Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session LS: Drops X |
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Chair: Osman Basaran, Purdue University Room: Long Beach Convention Center Grand Ballroom A |
Monday, November 22, 2010 3:35PM - 3:48PM |
LS.00001: Effect of contact line dynamics on capillary wave scattering by an infinitesimal barrier Likun Zhang, David Thiessen Novel fluid configurations are possible at zero Bond number when capillary instabilities are countered by minimal solid support structures such as thin wires. Large aspect ratio liquid cylinders can be stabilized by an array of solid rings or by a helix. Capillary wave propagation on such channels involves scattering by a periodic array of barriers. The transmission and reflection of capillary waves by a single infinitesimal transverse barrier is considered theoretically by a matched evanescent wave expansion. An effective-slip boundary condition is applied for which the contact-line velocity is proportional to the deviation of the contact angle from its equilibrium value. Energy dissipation at the barrier is found to be most effective when the phase velocity is close to the phenomenological slip coefficient. The scattering of capillary waves on a liquid cylinder by a transverse ring agrees in the short-wave limit with the theory of gravity- capillary wave scattering by a transverse surface-piercing barrier in the limit of zero Bond number and zero barrier depth. [Preview Abstract] |
Monday, November 22, 2010 3:48PM - 4:01PM |
LS.00002: Contact-line pinning of a perfectly wetting volatile liquid overfilling a square hole with a tiny triangular groove along its perimeter: experiments and theoretical static shapes Yannis Tsoumpas, Sam Dehaeck, Alexey Rednikov, Pierre Colinet Contact lines will stay pinned at sharp edges until they exceed a certain equilibrium angle as the Gibbs's criterion indicates. In this preliminary study, we are trying to determine whether a groove can prevent a perfectly wetting liquid from spreading out of a square hole on the substrate. To this purpose, a highly-volatile electronic liquid has been chosen while the substrate was made of a polycarbonate plate with a square hole closely surrounded by a tiny groove of triangular cross- section. The results have shown this to act as an effective barrier, and the apparent contact angle (with respect to the horizontal) can attain considerable values. Moreover, the experiments indicated that the liquid drop adopts a shape with the apparent contact angle at the corners being much smaller than at other locations along the edge. This is explained on the basis of a simple static model including surface tension and gravity. The role of evaporation is also assessed. [Preview Abstract] |
Monday, November 22, 2010 4:01PM - 4:14PM |
LS.00003: A simple feedback algorithm to predict the contact angle with contact angle hysteresis Jun Kwon Park, Kwan Hyoung Kang In numerical analysis of contact-line problems, contact angle model plays an important role in predicting the motion of contact line. We developed a simple feedback algorithm to numerically predict the contact angle with considering the contact angle hysteresis. This algorithm automatically find equilibrium contact angle which is between advancing and receding contact angle and the pinning position of contact line. We applied the numerical method to analyze the impacting droplet on a dry surface incorporating contact angle hysteresis and dynamic contact angle model. The numerical results showed good agreement with experimental data for the overall dynamics of the droplet, and the pinning process of contact line was also predicted well. [Preview Abstract] |
Monday, November 22, 2010 4:14PM - 4:27PM |
LS.00004: Contact angle hysteresis at the nanometer scale Thierry Ondarcuhu, Mathieu Delmas, Marc Monthioux Whereas thermodynamics predicts that the contact angle of a liquid droplet at rest on a solid surface is given by the Young-Dupr\'{e} equation, experiments on real solid surfaces show that this contact angle is not univocal but exhibits a hysteresis which depends on the droplet history. Despite many theoretical and experimental studies devoted to this problem, a quantitative correlation between contact angle hysteresis and surface defects shape or repartition is still lacking. Here, we study the pinning of a contact line on nanometric defects by measuring, by atomic force microscopy, the capillary force exerted by a liquid on a carbon tip. This original quasi-1D geometry allowed us to study nanometric defects. We observe localized jumps which results from the pinning of the contact line on individual defects. A detailed study of the force curves validates the theory of weak and strong defects, postulated by Joanny {\&} de Gennes (J. Chem. Phys., 81 (1984) 552). In particular, we bring the first experimental evidence of weak defects which do not contribute to hysteresis and study the energy dissipated on strong defects down to values of the order of kT. We then show how individual defects interact to give rise to contact angle hysteresis as measured at macroscopic scale, thus providing a precise description of the origin of contact angle hysteresis at nanometer scale. [Preview Abstract] |
Monday, November 22, 2010 4:27PM - 4:40PM |
LS.00005: Optical characteristics and nonlinear dynamics of a pinned-contact double droplet system Joseph Olles, Amir Hirsa, Michael Vogel Through the use of an oscillating double droplet system (DDS), an adaptive varifocal fluidic lens is created. Pinning the gas/liquid contact lines of the DDS eliminates viscous losses from moving contact lines and aids in simplifying the geometric parameter space. The use of millimeter scale diameters allows capillary effects to form stable droplets with spherical interfaces. We present a range of dependent parameters for the DDS as a fluidic lens which is made to oscillate by a sinusoidal pressure in millisecond cycles and various amplitudes. The lens is characterized through the following optical parameters throughout a cycle: sphericity, radius of curvature, focal length, and field stop. A non-linearity in the DDS's resonant frequency is identified at various volumes; slight changes in the amplitude of the driving pressure produces a substantial shift in the resonant frequency of the system. [Preview Abstract] |
Monday, November 22, 2010 4:40PM - 4:53PM |
LS.00006: Theoretical investigation of the motion of two-dimensional droplets on inclined substrates Nikos Savva, Serafim Kalliadasis We examine theoretically the dynamics of the motion of two- dimensional droplets on inclined topographical substrates. We take into account the effects of gravity and possible substrate vibrations. Assuming the pressence of slip on the substrate and that the contact angle there always remains equal to its static value, the long-wave limit of the Stokes' regime leads to a single equation for the evolution of the droplet thickness. Through a singular perturbation procedure, the flow in the vicinity of the contact points is asymptotically matched to the flow in the bulk of the droplet, to yield a set of integrodifferential equations for the location of the two droplet fronts. Our matching procedure is favorably compared with numerical solutions to the full problem. In the absence of vibrations, we find a substrate-induced hysteresis effect connected with the existence of a critical inclination angle beyond which the droplet can no longer be supported at equilibrium by the substrate. When substrate vibrations are present, we deduce criteria for the peculiar vibration-induced climbing of droplets reported in recent experiments. [Preview Abstract] |
Monday, November 22, 2010 4:53PM - 5:06PM |
LS.00007: Capillary-Based Liquid Micro/Nano Droplet Deposition Iskander Akhatov, Artur Lutfurakhmanov, Gregory Loken, Douglas Schulz Liquid droplet deposition through a capillary onto a substrate is studied. The application of pressure into the capillary causes a liquid meniscus to form at the outlet. Touching the substrate with the liquid meniscus and subsequent capillary retraction gives liquid deposition on the substrate. Theoretical and experimental studies of the steady liquid bridge structure between the capillary and substrate identified the range of parameters when deposition of small droplets (no blot) can be performed. Experiments revealed that in this range of parameters the size of deposited liquid droplets is less than 10-15{\%} of inner diameter of the capillary. A logical next step in the demonstration of this approach is to translate from the microscale to the nanoscale using a nanocapillary navigated by a scanning tunneling microscope. [Preview Abstract] |
Monday, November 22, 2010 5:06PM - 5:19PM |
LS.00008: Rapid wetting dynamics Andreas Carlson, Gabriele Bellani, Gustav Amberg Contact lines between solids and liquid or gas interfaces appear in very many instances of fluid flows. This could be coffee stains, water-oil mixtures in oil recovery, hydrophobic feet of insects or leaves in nature. In the present work we elucidate some of the wetting physics governing the very rapid wetting. Experimental and numerical results of spontaneously spreading droplets are presented, where focus is directed towards understanding the very rapid flow regime and highly dynamic initial wetting phase, where the contact line speed is limited by dissipative processes on a molecular scale occurring at the contact line. In particular we show the influence of the surface wettability and the liquid viscosity on the spreading dynamics, such as the contact line motion and dynamic contact angle in time. [Preview Abstract] |
Monday, November 22, 2010 5:19PM - 5:32PM |
LS.00009: Investigation of Contact Angle Behavior and Tilting Stability of Drops on Rough Surfaces Jason Schmucker, Edward White, Joshua Osterhout A method for measuring full-field, instantaneous drop interface profiles on rough surfaces has been implemented to study contact angles on metallic surfaces with micron-scale roughness. Water drops measured span a range of Bond numbers from $Bo = 0.5$ to $5$ on roughness in the range of $R_A=0.8$ to $4.9$. Experiments were conducted to provide data on contact angle variations about a single drop's contact line and to investigate how contact angle depends on surface roughness. The method has also been used to study the stability of drops to sliding on tilted surfaces. Modifications of the contact line and distributions of contact angle are observed as surface angle is increased to the point of incipient sliding. The sensitivity of the stability parameters to the initial configuration of the drop is detailed, particularly in reference to initial contact line shape. Results such as critical inclinations and contact angles are discussed and compared with previous studies in the literature, beginning with Bikerman [J.Coll.Sci. 5:4, 1950] and including ElSherbini and Jacobi [J.Coll.Sci. 273, 2004]. [Preview Abstract] |
Monday, November 22, 2010 5:32PM - 5:45PM |
LS.00010: ABSTRACT WITHDRAWN |
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