Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session M12: Drops: Wetting and Spreading I |
Hide Abstracts |
Chair: Martin Brinkmann, Max Planck Gesellschaft Room: 3018 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M12.00001: Hydrodynamics of micro-scale surface flows induced by triangulated droplet stream impingement array Taolue Zhang, Jorge Alvarado, Anoop Kanjirakat, Reza Sadr A study of surface flow hydrodynamics caused by triple stream of impinging droplets arranged in a triangular array is presented. Triple streams of mono-dispersed droplets were produced using a piezoelectric droplet generator with the ability to adjust parameters such as droplet impingement frequency, droplet diameter, droplet velocity and spacing between adjacent impinging droplet streams. A translucent Zinc Selenide (ZnSe) substrate was used for characterizing the hydrodynamic phenomena of the droplet impingement zone using a high speed imaging technique. Surface jet-like fluid flows were observed among impact craters during the high-frequency droplet impingement process. A transition from laminar-like to turbulent-like surface jet flow was observed by increasing droplet Weber number or decreasing droplet impingement spacing. A correlation based on visual observations has been postulated by taking into account the droplets' Weber number ($We)$ and non-dimensional droplet impingement spacing ($S^{\ast}$). The correlation has a mathematical form of $S^{\ast }\cdot We^{n}=K$, where $K$ is a constant. One major result from the study is the relative accuracy of the postulated model in predicting the laminar-turbulent like transition in terms of $We$ and $S^{\ast }$. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M12.00002: Droplet Spreading with Sol-Gel Transition Maziyar Jalaal, Boris Stoeber, Neil J. Balmforth The impact and spreading of liquid droplets on a smooth solid substrate is a classical subject with several industrial applications such as ink-jet printing, spray cooling, coating, and many others. For many of these deposition processes, controlling the final shape of the drop is critical. In the current research, a new technique for controlling the spreading of droplets impacting a substrate is presented. This technique exploits the rheology of a thermo-responsive polymer solution that undergoes a reversible sol/gel transition above a critical temperature. Experiments are conducted using a combination of shadowgraphy and micro-PIV to observe spreading drops. It is shown that the final diameter of a droplet can be controlled through the temperature of the substrate and the tunable sol/gel transition temperature of the fluid.A mathematical model is provided to further elucidate the flow dynamics. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M12.00003: Advancing contact angles on large structured surfaces Yumiko Yoshitake, Yoshinori Itakura, Junichi Gobo, Tsutomu Takahashi To understand wetting phenomena on complex surfaces, simple modeling experiments in two-dimension system would be one of the most efficient approaches. We develop a new experimental method for wetting dynamics using a large pseudo two- dimensional droplet. This method is useful to examine theoretical studies developed in two dimensional systems. In this study, we examine a pinning and depinning phenomena on millimeter-size structured surface to explain the origin of contact angle hysteresis. Contact lines of the droplet are pinned and deppined at the edge of surface texture. The contact lines can move when the contact angle is equal to the Young's contact angle which are determined by the balance of the surface and interfacial tension immediate vicinity of the contact lines, which is different from the Wenzel's low. Our approach enables to realize a macroscopic modelling experiment of wetting on complex surfaces, which opens a path to design functional surfaces with chemical and physical structure. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M12.00004: Sessile drops and condensation on chemically patterned micropillars Orest Shardt, Prashant Waghmare, Daniel Orejon, Naga Gunda, Yasuyuki Takata, Sushanta Mitra We examine the state of sessile drops on silicon micropillars with patterned wettability as well as condensation of water onto such surfaces. These patterned micropillar arrays were created by treatment with a perfluoroalkylsilane to create a hydrophobic surface and subsequent patterning with sodium hydroxide solution to create hydrophilic regions. The surfaces were characterized by measuring the contact angles and observing the states of sessile drops, and the results are compared with those of uniformly hydrophobic and hydrophilic pillars. The nature of condensation onto patterned pillars has been examined with environmental scanning electron microscopy (ESEM). The results show the initial dropwise condensation on the different types of pillars and the transition to a film. Surfaces that combine texturing with chemical patterning could be useful for enhanced control of condensation and droplet motion. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M12.00005: Electrostatically-driven precursor films Seyed Reza Mahmoudi, Kripa K. Varanasi Here, we report a new class of electrostatically assisted precursors containing microscopic charged particles. This precursor manifests itself as the late stage of forced-spreading of a macroscopic dielectric film subjected to a unipolar ionic bombardment in a gas containing particulates. We put a model forward to predict dynamic behaviour of this electrostatic precursor dynamics. The spreading of the precursor film is predicted to be proportional to the square root of exposure time, which is consistent with the ellipsometric measurements. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M12.00006: Detachment of Sessile Droplets in Immiscible Fluids Using Electrowetting Jiwoo Hong, Sang Joon Lee The detachment (or removal) of droplets from a solid surface is an indispensable process in numerous practical applications. Here we firstly detach sessile droplets in immiscible fluids from a hydrophobic surface by electrowetting. The critical conditions for droplet detachment are determined by exploring the retracting dynamics for a wide range of driving voltages and physical properties of fluids. The relationships between physical parameters and dynamic characteristics of retracting and jumping droplets, such as contact time and jumping height, are also established. The threshold voltage for droplet detachment in oil with high viscosity is largely reduced by electrowetting actuations with a square pulse. Finally, by using DC and AC electrowetting actuations, we demonstrate the detachment of oil droplets with very low contact angle on a hydrophobic surface in water. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M12.00007: Inclusion of fluid-solid interaction in Volume of Fluid to simulate spreading and dewetting for large contact angles Kyle Mahady, Shahriar Afkhami, Lou Kondic The van der Waals (vdW) interaction between molecules is of fundamental importance in determining the behavior of three phase systems in fluid mechanics. This interaction gives rise to interfacial energies, and thus the contact angle for a droplet on a solid surface, and additionally leads to instability of very thin liquid films. We develop a hybrid method for including a Lennard-Jones type vdW interaction in a finite volume, Volume of Fluid (VoF) based solver for the full two-phase Navier-Stokes equations. This method includes the full interaction between each fluid phase and the solid substrate via a finite-volume approximation of the vdW body force. Our work is distinguished from conventional VoF based implementations in that the contact angle arises from simulation of the underlying physics, as well as successfully treating vdW induced film rupture. At the same time, it avoids the simplifications of calculations based on disjoining-pressure, where the vdW interaction is included as a pressure jump across the interface which is derived under the assumption of a flat film. This is especially relevant in the simulation of nanoscale film ruptures involving large contact angles, which have been studied recently in the context of bottom-up nanoparticle fabrication. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M12.00008: Exact solutions for contact lines on a soft substrate with uniform surface tension Laurent Limat, Julien Dervaux We have found an analytical solution describing the deformations of a soft substrate with uniform surface tension loaded by a straight contact line. Starting from the exact solution of this Flamant-Cerruti problem, we have extended our solution to contact lines with finite microscopic width, and to the case of a liquid strip between two straight contact lines (a 2D rivulet). These solutions are close to the approximate logarithmic ones proposed by one of us [1], except when two length scales of the problem are not separated. We discuss the liquid/solid force transmission, and the double transition of Lubbers et al [3], when two contact lines at finite distance are deforming a material with increasing softness. We provide analytical expressions for substrate distortion, as a function of the three length scales involved: distance between contact lines, microscopic scale, and elastocapillary length. Finally we discuss the selection of apparent contact angle, the possible extension to circular contact lines and the comparison with available experiments. \\[4pt] [1] L. Limat, EPJ-E Soft Matter 35, 134 (2012).\\[0pt] [2] L. A. Lubbers, J.H. Weijs, L. Botto, S. Das, B. Andreotti and J.H. Snoeijer, J. Fluid Mech. 747, R1 (2014). [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M12.00009: Role of contact line evaporation on the spreading of viscous droplet Wassim Bou-Zeid, David Brutin The effect of relative humidity and viscosity on the spreading dynamics of water-glycerol mixtures was analyzed for a range of relative humidities from 20{\%} to 80{\%}. Droplets of identical volume were deposited on ultra-clean microscope glass substrates. We demonstrated that, in addition to the competition between viscous forces, capillary forces and disjoining pressure, droplet spreading was also affected by the evaporation that occurred at the triple line. We provide an updated Tanner's law, which was modified to take into account the evaporative contribution. The same mechanism can be applied to adjust any fluid to Tanner's coefficient of 1/10. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M12.00010: Tailoring concentration gradients in microfluidic networks Cyprien Guermonprez, Charles Baroud, Sebastien Michelin We aim to produce precise concentration gradients in a microfluidic device in order to generate large number of droplets with a wide range of solute concentration. A method to study the distribution of a diffusing species in a highly parallel microfluidic network is proposed exploiting the spatial distribution of hydrodynamic resistances within the network. Starting from two co-flowing streams, the main channel supplies 10 to 64 side branches connected to a single outlet channel. Experiments and theoretical analysis are carried out for low Reynolds numbers and moderate to high P\'eclet numbers. The distribution of flow rates within the network is determined from its geometry and the distribution of hydrodynamic resistances and show maximum flow rates through the first and the last branches. Once the velocity distribution is known, a finite-difference method is used to predict the diffusion of a dichlorophenolindophenol solution in pure water. Both experimental and numerical results yield a variety of concentration distribution profiles that range from nearly uniform (small $P_e$) to linear and sigmoidal profiles (larger $P_e$). A good understanding of the underlying hydrodynamics enables the design of devices that generate rapidly precise chemical gradients. [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