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 M2: Surface Tension Effects: Textured Substrates |
Hide Abstracts |
Chair: Jonathan P. Rothstein, University of Massachusetts Room: 3002 |
Tuesday, November 25, 2014 8:00AM - 8:13AM |
M2.00001: Capillary trapping on a rough surface Jason Wexler, Ian Jacobi, Melissa Chow, Howard Stone Recent research has shown that rough or patterned surfaces infused with a lubricating liquid can display superhydrophobic properties. However, if such a surface is exposed to external flow, the shear induced by the outer fluid can drain the lubricating layer, causing regions of the surface to transition to a hydrophilic Wenzel state. In addition, the high specific gravity of lubricating liquids means that this loss can be driven by gravity alone, in the absence of flow. We examine the shear- and gravity-driven failure modes of liquid-infused patterned surfaces experimentally, and develop a unified model to predict the dynamics of drainage via these two types of forcing. We find that the dynamic evolution of the two drainage mechanisms takes on a single functional form. Under the influence of gravity, we show that a finite length of the surface will remain filled indefinitely; this is a variant of the familiar capillary rise height. Under the influence of external shear, the steady-state liquid retention depends on the outer flow velocity field. [Preview Abstract] |
Tuesday, November 25, 2014 8:13AM - 8:26AM |
M2.00002: In situ observations of wetting transition on submerged microstructured hydrophobic surfaces Pengyu Lv, Yahui Xue, Hao Lin, Huiling Duan Superhydrophobicity of microstructured surfaces has a promising application in drag reduction. The air pockets trapped in the microstructures play the key role. However, the wetting transition from Cassie to Wenzel state will spontaneously take place due to air diffusion into the water around under pressurization, leading to the loss of air pockets and the failure of superhydrophobicity. The current work examines in situ liquid-air interfaces on a submerged surface patterned with cylindrical micropores using confocal microscopy. The dynamic process of wetting transition are directly observed and measured quantitatively, and the data are in good agreement with a diffusion-based model prediction. A similarity law along with a characteristic time scale is derived, which governs the lifetime of the air pockets. Moreover, two kinds of collapses of the menisci in the final stage of transition which refer to the symmetric and asymmetric collapses are also captured. A strategy of hierarchical structures is proposed to avoid the loss of stability of the liquid-air interfaces in advance due to asymmetric collapse. The present work enables a better prediction of underwater superhydrophobicity, and benefits design explorations to enhance its longevity. [Preview Abstract] |
Tuesday, November 25, 2014 8:26AM - 8:39AM |
M2.00003: Force of Adhesion upon loss of Contact Angle Hysteresis: when a Liquid behaves like a Solid Juan Escobar, Rolando Castillo Liquids and solids are in general expected to behave very differently in their contact with a solid surface. While that the mechanical deformation of an elastic solid sphere is perfectly reversible, a liquid drop normally deforms in an irreversible way. Nevertheless, a liquid drop in contact with a perfectly-solvophobic surface should also deform reversibly, giving rise to loss of contact angle hysteresis. In this work,\footnote{Escobar J.V. and Castillo R., Phys. Rev. Lett., 111, 22, 226102, (2013)} the theoretically predicted vanishment of the macroscopic contact angle hysteresis is found experimentally along with a small but finite force of adhesion 0.55 $\mu$N that, unexpectedly, is independent of the history of the preload. These results are obtained with a novel Capillary Force Microscope. Our results agree with the prediction of a model in which the surface tension of the liquid provides the counterpart of the restoring force of an elastic solid, evidencing that the dewetting of a liquid in the absence of strong pinning points is equivalent to the detachment of an elastic solid. [Preview Abstract] |
Tuesday, November 25, 2014 8:39AM - 8:52AM |
M2.00004: Thermocapillary Driven Droplet Motion on Lubricant Impregnated Textured Surfaces Nada Bjelobrk, Henri-Louis Girard, Hyuk-Min Kwon, David Quere, Kripa K. Varanasi Here, we show that lubricant impregnated surfaces (LIS) promote thermocapillary induced motion of liquid droplets. The contact angle of a droplet on LIS is low, which increases the effective temperature gradient over the droplet. At the same time, the contact angle hysteresis is significantly decreased and thus the pinning is suppressed. The shear forces due to the thermocapillary effect at the free interface between the droplet and the lubricant can enhance the propulsion velocity by an order of magnitude. Hereby, two aspects are are supporting the propulsion: A lubricant/droplet pair should have a large and positive interfacial tension gradient. The lubricant should also fully encapsulate the substrate. We compare various lubricant viscosities and droplet sizes to examine the thermocapillary effect and propose a model to predict the velocity of droplets moving on LIS on a temperature gradient. [Preview Abstract] |
Tuesday, November 25, 2014 8:52AM - 9:05AM |
M2.00005: Nanostructured surfaces and the dynamics of colloidal particles, droplets, and slugs Carlos Colosqui, Joel Koplik, Jeffrey Morris, Antonio Checco Nanoscale heterogeneities in physical and/or chemical surface properties can have major consequences in the dynamics of colloidal particles at a liquid-fluid interface or femto/picoliter droplets and slugs on a solid substrate. For example, nanoscale heterogeneities can lead to crossovers from fast exponential to slow logarithmic adsorption of colloidal particles at interfaces or membranes, as well as self-propelled motion of microdroplets and slugs on nanopatterned substrates or capillaries. Theoretical models based on continuum thermodynamics can be extended to describe these phenomena at the colloidal scale, while molecular dynamics simulations can assist by providing critical insights into the coupling between thermal fluctuations, interfacial forces, and hydrodynamics at the nanoscale. This talk will present recent theoretical, numerical, and experimental results that (i) document transitions between different dynamic regimes, and (ii) establish relations between physical parameters and characteristic scales in the dynamics of colloidal particles, microdroplets, and slugs induced by nanoscale surface heterogeneities. [Preview Abstract] |
Tuesday, November 25, 2014 9:05AM - 9:18AM |
M2.00006: Elastocapillary assembly of silver nanotube forest Xin Yang, Min Pack, Ying Sun Nanorods/nanotubes have large surface areas making them promising for applications such as high-performance battery and capacitor electrodes, photovoltaics, and interconnects. In this study, we demonstrate the formation of 3D microarchitectures via elastocapillary self-assembly of silver nanotube forests. Patterned silver nanotube forests of different lengths and diameters are made by inkjet printing of silver nanoinks into nanoporous anodic aluminum oxide membranes. These silver nanotube forests are then self-assembled into ordered microstructures via capillary forces induced by liquid condensation, which is compared with immersing nanotubes directly into a liquid. The effects of length, diameter, and footprint of the nanotube forest on self-assembled patterns are systematically studied. By decreasing the footprint and/or increasing the length of nanotube forest, the stiffness of the nanotube forest decreases, bringing the nanotubes together to form closely packed microstructures. [Preview Abstract] |
Tuesday, November 25, 2014 9:18AM - 9:31AM |
M2.00007: Programming self assembly by designing the 3D shape of floating objects Martin Poty, Guillaume Lagubeau, Geoffroy Lumay, Nicolas Vandewalle Self-assembly of floating particles driven by capillary forces at some liquid-air interface leads to the formation of two-dimensionnal structures. Using a 3d printer, milimeter scale objets are produced. Their 3d shape is chosen in order to create capillary multipoles. The capillary interactions between these components can be either attractive or repulsive depending on the interface local deformations along the liquid-air interface. In order to understand how the shape of an object deforms the interface, we developed an original profilometry method. The measurements show that specific structures can be programmed by selecting the 3d branched shapes. [Preview Abstract] |
Tuesday, November 25, 2014 9:31AM - 9:44AM |
M2.00008: Discrete and continuum dynamics of elastocapillary coalescence of plates and pillars Zhiyan Wei, T. Schnieder, J. Kim, H.-Y. Kim, J. Aizenberg, L. Mahadevan When a fluid-immersed array of lamellae or filaments that is attached to a substrate is dried, evaporation leads to the formation of menisci on the tips of the plates or pillars that bring them together. Building on prior experimental observations, we use a combination of theory and computation to understand the nature of this instability and its evolution in both the two-dimensional and three-dimensional setting of the problem. For the case of lamellae, we derive the interaction torques based on the relevant physical parameters, predict the critical volume of the liquid and the 2-plate-collapse eigenmode at the onset of instability, and use numerical simulations to explain the hierarchical cluster formation and characterize the sensitive dependence of the final structures on the initial perturbations. We also characterize these at a continuum level by partial differential equations. We then generalize our analysis to treat the problem of pillar collapse in 3D, where the fluid domain is completely connected. [Preview Abstract] |
Tuesday, November 25, 2014 9:44AM - 9:57AM |
M2.00009: Interfacial transport and orientation of Janus nanoparticles under shear flow Hossein Rezvantalab, Shahab Shojaei-Zadeh We investigate the configuration of Janus nanoparticles adsorbed at liquid-fluid interfaces in presence of shear flow. The interfacial behavior of nanoparticles with different size and shape is followed using Molecular Dynamics simulations. We create Janus nanoparticles by tuning the affinity of the atoms on each side of the particle with the two fluids, and model the shear as a symmetric Couette flow. We demonstrate the existence of a steady-state orientation for particles at the interface, which is governed by the balance between the shear-induced torque and the resistance due to capillary forces. There is a threshold shear rate above which the nanoparticle starts to rotate out of its energetically favorable upright orientation. This threshold is found to to be higher for more amphiphilic particles due to the stronger interfacial tension resisting against the shear-induced disturbance. Moreover, the geometry plays a significant role in defining the range of attainable orientations. Janus cylinders with high aspect ratio show a sudden shift in orientation which does not drastically change with increasing shear rate, while thin discs require a larger threshold shear but can achieve a wider range of orientations. Our analysis of a fluid flow that reorients suspended nanoparticles can also give insight into the hemodynamics of blood flow and the interaction of anisotropic drug carriers with cell membranes. [Preview Abstract] |
Tuesday, November 25, 2014 9:57AM - 10:10AM |
M2.00010: The dynamics and breakup of water streams flowing down an inclined superhydrophobic surface Jonathan Rothstein, Elizabeth Baumhoff In this talk, we present a series of experiments investigating the flow of water streams down a series of hydrophobic and superhydrophobic surfaces. To create the superhydrophobic surfaces, random texture was imparted onto a Teflon surface by sanding it with sand papers with a range of grit sizes. Our previous work has showed that there exists an optimal sand paper grit (240 grit) for eliminating contact angle hysteresis and reducing drag. The effect of advancing contact angle, contact angle hysteresis, plate inclination and flow rate on the shape of the meandering streams of water will be presented. We will show that the dynamics and breakup of water streams flowing down superhydrophobic surfaces is strongly dependent on contact angle hysteresis. We will show that decreasing the contact angle hysteresis makes the rivulets less stable resulting in an increased number of bends, more side-to-side motion of the stream and a reduction in the length of the stream at the moment it breaks up into drops. Additionally, decreasing hysteresis also results in a reduction in the radius of curvature of the bends observed along the meandering stream. Finally, we will show that at high flow rates, ejection of an intact liquid stream from the superhydrophobic surface can be observed. [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