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 M4: Drops IX: Spreading on Surfaces |
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Chair: Pirouz Kavehpur, University of California, Los Angeles Room: 307 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M4.00001: Spreading and wetting of impacting drops: Three-dimensional simulations using Conformal Decomposition Finite Elements Scott Roberts, Jeremy Lechman Understanding the spreading and wetting of liquid drops impacting a solid substrate is of interest to many industrial processes, including coating, printing, and thermal spray processes. Depending on the contact angle and wetting behavior, these drops can exhibit many shapes, including disks, crowns, and rebounding drops. Despite its importance, accurately capturing these dynamics using numerical simulations remains a daunting task. In this talk, we use a new Conformal Decomposition Finite Element Method (CDFEM), which seeks to capture the benefits of both moving-mesh and level-set methods, to study drop impact and spreading. Three-dimensional simulations are performed and interface profiles and drop spreading ratios are compared to previous experimental and theoretical studies. The strength of this method is also demonstrated in more complicated geometries, where three-dimensional simulations are necessary. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M4.00002: Slip in viscous contact-line movement Henrik van Lengerich, Paul Steen, Kenneth Breuer The typical continuum fluid dynamics formulation cannot be used to model the spreading of a liquid on a solid because a stress singularity prevents contact-line motion. It is well known that this situation can be remedied by introducing a slip. We perform Stokes-flow simulations with slip and compare these with experiments. In the experiment, liquid (squalane) is forced through two parallel sapphire plates (roughness 0.6nm), and the meniscus shape and its speed are measured. The slip-length for this liquid/solid pair has been measured previously in an independent experiment absent of contact lines (T. Schmatko et. al. PRL 94, 244501). The same geometry is used in a boundary integral method simulation, accurate to within a few molecular diameters in the vicinity of the contact-line. The slip-length in the simulations can be varied such that the meniscus shape matches the experiment. Preliminary results suggest this slip-length is an order of magnitude lower than that reported by Schmatko. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M4.00003: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M4.00004: Spreading and Arrest of Molten Liquid on Solid Substrates Faryar Tavakoli, Pirouz Kavehpour When a drop is placed on a solid surface with temperature below solidification temperature, it comes to arrest at a finite time after deposition. This problem has a wide range of applications in engineering such as coating, ink jets and 3D printers. In the last 10 years, there have been very few studies of this paramount phenomenon. The physical parameters of the liquid and the substrate as well as spreading speed affect the arrest radius, the contact angle at arrest point, and time of arrest. Here, we use several different fluids to study these properties on the outcome of the spreading dynamics. The fluid is deposited using a syringe pump system to provide a constant flow rate for deposition. The evolution of wetting contact angle and base diameter of spreading drops were measured by a high speed digital camera. A parametric study of the radius of arrest and the arrested contact angle is provided. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M4.00005: Drop dynamics on a thin film: Drop engulfment Pilnam Kim, Andreas Carlson, Howard A. Stone When a liquid drop spreads on a thin film of another immiscible liquid, the liquid drop and film deform to minimize the surface energy. We investigate the dynamics of the motion of a water drop that comes in contact with a thin film of a silicone oil. We first present the engulfment of a water drop by a silicone film. We identify that the drop engulfment is dominated by the drop size and is independent of the thin film thickness. The interface where water/oil/air meets deforms as a spreading event, where the radius evolves as a power-law in time. If the solid that supports the thin oil film is hydrophobic, the film between the drop and the solid remains stable even if it is thinned by gravity, making the drop ``float'' on the solid. In the presence of a gradient in solid surface energy, the floating water drop moves toward the parts of the solid surface that have the highest energy. We suggest that this motion is caused by the imbalance in surface forces at the front and rear of the droplet, where the driving force is believed to originate from the interface-solid substrate interaction and acts through the thin silicone film. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M4.00006: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M4.00007: Motion and shape of partially non-wetting drops on inclined surfaces Baburaj A Puthenveettil, Vijaya Senthilkumar K, E.J. Hopfinger We study high Reynolds number ($Re$) motion of partially non- wetting liquid drops on inclined surfaces using (i) water on Fluoro-Alkyl Silane (FAS) coated glass and (ii) mercury on glass. The high hysteresis ($35^\circ$) water drop experiments have been conducted for a range of inclination angles $26^\circ < \alpha < 62^\circ$ which give a range of Capillary numbers $0.0003 < Ca < 0.0075$ and $137 < Re < 3142$. For low hysteresis ($6^\circ$) mercury on glass experiments, $5.5^\circ < \alpha < 14.3^\circ$ so that $0.0002 < Ca < 0.0023$ and $3037 < Re < 20069$. It is shown that when $Re\gg 10^3$ for water and $Re\gg 19$ for mercury, the observed velocities are accounted for by a boundary layer flow model. The dimensionless velocity in the inertial regime, $Ca\sqrt{Re}$ scales as the modified Bond number ($Bo_m$), while $Ca\sim Bo_m$ at low $Re$. We show that even at high $Re$, the dynamic contact angles ($\theta_d$) depend only on $Ca$, similar to that in low $Re$ drops. Only the model by Shikhmurzaev is consistent with the variation of dynamic contact angles in both mercury and water drops. We show that the corner transition at the rear of the mercury drop occurs at a finite, receding contact angle, which is predicted by a wedge flow model that we propose. For water drops, there is a direct transition to a rivulet from the oval shape at a critical ratio of receding to static contact angles. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M4.00008: Buckling instability of a pinned droplet Gwynn Elfring, Eric Lauga Pinned droplets have been experimentally observed to develop a shape instability when squeezed against a non-wetting surface. Using a combination of analysis and simulation we show that this instability occurs regardless of the contact angle of the surface due to a geometric bifurcation past a critical conformation in a manner reminiscent of a liquid bridge between two columns. We characterize the transition of a droplet from symmetric to asymmetric conformations and show how this leads to a buckling of the bubble under a load. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M4.00009: Effects of particle number on interaction of particles with contact line in inkjet-printed evaporating colloidal drops Ying Sun, Viral Chhasatia The deposition behavior of inkjet-printed aqueous colloidal drops onto glass substrates with systematically varied wettability has been investigated by using fluorescence microscopy and a high-resolution goniometer. Real-time side-view images show that the contact angle of an evaporating colloidal drop is a function of the number of particles in suspension. The number of particles here is changed either by changing particle volume fraction while keeping particle size as a constant or by changing the particle size (10, 55, and 550 nm in radius) while keeping the particle volume fraction as a constant. During different stages of evaporation, the interplay of surface tension, drag due to evaporative flow, and particle-substrate interactions, rearranges particles inside a colloidal drop near the contact line region. These forces depend upon the size of the particles; however, the net effect of all these forces is independent of particle size. As the number of particles increase inside a drop, the receding contact angle of the evaporating drop decreases due to pinning of particles near the contact line. This reduction in receding contact angle increases the diameter of the particle deposition. The size of the particles affects the deposition diameter as smaller particles can move closer to the contact line compared to the larger particles and have a larger deposition diameter. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M4.00010: Contact line pinning of a perfectly wetting and volatile liquid at a sharp edge Yannis Tsoumpas, Sam Dehaeck, Alexey Rednikov, Pierre Colinet According to the Gibbs' criterion, a sharp edge can act as an energy barrier during the spreading of a liquid drop on a rigid substrate. In this study, however, we are trying to determine experimentally whether Gibbs' criterion is also valid for the case of a perfectly wetting and volatile liquid. To this purpose, we constructed a groove of triangular cross section on a Plexiglas substrate. During the experiments liquid was injected in the region surrounded by the groove, which had a square shape with rounded corners. The results indicated that a microgroove edge can indeed prevent the spreading of the liquid drop up to a certain extent, with the maximum apparent contact angle being in close agreement with the one given by Gibbs' criterion. Nevertheless, the apparent contact angle at breakup was found to be significantly lower in the corner of our region. To study this further we developed a static model, which takes into account surface tension and gravity but not the evaporation. Both the simulations and the experiments have confirmed a remarkable behaviour of the contact line at the corner. Finally, to grasp the effect of evaporation, experiments have also been conducted with drops of equally wetting but less volatile liquids. [Preview Abstract] |
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