Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M11: Surface Tension III |
Hide Abstracts |
Chair: Camille Duprat, Princeton University Room: 314 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M11.00001: Autophobing on a liquid substrate Ellen Peterson, Stephen Garoff, Roomi Kalita, Ramankur Sharma When a drop of fluid is deposited on another fluid it may either completely spread over the underlying fluid or it may reach an equilibrium shape, assuming the two fluids are immiscible. The choice of end state is predicted by the sign of the spreading coefficient ($S=\Sigma^F-\Sigma^D-\Sigma^{DF}$) which relates the surface tension of the three interfaces: fluid/air ($\Sigma^F$), drop/air ($\Sigma^D$), and drop/fluid ($\Sigma^{DF}$). We experimentally investigate this behavior but discover that a static lens may form even when the spreading coefficient predicts complete spreading. We measure the surface tension of the underlying fluid and deduce that fluid escapes the contact line of the drop. If we allow the surface tension of the subphase to change due to this escaping fluid, we find the resulting spreading coefficient predicts a static lens. We compare the results to a mathematical model and confirm the observed spread area. The results of this investigation suggest that the lens resists flowing over the escaped layer of the same fluid, the mechanism of autophobing. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M11.00002: In situ, noninvasive characterization of superhydrophobic coatings G.C. Tepper, M.A. Samaha, H. Vahedi Tafreshi, M. Gad-el-Hak Light scattering was used to measure the time-dependent loss of air entrapped within a submerged microporous hydrophobic surface subjected to different environmental conditions. The loss of trapped air resulted in a measurable decrease in surface reflectivity and the kinetics of the process was determined in real time and compared to surface properties, such as porosity and morphology. The light-scattering results were compared with measurements of skin-friction drag, static contact angle, and contact-angle hysteresis. The {\em In situ}, noninvasive optical technique was shown to correlate well with the more conventional methods for quantifying surface hydrophobicity, such as flow slip and contact angle. {\em In situ} characterization of submerged hydrophobic surfaces using light scattering represents a new and useful tool for real-time estimation of hydrophobicity and drag reduction. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M11.00003: Salinity Effects on Superhydrophobic Coatings F.O. Ochanda, M.A. Samaha, H. Vahedi Tafreshi, G.C. Tepper, M. Gad-el-Hak Experiments are carried out to investigate the effect of NaCl concentrations on degree of hydrophobicity and longevity of polystyrene fibrous coating. A rheological study using salt water as a test fluid is performed to observe the generated drag reduction from the coating with increasing salt concentration compared to deionized water. Contact-angle measurements of droplets of solutions on the surface are used to validate the results from the rheometer. In situ noninvasive optical spectroscopy system is used to measure the time-dependent loss of entrapped air within the submerged fibrous coating. water for comparison. The superhydrophobic coating used is made of polystyrene fibers that are deposited using DC-biased AC-electrospinning. Such fabrication methods are far less expensive than ordered-microstructured fabrications, bringing the technology closer to large-scale submerged bodies such as submarines and ships. The present study sheds some light on how properties of a superhydrophobic coating could be influenced by water salinity. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M11.00004: Modeling superhydrophobic surfaces comprised of random roughness M.A. Samaha, H. Vahedi Tafreshi, M. Gad-el-Hak We model the performance of superhydrophobic surfaces comprised of randomly distributed roughness that resembles natural surfaces, or those produced via random deposition of hydrophobic particles. Such a fabrication method is far less expensive than ordered-microstructured fabrication. The present numerical simulations are aimed at improving our understanding of the drag reduction effect and the stability of the air--water interface in terms of the microstructure parameters. For comparison and validation, we have also simulated the flow over superhydrophobic surfaces made up of aligned or staggered microposts for channel flows as well as streamwise or spanwise ridge configurations for pipe flows. The present results are compared with other theoretical and experimental studies. The numerical simulations indicate that the random distribution of surface roughness has a favorable effect on drag reduction, as long as the gas fraction is kept the same. The stability of the meniscus, however, is strongly influenced by the average spacing between the roughness peaks, which needs to be carefully examined before a surface can be recommended for fabrication. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M11.00005: Spreading of thin rotating films: Competition of thermal Marangoni, centrifugal, and gravitational forcing Joshua Dijksman, Shomeek Mukhopadhyay, Robert Behringer We experimentally probe the quasi static spreading of a sessile drop on a substrate under the influence of competing gravitational, thermo capillary (Marangoni) and centrifugal forcing. We use silicone oil on a prewetted silicon wafer, and we employ an interferometric technique to study the evolution of the film height profile. We discuss our results in the context of recent theory developed by Bostwick et al. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M11.00006: On integrable singularities and apparent contact angles within a classical paradigm: partial and complete wetting regimes with or without phase change Pierre Colinet, Alexey Rednikov Far from claiming any ultimate resolution of the contact line paradoxes, we argue that a somewhat controversial paradigm, originally employed by de Gennes and collaborators, actually appears both to be quite reasonable at its foundations and to lead to physically consistent final results in a wide variety of situations. Curiously enough, while containing a singularity in itself, the approach nonetheless renders the classical contact-line singularities -- both hydrodynamic and thermal -- integrable, in particular as far as several quantities of interest are concerned. It is also readily applicable to quite a few situations: from equilibrium shapes and moving contact lines of a non-volatile liquid, to cases with evaporation into either a pure-vapor or an inert-gas atmosphere. The paradigm actually consists in an approach involving both the (positive or negative) spreading coefficient and the disjoining pressure in the form of a positive inverse cubic law, a conceptual framework that most notably describes structures with truncated precursor films on a macroscopically bare solid surface. [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M11.00007: On possible resolutions of the micro-edge problem for a contact line moving on a solid in a pure-vapor atmosphere with no slip and without extended precursor films Alexey Rednikov, Pierre Colinet At the previous APS/DFD meeting, we reported on the possibility of a singularity-free description of a moving contact line totally in the framework of classical physics (no disjoining pressure, no slip) thanks to the phase change whose intensity is regulated by Kelvin effect. Pushing this idea further, there remains a related more practical issue: the Kelvin effect, even though classical, becomes apparent at such small scales that the disjoining pressure (DP) may nonetheless play a significant role. Here we show, for a class of DP isotherms remaining finite at zero film thicknesses, that the same kind of natural singularity-resolution mechanism still holds. As before, we consider, in the framework of the lubrication theory and a classical one-sided model, a contact line moving at a constant velocity (advancing or receding) and starting abruptly at a (formally) bare solid surface, the micro- contact angle being either equal to zero or finite. Also touched upon is a possible resolution of the remaining integrable singularities within the paradigm of de Gennes and coworkers, considered here in another talk by the present authors, by means of regularizing the DP isotherm at very small thicknesses. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M11.00008: Impregnation transition in a powder Pascal Raux, Heloise Cockenpot, David Quere, Christophe Clanet When an initially dry pile of micrometrical grains comes into contact with a liquid, one can observe different behaviors, function of the wetting properties. If the contact angle with the solid is low, the liquid will invade the pile (impregnation), while for higher contact angles, the grains will stay dry. We present an experimental study of this phenomenon: a dry pile of glass beads is deposed on the liquid surface, and we vary the contact angle of the liquid on the grains. We report a critical contact angle below which impregnation always occurs, and develop a model to explain its value. Different parameters modifying this critical contact angle are also investigated. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M11.00009: Sweating Liquid Micro-Marbles: Drop wise condensation on hydrophobic particulate materials Mahesh Panchagnula, Prasad Bhosale Liquid marbles have been presented as important candidates in such important applications as gas sensing and bulk liquid transport since they were first proposed. In the current study, we present a remarkably simple self-assembly process driven by condensation on a nanoparticulate matrix giving rise to nearly monodisperse liquid marbles whose sizes can be controlled in the range of diameters from 2$\mu $m to 1000$\mu $m, monodisperse within a few micrometers in distribution width. We show that the primary mechanism causing the formation of liquid marbles is droplet nucleation followed by growth driven by condensation. Drop coalescence in dense droplet ensembles is the secondary mechanism, which attempts to destroy the distribution width controllability. It will also be demonstrated that coalescence dominated growth gives rise to a hitherto unreported growth law owing to the extremely high degree of mobility of embedded liquid marbles. Through a combination of understanding derived from these two physical processes, it will be shown that the proposed process provides control over both the mean marble diameter as well as the marble size distribution. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M11.00010: DNS of thermocapillary flows based on two-scalar temperature representation Dieter Bothe, Chen Ma The direct numerical simulation (DNS) of thermocapillary two-phase flow with free deformable interface requires the solution of the two-phase Navier-Stokes equations in 3D together with the energy balance. We employ the sharp interface model which is solved using an extended volume of fluid method, where the discretization is based on Finite Volumes. The energy equation is given in temperature form, where the temperature field is represented by two scalars, one for each phase. This way the averaging over grid cells is confined to the individual phases and, hence, a smearing of the temperature gradient jump is avoided. Interpolation of the temperature within interfacial cells, exploiting the energy transmission condition, yields accurate temperatures at the interface, which is of utmost importance for the calculation of thermocapillary forces. Here the position and orientation of the interface is approximated by piecewise linear interface construction (PLIC). This method is applied to investigate liquid films on locally heated planar, respectively heated structured substrates. The approach allows for the numerical simulation of evaporating flows coupled with thermal Marangoni effects. [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