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 A13: Drops: Levitation and Superhydrophobic Surfaces |
Hide Abstracts |
Chair: Konrad Rykaczewski, MIT Room: 3020 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A13.00001: Surfing a magnetic wave Eline Dehandschoewercker, David Quere, Christophe Clanet Surfing is a free surface sport in which the athlete rides a wave standing on a board. However, any object plunged into the water or put on its surface is not always captured by an approaching wave, just like the classic example of a fisching float. So, a particle can be captured or not by a wave. Two regimes are defined : surf (captured) and drift (not captured). We focus on the question of the transition between these two regimes. Here we address the question with a magnetic wave. We have developed an experimental setup which allows the control of all relevant physical parameters. Liquid oxygen, which is paramagnetic and undergoes Leidenfrost effect, can be used to ensure magnetic and frictionless particles. A permanent magnet in translatory movement allows us to create a definite magnetic wave. We discuss the motion of oxygen drops deposited on an smooth and horizontal surface above an approaching magnet. First we show the existence of a critical speed below which drops are captured and determine how it depends on the velocity and intensity of the magnetic wave. Then we experimentally investigate the parameters that would affect the movement of drops in each regime. Finally, models have been developed to interpret magnetic drops motion and guarantee an efficient control. [Preview Abstract] |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A13.00002: Acoustical radiation torque and force for spheres and Bessel beam extinction efficiency Philip L. Marston, Likun Zhang The scattering of optical and acoustical beams is relevant to the levitation and manipulation of drops. Here we examine theoretical developments in the acoustical case. We previously showed how the optical theorem for extinction can be extended to invariant beams. The example of a sphere in a Bessel beam facilitates the direct comparison with a circular disc computed using Babinet's principle and the Kirchhoff approximation (P. L. Marston, J. Acoust. Soc. Am. 135, 1668-71 (2014)). In related work, by considering traveling or standing wave first-order vortex beams we previously showed that the radiation torque is the ratio of the absorbed power and the radian acoustic frequency (L. Zhang and P. L. Marston, Phys. Rev. E. 84, 065601 (2011)). By modifying the scattering to account for the viscosity of the surrounding fluid in the analysis of the absorbed power, approximations for radiation torque and force are obtained at long wavelengths in special cases (P. L. Marston, Proc. Meetings on Acoustics 19, 045005 (2013)) and these can be compared with results published elsewhere. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A13.00003: The performance and operating mechanism of the ultrasonic scrubber J.R. Saylor, W. Ran An ultrasonic standing wave field is commonly used to levitate drops, facilitating drop studies in several ways. In the typical use of such a standing wave field, drops are simply placed at the node of the field and thereby levitated. However, it is also true that any particles or drops located in the general vicinity of the nodes of an ultrasonic standing wave are drawn toward the nodes where they accrue. We have shown that this effect can be used to create an ``ultrasonic scrubber", wherein the combination of a fine water mist and an ultrasonic standing wave field is used to remove particles (e.g. particulate pollutants) from a gas flow directed at the field ({\it Ran, Saylor, \& Holt, J. Aerosol Sci., 67, 104-118 (2014)}). In this talk details are presented of the operating mechanism responsible for the success of this approach to scrubbing. The results of an experimental study are also presented showing the effect of the gas flow rate and droplet size distribution on the scavenging coefficient for one version of the ultrasonic scrubber. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A13.00004: Levitation, Herringbones and Propulsion Helene de Maleprade, Dan Soto, Christophe Clanet, David Quere Controlling objects motion without contact is a major application issue as it ensures high mobility, low friction and no contamination. Levitation can be induced by blowing air from below through a porous medium, to create a thin air cushion under the object. The airflow is isotropic but if some asymmetry is introduced to rectify it, the levitating object can be controlled and propelled [1]. In our experiments, microscopic textures are engraved on the top of the porous medium, which directs the airflow. The resulting viscous entrainment enables drops, rigid plastic or even glass cards to self-propel [2]. If the micro-textures are displayed on the propelled object, the direction of the motion is reversed, which is found to result from a different mechanism of entrainment. \\[4pt] [1] Linke, H. et al, Self-Propelled Leidenfrost Droplets, Phys. Rev. Lett. 96, 2006\\[0pt] [2] Soto, D. and Lagubeau, G. and Clanet, C. and Quere, D. Surfing on a Herringbone, in prep., 2014 [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A13.00005: Free oscillations of a magnetic drop Eric Falcon, Timothee Jamin, Yacine Djama When a flattened drop of liquid is put on a substrate subjected to vertical vibrations, it undergoes a parametric instability above a critical acceleration. An azimuthal pattern occurs around the drop and oscillates at half the forcing frequency: a star-shaped drop is then observed made of several oscillating lobes. Here, we use a drop of ferrofluid, a magnetic liquid that responds to an external magnetic field. We report an experimental study of a ferrofluid drop on a superhydrophobic substrate vertically vibrated in presence of a weak vertical magnetic field of tunable amplitude. We find that the eigenmode frequencies of the drop are shifted by the magnetic field. We show that this shift is due to an interaction between the magnetic field and standing waves on the drop top. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A13.00006: Active surfaces: Ferrofluid-impregnated surfaces for active manipulation of droplets Karim Khalil, Seyed Reza Mahmoudi, Numan Abu-dheir, Kripa Varanasi Droplet manipulation and mobility on non-wetting surfaces is of practical importance for diverse applications ranging from micro-fluidic devices, anti-icing, dropwise condensation, and biomedical devices. The use of active external fields has been explored via electric, acoustic, and vibrational, yet moving highly conductive and viscous fluids remains a challenge. Magnetic fields have been used for droplet manipulation; however, usually, the fluid is functionalized to be magnetic, and requires enormous fields of superconducting magnets when transitioning to diamagnetic materials such as water. Here we present a class of active surfaces by stably impregnating active fluids such as ferrofluids into a textured surface. Droplets on such ferrofluid-impregnated surfaces have extremely low hysteresis and high mobility such that they can be propelled by applying relatively low magnetic fields. Our surface is able to manipulate a variety of materials including diamagnetic, conductive and highly viscous fluids, and additionally solid particles. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A13.00007: Visualization of Buoyant Convection in Droplets on Superhydrophobic Surfaces Susmita Dash, Aditya Chandramohan, Justin Weibel, Suresh Garimella We investigate hitherto unreported flow characteristics that are manifested inside a sessile droplet when evaporating on a superhydrophobic surface. Evaporative cooling at the droplet interface establishes a temperature gradient that induces buoyant convection inside the droplet. A single rotating vortex, with a solid body rotation flow pattern, is observed using Particle Image Velocimetry. This flow pattern develops due to the large height-to-diameter aspect ratio of the droplet, which dictates a stable buoyancy-induced convection mode with one rolling vortex. The flow velocity is an order of magnitude higher compared to droplets evaporating on hydrophobic substrates. The high recirculation velocity, combined with the sliding contact line of the droplet, mitigates deposition of particles on the substrate during the evaporation process and enables a single concentrated deposition after complete drying on superhydrophobic substrates. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A13.00008: Multifunctional polymer nano-composite based superhydrophobic surface Tanmoy Maitra, Ashish Asthana, Robert Buchel, Manish K. Tiwari, Dimos Poulikakos Superhydrophobic surfaces become desirable in plethora of applications in engineering fields, automobile industry, construction industries to name a few. Typical fabrication of superhydrophobic surface consists of two steps: first is to create rough morphology on the substrate of interest, followed by coating of low energy molecules. However, typical exception of the above fabrication technique would be direct coating of functional polymer nanocomposites on substrate where superhydrophobicity is needed. Also in this case, the use of different nanoparticles in the polymer matrix can be exploited to impart multi-functional properties to the superhydrophobic coatings. Herein, different carbon nanoparticles like graphene nanoplatelets (GNP), carbon nanotubes (CNT) and carbon black (CB) are used in fluropolymer matrix to prepare superhydrophobic coatings. The multi-functional properties of coatings are enhanced by combining two different carbon fillers in the matrix. The aforementioned superhydrophobic coatings have shown high electrical conductivity and excellent droplet meniscus impalement resistance. Simultaneous superhydrophobic and oleophillic character of the above coating is used to separate mineral oil and water through filtration of their mixture. [Preview Abstract] |
Sunday, November 23, 2014 9:44AM - 9:57AM |
A13.00009: Is micro-nano texture the only reason for under-water superoleophobicity of fish scale? Naga Siva Kumar Gunda, Prashant Waghmare, Sushanta Mitra There is a huge surge in developing liquid repellant surfaces based on the micro/nanostructures that are inherently present in nature, like the one in case of fish scales. Through systematic contact angle measurement of oil drops on fish scales submerged in souring water medium, we have demonstrated that the superhydrophobic/superoleophobic nature of fish scales is attributed to a combination of the mucus layer and the hierarchical structures. The mucus layer on the fish scales produces an unprecedented contact angle close to 180$^{\mathrm{o}}$ in contrast to the contact angle of 150$^{\mathrm{o}}$ produced in the absence of the mucus layer. We have also identified, through FTIR analysis, that the distinct chemical signatures of mucus accountable for such large contact angles. [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