Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session D27: Surface Tension: Experimental Methods and Measurements |
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Chair: Hyoungsoo Kim, Princeton University Room: E147-148 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D27.00001: Alcohol drops on miscible liquid: mixing or spreading? Hyoungsoo Kim, Koen Muller, Orest Shardt, Shahriar Afkhami, Howard Stone $-abstract-$We studied how a sessile drop of alcohol behaves when placed on a fully miscible liquid. The dynamics of the subsequent mixing and spreading were captured by using a high-speed camera and investigated by varying parameters (e.g., surface tension, density, and viscosity). We observed that a deposited alcohol drop on a liquid bath remains as a floating lens shape, the alcohol liquid leaks out along the rim of the droplet, and it spreads axi-symmetrically along the bottom liquid interface. To visualize spreading and mixing features, we used time-resolved Particle Tacking Velocimetry and a Schlieren method. We observed a localized mixing flow at the rim of the floating droplet where the maximum flow speed is obtained, driven by a solutal Marangoni effect. Underneath the interface of the bath liquid, a viscous boundary layer develops while the alcohol liquid spreads along the radial direction. We also observed a finite quasi-steady interfacial flow velocity regime after the alcohol droplet touched the bottom liquid surface. In this regime, the flow speed linearly increases inside the floating lens, and outside the lens the flow speed decays along the r-direction with a power-law slope, $U_{r} \sim r^{-1/2}$. Physical arguments to support the observations will be discussed. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D27.00002: Elasto-capillary torsion at a liquid interface Alexandros Oratis, Timothy Farmer, James Bird When a liquid drop wets a solid, the droplet typically spreads over the solid. By contrast, for sufficiently compliant solids, the solid can instead spread around the drop. This wrapping phenomenon has been exploited to assemble 3-dimensional structures from 2-dimensional sheets, a process often referred to as capillary origami. Although existing studies of this self-assembly have demonstrated bending and folding, methods of inducing spontaneous twisting by means of capillarity are less clear. Here we demonstrate that spontaneous twist can be initiated in a compliant solid through a combination of surface chemistry and capillarity. Experimentally, we measure the angle of twist on a surface with binary patterns of surface wettability as we vary the solid's geometric and material properties. We develop a scaling law to relate this angle of twist to the elastic and interfacial properties, which compares well with our experimental results. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D27.00003: A Comparative Study of the Effect of Surfactant and Temperature in Fluid Interfaces. Aldo H. Cortes-Estrada, Laura A. Ibarra-Bracamontes, Alicia Aguilar-Corona, Gonzalo Viramontes-Gamboa A fluid interface is the boundary region formed when two immiscible fluids come into contact. One of the most important properties of fluid interfaces is the interfacial tension. The interfacial tension between two fluids can be modified by the presence of surfactant. In addition, the temperature is a relevant factor that can also modify the interfacial properties. In this work the behavior of the interface formed by oil and water in the presence of surfactant at different temperatures is presented. Interfacial tension measurements were obtained by the Pendant Drop technique. Two types of surfactant were tested, Sodium Dodecyl Sulfate (SDS) as a hydrophilic surfactant, and Sorbitan Monooleate (Span 80) as a lipophilic surfactant. The range of variations in temperature was from 25 to 60 Celsius degree. Hexane or Dodecane was used as the oil phase. The main results showed that the lipophilic surfactant showed a greater efficiency with respect to the hydrophilic surfactant used. As the temperature increased in the range considered an exponential decay for the interfacial tension was observed. This decay was dominated by the surfactant concentration. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D27.00004: The spontaneous puncture of thick liquid films Baptiste Néel, Emmanuel Villermaux We call thick those films for which the disjoining pressure is ineffective. Water films with thickness $h$ in the 1-10 $\mu$m range are thick, but it is also known that, paradoxically, they nucleate holes spontaneously. We have uncovered a mechanism solving the paradox. Most natural films are dirty to some extent, and we show that if a spot of dissolved substance lowers locally the surface tension of the liquid, the corresponding Marangoni stress may lead to a self-sustained instability triggering film rupture. When deposited with size $a$, the spot dissipates by molecular diffusion (coefficient $D$) along the film in a time $a^2/D$. Before doing so, the surface tension gradient $\Delta\sigma/a$ between the spot center (tension $\sigma-\Delta\sigma$) and the rest of the film (tension $\sigma$) induces an inhomogeneous outward interstitial flow which digs the spot, and reinforces the tension gradient. Hence the instability, which occurs within a timescale $\tau\sim\sqrt{\rho a^2 h/\Delta \sigma}$, with $\rho$ the liquid density. When the Péclet number $Pe=a^2/D\tau$ is small, diffusion regularizes the film, which remains flat: clean films don’t break, while for $Pe>1$, the film punctures. This new scenario will be illustrated by several experiments. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D27.00005: Evaporation of water between two microspheres: how wetting affects drying. Kun Cho, Yeseul Kim, Jun Lim, Joon Heon Kim, Byung Mook Weon When a small volume of water is confined between microparticles or nanoparticles, its evaporation behavior can be influenced by wettability of particles. This situation frequently appears in coating or printing of colloidal drops in which colloidal particles are uniformly dispersed into a liquid. To explore water evaporation between particles, here we study on evaporation dynamics of water between two microspheres by utilizing high-resolution X-ray microscopy for side views and optical microscopy for bottom views. We find that evaporating water gets pinned on microsphere surfaces, due to a force balance among air, water, and microspheres. Side and bottom views of evaporating water enable us to evaluate water curvature evolution around microspheres before and after pinning. Interestingly curvature evolution is controlled by cooperation of evaporation and wetting dynamics. This study would be useful in identifying and controlling of coating or printing for colloidal drops. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D27.00006: Elasticity of Flowing Soap films Ildoo Kim, Shreyas Mandre The robustness of soap films and bubbles manifests their mechanical stability. The single most important factor underlying the mechanical stability of soap films is its elasticity. Non-destructive measurement of the elasticity in these films has been cumbersome, because of its flowing nature. Here we provide a convenient, reproducible, and non-destructive method for measuring the elasticity by generating and inspecting Marangoni waves. Our method is based on generating an oblique shock by inserting a thin cylindrical obstacle in the flowing film, and converting the measured the shock angle to elasticity. Using this method, we find a constant value for the elasticity of 22 dyne/cm in the commonly used range of film widths, thicknesses or flow rates, implying that the surface of the film is chemically saturated with soap molecules. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D27.00007: Large-scale fluid circulation induced by asymmetric surface under vertical vibration Yi-Cheng Huang, Jun Zhang, Jin-Qiang Zhong A thick layer of fluid, water, contained in a rectangular box of a few centimeters in each direction, is deformed asymmetrically on its free surface by the imposed boundary wettability. As the fluid layer is subject to harmonic excitation at a level below the threshold of Faraday instability, an unidirectional, large-scale circulation emerges in the fluid bulk. We experimentally study its pattern, timescale needed to evolve and the underlying mechanisms. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D27.00008: Capillary deposition of advected floating particles Emilie Dressaire, Aymeric Debaisieux, Federico Gregori The deposition and aggregation of particles flowing through a confined environment can dramatically hinder the transport of suspensions. Yet, the mechanisms responsible for the deposition of particles in shear flow are not fully understood. Here, we use an experimental model system in which floating particles are advected on the surface of a water channel and deposited on fixed obstacles through attractive capillary effects. By varying the flow rate of the liquid, the wetting properties and size of the particles and obstacles, we can tune the magnitude of the capillary and hydrodynamic forces that determine the probability of deposition and the equilibrium position on the substrate. We show that arrays of obstacles can be designed to efficiently capture the floating particles advected by the flow. [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D27.00009: Writing on water with permanent markers sepideh khodaparast, Fran\c{c}ois Boulogne, Howard A. Stone Permanent markers create a continuous thin stain on a surface, which, after drying, can only be removed by high pressure cleaning or organic solvents. The stains of the markers are hydrophobic and thus effectively resist rinsing by water. We introduce a peeling technique based on surface tension, which benefits from this hydrophobicity, to transfer complex two-dimensional marks onto the air-water interface. As an air-water meniscus reaches the stain edge, the surface tension applies a detachment force to the thin layer. If larger than the adhesion of the stain on the substrate, the surface tension can peel off the entire layer. We examine the efficiency of this peeling method for elastic thin films in an experimental model made of thin polystyrene films of well-controlled geometrical properties adhering on clean glass substrates. We investigate the effect of film thickness and interface velocity. At low interface velocities $U<1$ mm/s, films of thicknesses down to 50 nm are peeled and transferred to the air-water interface with no defects. Peeling with the meniscus can be used in a large variety of applications such as water-assisted transfer printing, peel-and-stick technologies, cleaning the water proof stains without solvent and fabrication of flexible wearable electronics. [Preview Abstract] |
Sunday, November 20, 2016 4:54PM - 5:07PM |
D27.00010: Dynamics of surface tension driven mixing of an alcohol droplet with water. Raj Dandekar, Anurag Pant, Baburaj Puthenveettil We study the flow induced by the surface tension driven spreading of an ethanol droplet of radius r$_{\mathrm{d}}$ on the surface of a 5mm water layer, visualizing the flow using aluminium flakes on the surface of the water layer with backlighting and high speed imaging. The concentration of tracer aluminium particles was found to have no effect on the scaling law for spreading.The drop,when brought in contact with the water surface causes a local depression in surface tension ,resulting in a thin circular region to expand radially outwards.We observe that the dimensionless radius of the expanding front (r*$=$r/r$_{\mathrm{d}})$ scales with the dimensionless time (t*$=\mu $ r$_{\mathrm{d\thinspace }}$/$\Delta \gamma )$, as r*$\sim $t*$^{\mathrm{1/4}}$,where $\mu $ is the viscosity of water and $\Delta \gamma $ is the surface tension difference between water and the ethanol droplet.A scaling analysis taking the viscous and the marangoni forces into account explains the observed scaling law.Our observations differ from that in the case of continuous alcohol supply (S\'{a}nchez et al.,Phys.Fluids 27, 032003, 2015) where the observed scaling law is r*$\sim $t*$^{\mathrm{1/2}}$.The expanding front radius reaches a maximum value and then decreases with time. [Preview Abstract] |
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