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 H10: Microscale Flows: Interfaces and Wetting |
Hide Abstracts |
Chair: Xin Yong, Binghamton University Room: 3005 |
Monday, November 24, 2014 10:30AM - 10:43AM |
H10.00001: Reentry to the two-thirds power law for the surfactant-laden Bretherton problem in a slippery tube David Halpern, Hsien-Hung Wei Recent reports on the clean-interface Bretherton problem show that the well-known two-thirds power law can break down due to wall slip (Liao et al. Phys. Rev. Lett. 111, 136001, 2013; Li et al. J. Fluid Mech. 741, 200-227, 2014). Instead, the film thickness can vary quadratically with the capillary number Ca for Ca below some critical value, corresponding to the situation where slip effects are strong. Here we find that the presence of insoluble surfactant completely changes the above result. Specifically, combined effects of surfactant and wall slip can not only make the strong-slip quadratic law disappear, but also completely suppress the usual Marangoni film thickening along the two-thirds law, making the film behave as if surfactant and wall slip were absent. How to test the above finding experimentally is also discussed. [Preview Abstract] |
Monday, November 24, 2014 10:43AM - 10:56AM |
H10.00002: Coupling Molecular Dynamics to Continuum Computational Fluid Dynamics to simulate Superspreading at the macro-scale Edward Smith, Panagiotis Theodorakis, Erich Muller, Richard Craster, Omar Matar Superspreading surfactants are widely researched, due to their fascinating properties and their many potential applications. However, the mechanism behind superspreading is still poorly understood. Karapetsas et al. (JFM, 2011) demonstrated that surfactant absorption at the contact line is of critical importance by a simple constitutive law in a continuum solver. Molecular dynamics (MD) has the ability to elucidate the details of this mechanism, replacing the constitutive law with explicit modelling of the surfactant, fluid and solid interactions at the contact line. However, MD is computationally-expensive and usually limited to nano-scale problems. We couple both continuum and molecular models in a single simulation so that the mechanism at the contact-line can be explicitly simulated at the molecular scale, while the continuum model can be employed throughout the remaining domain. This allows simulations on scales which approach macroscale experiments while maintaining the vital molecular details. Here, the required coupling techniques to implement the proposed solution are discussed: obtaining continuum boundary conditions by averaging molecules, applying constraint force to the molecular region, addition or removal of molecules and software for coupled simulation on HPC. [Preview Abstract] |
Monday, November 24, 2014 10:56AM - 11:09AM |
H10.00003: Characteristic Structure of Forced Wetting Mengfei He, Sidney Nagel As a solid plate is lowered vertically into a tank of liquid, the plate will entrain some of the surrounding air. The contact line between the gas, liquid, and solid will be pushed below the original surface height of the liquid. When the dipping velocity surpasses a critical speed, a transition takes place. At that point the contact becomes elongated and, in the final steady state, form a V-shaped cavity of air surrounded on one side by the solid plate and the other side by the liquid [1]. Using interference imaging, we find that there is a characteristic structure to the thickness of the entrained air layer. Not only is there a thick region of air at the edge of the cavity, but there is also characteristic V-shaped regions at the two top corners. The thick region around the edge is reminiscent of the ridge structures observed in dewetting [2]. The non-uniformity of the air pocket geometry suggests a non-uniformity of the air flow distribution, which further suggests a new instability related to the air pocket dynamics. \\[4pt] [1] T D Blake and K J Ruschak, Nature (London) 282, 489(1979)\\[0pt] [2] J H Snoeijer, G Delon, M Fermigier and B Andreotti, PRL 96, 174504(2006) [Preview Abstract] |
Monday, November 24, 2014 11:09AM - 11:22AM |
H10.00004: Dynamics of a capillary invasion in a closed-end capillary Hosub Lim, Anubhav Tripathi, Jinkee Lee The position of fluid invasion in an open capillary increases as the square root of time and ceases when the capillary and hydrostatic forces are balanced, when viscous and inertia terms are negligible. Although this fluid invasion into open-end capillaries has been well described, detailed studies of fluid invasion in closed-end capillaries have not been explored thoroughly. Thus, we demonstrated, both theoretically and experimentally, a fluid invasion in closed-end capillaries, where the movement of the meniscus and the invasion velocity are accompanied by adiabatic gas compression inside the capillary. Theoretically, we found the fluid oscillations during invasion at short time scales by solving the one dimensional momentum balance. This oscillatory motion is evaluated in order to determine which physical forces dominate the different conditions, and is further described by a damped driven harmonic oscillator model. However, this oscillating motion is not observed in the experiments. This inconsistency is due to the following; first, a continuous decrease in the radius of the curvature caused by decreasing the invasion velocity and increasing pressure inside the close-ended capillary, and second, the shear stress increase in the short time scale by the plug like velocity profile within the entrance length. The viscous term of modified momentum equation can be written as $K\frac{8\mu \ell }{r_{c}^{2} }\frac{d\ell }{dt}$ by using the multiplying factor $K$, which represents the increase of shear stress. The $K$ is 7.3, 5.1 and 4.8 while capillary aspect ratio $\chi_c$ is 740, 1008 and 1244, respectively. [Preview Abstract] |
Monday, November 24, 2014 11:22AM - 11:35AM |
H10.00005: Overflow cascades on liquid-infused surfaces Ian Jacobi, Jason Wexler, Howard Stone The shear-driven dewetting of liquid-infused, micro-patterned surfaces is shown to exhibit a complex cascade of overflow, droplet generation and liquid displacement behaviors. Because liquid-infused surfaces are important in systems as varied as free-surface microfluidic devices and high Reynolds number drag-reducing coatings, understanding the dewetting mechanism is crucial to designing substrates capable of retaining infused liquid or, alternatively, dispensing it in a controlled way. Shear flow experiments on a variety of liquid-infused surface architectures are performed and the interfacial dynamics are characterized at macro- and microscopic scales. Analysis of the different stages of the dewetting cascade is then used to develop substrate design criteria for enhanced liquid control under a variety of shear flow conditions. [Preview Abstract] |
Monday, November 24, 2014 11:35AM - 11:48AM |
H10.00006: Acoustic spreading of thin films of water: balancing capillary, viscous, and vibrational mechanisms Ofer Manor, Gennady Altshuler Substrate vibrations at frequencies comparable to HF radio frequencies and in contact with liquid generate flow at submicron length scales that may result in spreading of liquid films. This spreading mechanism is thought as a way of manipulating liquids on microfluidic platforms. In previous studies we used silicon oil as a model liquid; silicon oil spread easily and smoothly as long as the oil and substrate vibrations are in contact. Water films under similar conditions, however, were observed to spread to a minute extent and only under high power levels that further render intense capillary instabilities. In this presentation we use theory and experimental evidence to discuss the physical mechanisms associated with acoustic spreading of water films. We highlight mechanisms associated with acoustic spreading of arbitrary liquids, and we show the various influences of these mechanisms on liquid spreading is encapsulated within one dimensionless number whose value determines whether spreading is to take place. We further elucidate the discrepancy, observed in earlier literature, between the response of oil and water to acoustic excitation and highlight an intermediate parametric region, where precise manipulation of water spreading is achieved by carefully balancing the governing mechanisms. [Preview Abstract] |
Monday, November 24, 2014 11:48AM - 12:01PM |
H10.00007: Drag reduction on liquid infused superhydrophobic surfaces Jeong-Hyun Kim, Jonathan Rothstein The drag reduction on liquid infused superhydrophobic surfaces was measured through a microchannel. The microfluidic device consisted of two halves, a superhydrophobic surface and a microchannel, respectively. The superhydrophobic surface was created from a silicon wafer with ridge patterns 30 to 60 microns in width and spacing generated by a standard photolithography. A low viscosity, immiscible, incompressible silicone oil was filled to the gaps of the superhydrophobic surfaces. Several microchannels varying in size from 100 to 200 microns were fabricated from PDMS with an inlet, outlet and two pressure ports. After flow coating the superhydrophobic surface with a uniform film of oil, the two halves were aligned and clamped together and the pressure drop measured. A systematic study on drag reduction and slip length was performed by varying the viscosity ratio between the water and oil phase between 0 to 50. Several aqueous glycerin solutions with different viscosity were prepared. The slip length, pressure drop, and longevity of the oil phase were studied as a function of surface geometry, capillary number and the dispense volume. [Preview Abstract] |
Monday, November 24, 2014 12:01PM - 12:14PM |
H10.00008: A Microfluidic Platform for Interfacial Electrophoretic Deposition Young Soo Joung, Jeffrey Moran, Andrew Jones, Eric Bailey, Cullen Buie Composite membranes of hydrogel and carbon nanotubes (CNTs) are fabricated using electrophoretic deposition (EPD) at the interface of two immiscible liquids in microfluidic channels. Microfluidic channels, which have two parallel electrodes at the walls, are used to create electric fields across the interface of oil and water continuously supplied into the channels. Depending on the Reynolds (Re) and Weber (We) numbers of oil and water, we observe different formations of the interface. Once we find the optimal Re and We to create a planar interface in the channel, we apply an electric field across the interface for EPD of CNTs and/or silver (Ag) nanorods dispersed in water. During EPD, particles migrate to the oil/water interface, where cross-linking of polymers is induced to form composite hydrogel membranes. Properties of the composite hydrogel films are controlled by electric fields, CNT concentrations, and both Re and We numbers, allowing for continuous production. This fabrication method is effective to create composite polymer membranes placed in microfluidic devices with tunable electrical, mechanical, and biological properties. Potential applications include fabrication of doped hydrogels for drug delivery, conductive hydrogels for biological sensing, and electron permeable membranes for water splitting and osmotic power generation. [Preview Abstract] |
Monday, November 24, 2014 12:14PM - 12:27PM |
H10.00009: Influence of spatial variation of phenomenological parameters on the modeling of boundary conditions for flows with dynamic wetting Yuka Hizumi, Takeshi Omori, Yasutaka Yamaguchi, Takeo Kajisima For reliable prediction of multiphase flows in micro- and nano-scales, continuum models are expected to account for small scale physics near the contact line (CL) region. Some existing works (for example the series of papers by the group of Qian and Ren) have been successful in deriving continuum models and corresponding boundary conditions which reproduce well the molecular dynamics (MD) simulation results. Their studies, however, did not fully address the issue of adsorption layer especially in the CL region, and it is still not clear if general conclusion can be deduced from their results. In the present study we investigate in detail the local viscosity and the corresponding stress tensor formulation in the solid-liquid interface and in the CL region of immiscible two-phase Couette flows by means of MD simulation. The application limit of the generalized Navier boundary condition and the continuum model with uniform viscosity is addressed by systematic coarse-graining of sampling bins. [Preview Abstract] |
Monday, November 24, 2014 12:27PM - 12:40PM |
H10.00010: Molecular-like hierarchical self-assembly of monolayers of mixtures of particles P. Singh, M. Hossian, S. Gurupatham, K. Shah, A. Amah, M. Janjua, S. Nudurupati, I. Fischer, N. Aubry We present a technique that uses an externally applied electric field to self-assemble monolayers of mixtures of particles into molecular-like hierarchical arrangements on fluid-liquid interfaces. The arrangements consist of composite particles (analogous to molecules) which are arranged in a pattern. The structure of a composite particle depends on factors such as the relative sizes of the particles and their polarizabilities, and the electric field intensity. If the particles sizes differ by a factor of two or more, the composite particle has a larger particle at its core and several smaller particles forming a ring around it. The number of particles in the ring and the spacing between the composite particles depends on their polarizabilities and the electric field intensity. Approximately same sized particles form chains (analogous to polymeric molecules) in which positively and negatively polarized particles alternate. [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