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 H15: Drops: Elastic Surfaces and Fibers |
Hide Abstracts |
Chair: Paul H. Steen, Cornell University Room: 3022/3024 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H15.00001: Elastocapilllarity in insect adhesion: the case of beetle adhesive hair Sophie Gernay, Tristan Gilet, Pierre Lambert, Walter Federle The feet of many insects are covered with dense arrays of hair-like structures called setae. Liquid capillary bridges at the tip of these micrometric structures are responsible for the controlled adhesion of the insect on a large variety of substrates. The resulting adhesion force can exceed several times the body weight of the insect. The high aspect-ratio of setae suggests that flexibility is a key ingredient in this capillary-based adhesion mechanism. There is indeed a strong coupling between their elastic deformation and the shape of the liquid meniscus. In this experimental work, we observe and quantify the local deflection of dock beetle seta tips under perpendicular loading using interference microscopy. Our results are then interpreted in the light of an analytic model of elastocapillarity. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H15.00002: Capillary stretching of elastic fibers Suzie Protiere, Howard A. Stone, Camille Duprat Fibrous media consisting of constrained flexible fibers can be found in many engineered systems (membranes in filters, woven textile, matted paper). When such materials interact with a liquid, the presence of liquid/air interfaces induces capillary forces that deform the fibers. To model this interaction we study the behaviour of a finite volume of liquid deposited on two parallel flexible fibers clamped at both ends. A tension along the fibers is imposed and may be varied. We show that the system undergoes various morphological changes as the interfiber distance, the elasticity and the tension of the fibers are varied. For a certain range of parameters, the liquid spreads along the fibers and pulls them together, leading to the ``zipping'' of the fibers. This capillary adhesion can then be enhanced or reduced by changing the tension within the fibers. We will show that balancing stretching and capillary forces allows the prediction of this transition as well as the conditions for which detachment of the fibers occurs. These results may be used to prevent the clogging of fibrous membranes or to optimize the capture of liquids. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H15.00003: Tunable Transport of Drops on a Vibrating Fiber Alison Bick, Alban Sauret, Francois Boulogne, Howard Stone Transport of liquid drops on a fibrous medium is common in engineering systems such as fog harvesting and textile cleaning. The control of the drop movement on fibrous media can make these engineering systems more efficient. We investigated how to move drops along a single inclined fiber by controlling fiber vibration. Drop motion: static, sliding or falling, depends on the fiber inclination angle, drop volume, and the distance of the drop from the vibrating source. Specifically, by vibrating the fiber the transition between the three drop motion states can be controlled. By defining the response of drop movement to vibration frequency, we can model the drop movement transition. This knowledge is directly useful for controlling drop movement on the fiber. In particular, we experimentally demonstrated that vibration frequency can be used to transport a drop along a fiber. [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H15.00004: Compound droplet manipulations on fiber arrays Floriane Weyer, Marjorie Lismont, Laurent Dreesen, Nicolas Vandewalle Recent works demonstrated that fibers are the basis of an open digital microfluidics. Indeed, various processes such as droplet motion, fragmentation, trapping, releasing, mixing and encapsulation can be constructed on fiber arrays. However, addressing a large number of tiny droplets resulting from the mixing of several liquid components is still a challenge. Here we show that it is possible to manipulate tiny droplets reaching a high level of complexity. Wetting droplets are known to glide along vertical fibers. When a droplet reaches an horizontal fiber, it sticks at the crossing if capillary overcomes gravity. Otherwise, the droplet continues its way, crosses the node and leaves a tiny residue. Therefore, a vertical fiber decorated with a series of horizontal fibers will retain residual droplets at the successive nodes. An oil droplet, sliding on the vertical fiber, is able to collect the residues. Thus a multicompound droplet is created. The volume of the residual droplets has been studied and seems to be related to the diameters of both vertical and horizontal fibers. Moreover, the conditions under which the residues are released have been investigated in order to understand the formation of such a fluidic object. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H15.00005: Dynamic Contact Angle of a Soft Solid Stefan Karpitschka, Siddhartha Das, Bruno Andreotti, Jacco Snoeijer The wetting motion of a liquid on a rigid solid is a multi-scale problem in which viscous effects at microscopic scales modify the macroscopic liquid contact angle. Here we show that a contact line moving on a soft elastic substrate also leads to a dynamic contact angle, but this time, in the solid: the initially flat solid surface is deformed elastically into a sharp ridge whose angle depends on the contact line velocity. We predict the dynamic solid contact angle for generic viscoelastic rheologies. The solid angle provides a mechanism for changing the liquid contact angle, which is corroborated by dynamic wetting experiments of water on silicone gels. Our dynamical theory for soft wetting also captures the growth or decay of the wetting ridge, as recently accessed experimentally. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H15.00006: Dynamic wetting on soft substrates studied by x-ray imaging Su Ji Park, Jung Ho Je When a droplet sits on a soft surface, the surface tension of the droplet deforms the underlying material, creating a wetting ridge. Wetting ridge formation affects not only static wetting but also dynamic wetting behaviors. However, the underlying mechanisms are still largely unexplored mostly due to limitations in observation. Here, we directly visualize wetting ridges in real-time during spreading of a liquid drop using x-ray microscopy with high spatial and temporal resolutions. We clearly show that ridge-growth dynamics is closely linked to spreading behaviors. Interestingly, we reveal that the bending of a ridge cusp enhances the pinning force. We believe that our results would shed light on understanding of dynamic wetting behaviors on soft solids (e.g. contact angle hysteresis or evaporation) and be potentially important to interpret complex biological processes on or in soft tissues (e.g. cell-substrate interactions). [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H15.00007: Receding Contact Line on a Soft Gel: Dip-Coating Geometry Investigation Tadashi Kajiya, Philippe Brunet, Laurent Royon, Adrian Daerr, Mathieu Receveur, Laurent Limat We investigated the behavior of a liquid contact line receding on a soft gel surface (SBS-paraffin). To realize a well-defined geometry with an accurate control of velocity, a dip-coating setup was implemented. As the elastic modulus of the gel is small enough, a significant deformation takes place near the contact-line, which in turn influences the wetting behaviour. Depending on the translation velocity, the contact line exhibits different regimes of motions. Continuous motions are observed at high and low velocities, meanwhile two types of stick-slip motions, periodic and erratic, appear at intermediate velocities. We conjecture that the observed transitions could be explained in terms of the competition between different frequencies, i.e., the frequency $f$ of the strain field variation induced by the contact line motion and the frequency $f_{cross} = 1/\tau_{gel}$ related to the material relaxation. Finally, we propose a qualitative modeling which predicts the existing range of the stick-slip regimes. Therein, we consider the continuous spectrum associated with the surface deformation that ranges from the meniscus size to the elasto-capillary length: $1/l_{cap} < 1/l < 1/l_{e}$. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H15.00008: Wrapping a liquid drop with a thin elastic sheet Joseph Paulsen, Vincent D\'emery, Benny Davidovitch, Chris Santangelo, Thomas Russell, Narayanan Menon We study the wrapping of a liquid drop by an initially-planar ultrathin ($\sim 100$ nm) circular sheet. These elastic sheets can completely relax compressive stresses by forming wrinkles [1]. In the experiment, we find that when a small fraction of the drop is covered, the overall shape of the sheet (i.e. averaging over the wrinkles) is axisymmetric. As we shrink the drop further, the sheet develops radial folds that break the axisymmetry of the sheet and the drop. Our data are consistent with a model where the sheet selects the shape that minimizes the exposed liquid surface area. We thus identify a ``geometric wrapping'' regime, where the partially-wrapped shape depends only on the relative radii of the sheet and the drop; the global breaking of axisymmetry is independent of the elastic energy of the deformed sheet. This regime requires that bending energy is negligible compared to surface energy, in contrast to the ``capillary origami'' regime [2] where the static shape of the drop comes from a balance of bending and capillary forces.\\[4pt] [1] King et al., PNAS 109, 2012.\\[0pt] [2] Py et al., PRL 98, 2007. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H15.00009: Dynamics of fluid driven fracturing of magnetic elastica Jerome Neufeld, Thomas Le Reun The dynamic spreading of viscous fluids between magnetic elastic sheets provides an novel experimental system in which to examine the interplay between bending, in-plane tension, and a form of ``magnetic'' fracturing. A suite of constant volume, and fixed flux injections of viscous fluid demonstrate the quasi-static and dynamic responses of the magnetic, elastic sheets. For fixed fluid volume, magnetic adhesion leads to static solutions in both the tensional (thin membrane) and bending (thick membrane) limits, directly analogous to to the sessile capillary drop. These static tensional and bending solutions are also observed when the fluid injection flux is small. For larger fluid fluxes, new dynamic solutions emerge as reflected in the rates of deformation and spreading. This new experimental system provides a laboratory in which to repeatably study the dynamics of fluid driven fracturing of elastica. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H15.00010: Elastic membrane for needle-free drop deposition Prashant Waghamre, Sushanta Mitra Contact angle measurements on low-energy surfaces (like superhydrophobic, etc.) are often a challenge as the needle-drop-surface combination does not allow to detach the drop readily. Here we present a new technique to achieve a ``needle-free'' drop by bringing the drop in contact with an elastic membrane, kept between the needle-drop assembly and the characterizing substrate. The detachment of the drop from the needle is achieved by retracting the needle-drop assembly at a finite speed and allowing the drop to receive the elastic energy of the soft flexible membrane. Such interaction of the drop with the elastic membrane permits the drop to get repelled from the elastic membrane and gets deposited on a characterizing substrate. The repelling behavior of the drop can be controlled by appropriately selecting the mechanical and wetting properties of the elastic membrane. This technique not only provides a needle-free drop deposition that is independent of the physical properties of the liquid and the needle but it also allows achieving the drop size that is independent of the needle diameter. [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