered only when $\gamma/E$ reaches the size of the drop. Using the same framework we then show that two neighboring drops exhibit an effective interaction, mediated by the deformation of the elastic medium. This is in analogy to the well-known Cheerios effect, where small particles at a liquid interface attract each other due to the meniscus deformations. Here we reveal the nature of drop-drop interactions on a soft substrate by combining numerical and analytical calculations. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D15.00006: Investigating the stability of surface nanobubbles Robin Berkelaar, Erik Dietrich, Stefan Kooij, Harold Zandvliet, Detlef Lohse The primary attribute of interest of surface nanobubbles is their unusual stability and a number of theories trying to explain this have been put forward. Interestingly, the actual dissolution of nanobubbles is a topic that did not receive a lot of attention yet. We applied different experimental procedures in which gaseous nanobubbles should dissolve, according to the theories. In method A, the nanobubbles were exposed to a flow of degassed water for 96 hours. In method B, the ambient pressure was lowered in order to degas the liquid and the nanobubble-like objects. In method C, the liquid was evaporated and the geometry of the nanobubbles was indirectly studied in micrometers thick water films. The effects of these three methods on the stability of nanobubbles will be discussed. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D15.00007: Simulation of splashing of micro-scale droplets on a dry surface Arnout Boelens, Andrzej Latka, Michelle Driscoll, Irmgard Bischofberger, Cacey Stevens, Sidney Nagel, Juan de Pablo Results are presented for the simulation of micro-scale droplets splashing on a dry surface. The simulations are performed using a Volume Of Fluid approach and a Finite Volume technique. The contact line is described using a fixed microscopic contact angle. Both the gas phase and the liquid phase are assumed to be incompressible, and represent a two-phase system of ethanol in air. As the droplet approaches the wall, it changes shape and forms a dome over a thin gas layer between the droplet and the wall. As the gas gets squeezed out from under the droplet, it reaches velocities of up to 300 km/h, and there is a very large pressure spike at the edge of the droplet. The formation of a thin sheet of liquid is observed upon impact, which thickens near the edge of the sheet to reduce curvature. As the sheet begins to spread apparent contact angles are observed to approach 180 degrees. When lowering the gas pressure in the system, a higher gas velocity and relative pressure are observed on impact, and again a thin sheet forms. However, at low pressure the thin sheet stays closer to the wall. These observations are shown to be consistent with experimental measurements. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D15.00008: Study of 2D emulsions produced by Breath Figures of two immiscible substances Jos\'e Guadarrama-Cetina, Wenceslao Gonz\'alez-Vi\~nas In this work we analyze experimental results [1,2] on two condensing vapors (22 $^{\circ}$C) of ultrapure water (W) and Hexamethyldisiloxane (HMDSO) on a cold (5 $^{\circ}$C) repellent surface. From the statistics of population of the two kind of droplet patterns, we characterize statistically the emulsion formation through the parameters of occupancy, area fraction and diameter of droplet average per unit area and through the PDF of droplets diameter for each stage of the BF and its emulsion product. We compare those parameters and the PDFs for different straming rates of W/HMDSO and we give the necessary conditions to drive the system to stabilisation stage and cluster formation. \\[4pt] [1] J. Guadarrama {\sl et al.}, Phys. Rev. E {\bf 87}, 054401 (2013).\\[0pt] [2] J. Guadarrama {\sl et al.}. In preparation. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D15.00009: Micro bubbles at interfaces Gholamreza Keshavarzi, Anna Wang, Tracie Barber, Vinothan Manoharan The behaviour of a small micron sized bubbles close to an interface is vital to various interface interaction applications in several industries. Previous studies have focused on understanding the behaviour of large millimetric bubbles reaching an interface. Some of these millimetric bubbles are shown to bounce back [1], while others penetrate and burst on the interface resulting in possible small micron sized bubbles [2]. However, small micron sized bubble may act different. It has been observed that small microbubbles can act as if they are stabilized at the interface without merging to the fluid over the interface. The dynamics of the microbubble adsorption close to an interface has yet to be well understood.In this study we used digital holography microscopy to explore detailed information on the behaviour of the air microbubble at the interface. This study investigates the position and shape of a microbubble with respect to the interface. The dynamic behavior close to the interface along with where the small microbubble is positioned near an interface will help us in understanding the probability of penetration and merging back to the fluid on top. [1]Rise, bouncing and coalescence of bubbles impacting at a free surface, Colloids and surfaces A:Physicochemical and Engineering Aspects, Volume 365, Issues 1-3, pp. 36-762 (2010) [2]Daughter bubble cascades produced by folding of ruptured thin films, Nature, Volume 465, Issue 7299, pp. 759-762 (2010) [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D15.00010: Quantum Tunneling and Chaos in Classical Scale Walkers Jenny Su, Joshua Dijksman, Jeremy Ward, Robert Behringer We study the behavior of `walkers'; small droplets bouncing on a fluid layer vibrated at amplitudes just below the onset of Faraday instability. It was shown recently that despite their macroscopic size, the droplet dynamics are stochastic in nature and reminiscent of the dual particle-wave dynamics in the realm of quantum mechanics (Couder PRL 2006). We use these walkers to study how chaos, which is macroscopically unpredictable, will manifest in a quantum setting. Pecora showed in 2011 that tunneling for particles that have a chaotic ground state is different from tunneling for particles with a regular ground state (PRE 2011). In the experiment we gather data that illustrates the particle trajectory and tunneling behavior as particles transition across the barrier in the double well system with both integrable and chaotic shapes. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D15.00011: Cooling Enhancement by Drop Impact and Pool Boiling on Nano-textured Surfaces Under Normal Gravity Conditions and at Zero and Increased Gravity in Parabolic Flights Alexander Yarin, Suman Sinha-Ray, Seongchul Jun The earth experiments with drop impact onto metal-plated electrospun nanofiber mats encompass a single drop, or drop trains or jets impacts. The results on drop cooling and pool boiling on nano-textured surface were obtained during the parabolic flights supported by NASA and ESA. Pool boiling on nano-textured surfaces was studied for ethanol and water as working fluids. The nano-textured surfaces were copper platelets covered with copper-plated electrospun nanofibers. The results revealed that the heat flux in boiling on the nano-textured surfaces was about 3-8 times higher than that on the bare copper. This stems from the fact that nano-textured surfaces promote bubble growth by increasing the average temperature of fluid surrounding growing bubbles. Nano-textured surfaces facilitated bubble growth rate and increase bubble detachment frequency. On the other hand, the critical heat flux (CHF) on the nano-textured surfaces was found to be very close to its counterpart on the bare copper surfaces. However, the heat flux on the nano-textured surfaces in transition boiling was significantly higher than on the bare copper ones, since the presence of nanofibers prevented bubble merging and delayed formation of vapor film. [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D15.00012: Liquid drop impact on a granular surface Xiang Cheng, Runchen Zhao, Qianyun Zhang, Hendro Tjugito We investigate the impact of droplets onto a granular surface - a process that is likely familiar to all of us who have watched raindrops splashing on a sandy ground in a garden or on a beach. Combining high-speed photography with laser profilometry measurement, we experimentally study the 3D morphology of granular craters formed by liquid drop impact. By systemically varying the releasing height of liquid droplets, the wetting properties of granular particles, and the size ratio of droplets to particles, we show a scaling behavior of the size of craters and demonstrate a rich variation of the shape of granular residues in the center of craters. Based on liquid impact dynamics, a simple model is constructed to quantitatively explain the observed crater morphologies. Contrary to previous studies, our result suggests that the capillary interaction between particles and liquid is the main shaping force for the craters, and the drainage of liquid into the granular bed only plays a minor role in the process. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D15.00013: Emission modes in electrically-assisted coflow A.J. Hijano, J. Guerrero, A. Fernandez-Nieves, I.G. Loscertales We use glass-based microfluidic devices to study the emission regimes in electro-coflow. In addition to cone-jet and whipping, which are also seen in air or in the presence of a quiescent liquid bath, we also observe other regimes that where not observed before. One of these consists of a bent jet that remains confined to a plane that moves in time either periodically or aperiodically. We explore the effects of the inner and outer-fluid flow rates, their viscosity contrast and the applied voltage. [Preview Abstract] |
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