Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J20: Focus Session: Microfluidics and Nanofluidics IV: Hydrodynamics, Separations and Slip |
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Sponsoring Units: DPOLY DFD GSNP Chair: Vivek Sharma, University of Illinois at Chicago Room: 405 |
Tuesday, March 4, 2014 2:30PM - 3:06PM |
J20.00001: DILLON MEDAL SYMPOSIUM BREAK |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J20.00002: Drainage and Stratification Kinetics of Foam Films Yiran Zhang, Vivek Sharma Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Foam lifetime, drainage kinetics and stability are strongly influenced by surfactant type (ionic vs non-ionic), and added proteins, particles or polymers modify typical responses. The rate at which fluid drains out from a foam film, i.e. drainage kinetics, is determined in the last stages primarily by molecular interactions and capillarity. Interestingly, for certain low molecular weight surfactants, colloids and polyelectrolyte-surfactant mixtures, a layered ordering of molecules, micelles or particles inside the foam films leads to a stepwise thinning phenomena called stratification. Though stratification is observed in many confined systems including foam films containing particles or polyelectrolytes, films containing globular proteins seem not to show this behavior. Using a Scheludko-type cell, we experimentally study the drainage and stratification kinetics of horizontal foam films formed by protein-surfactant mixtures, and carefully determine how the presence of proteins influences the hydrodynamics and thermodynamics of foam films. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J20.00003: Hydrodynamically enforced entropic trapping of Brownian particles Steffen Martens, Gerhard Schmid, Arthur Straube, Lutz Schimansky-Geier, Peter H\"anggi In small systems on length scales spatial confinement causes entropic forces that in turn implies spectacular consequences for the control for mass and charge transport. In view of its importance, recent efforts in theory triggered activities which allow for an approximate description that involves a reduction of dimensionality; thus making detailed predictions tractable. Up to present days, the focus was on the role of conservative forces and its interplay with confinement. Within the presented work, we overcome this limitation and succeeded in considering also non-conservative forces that derive from a vector potential [S. Martens et al., PRL 110, 010601 (2013)]. A relevant application is the fluid flow across microfluidic structures where a solute of Brownian particles is subject to both, an external bias and a pressure-driven flow. Then a new phenomenon emerges; namely, the intriguing finding of identically vanishing average particle flow which is accompanied by a colossal suppression of diffusion. This entropy-induced phenomenon, which we termed hydrodynamically enforced entropic trapping, offers the unique opportunity to separate particles of the same size in a tunable manner [S. Martens et al., Eur. Phys. ST 222, 2453-2463 (2013)]. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J20.00004: First clues to understand red blood cell interactions: numerical studies of vesicle suspensions Marine Thi\'ebaud, Chaouqi Misbah The scientific community started raising questions on blood flow for nearly two centuries, a period traced back to the pioneering work of Poiseuille. This topic has known a considerable upsurge of interest during the past decade. Vesicles capture several essential features shared with red blood cells. A single vesicle is now fairly understood, whereas study of suspensions is still unclear. We conduct bidimensionnal numerical studies by mean of the boundary integral method. Confinement plays a major role in that it introduces an interaction cut-off length. I will present results on the behavior of relative viscosity as function of the viscosity contrast between the fluid encapsulated by vesicles and the ambient fluid. This viscosity contrast is a key parameter: it triggers transition from tank-treading to tumbling regimes. Historical characterization of blood have led to the discovery of the Fahraeus-Lindqvist effect. I will introduce some results on this effect with a rheological study as function of concentration and confinement. I will report on non-standard behavior induced by a subtle spatio-temporal organization of the suspension. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 4:18PM |
J20.00005: Separation in microfluidics using periodic structures Invited Speaker: German Drazer We investigate the complex behavior that takes place during the motion of suspended particles in periodic systems, both when Brownian motion is important as well as when transport is nearly deterministic. We are interested in the development of separation devices that rely on the unique features of transport in periodic structures. A typical system in our studies consists of suspended particles moving either through a periodic array of posts or on top of a periodic pattern fabricated in the bottom surface of a microfluidic channel. In all cases, we investigate how to take advantage of the selective and repetitive effects present in periodic systems to promote and amplify the separation of a mixture of suspended particles. In particular, we focus on vector separation systems in which different species move in different directions within the device. We present analytical and experimental results that show the potential that periodic systems have to induce the spontaneous fractionation of a mixture of particles. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J20.00006: Slip effects in dewetting polymer microdroplets Joshua D. McGraw, Thomas Salez, Simon Maurer, Tak Shing Chan, Michael Benzaquen, Martin Brinkmann, \'{E}lie Rapha\"{e}l, Karin Jacobs Spherical caps on a substrate with less than equilibrium contact angles contract as a result of capillary forces. Applying the classical no-slip condition at the liquid-substrate interface results in diverging stress at the contact line. This divergence can be alleviated, however, by allowing finite flow velocity at the substrate, corresponding to the slip boundary condition. Experiments have been conducted in which glassy polystyrene microdroplets are placed upon, as substrates, different self-assembled monolayers (SAMs). The spherical caps are prepared such that initial contact angles are much less than the equilibrium contact angle. Above the glass transition temperature, a capillary induced flow is observed; the droplet radii shrink while their heights grow. Furthermore, the intermediate height profiles are highly non-spherical. Different SAMs give rise to differing slip lengths, resulting in dramatic changes to the temporal and morphological path these tiny droplets take toward their equilibrium spherical cap shapes. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J20.00007: Imbibition dynamics on surfaces of legs of a small animal and on artificial surfaces mimicking them Marie Tani, Daisuke Ishii, Shuto Ito, Takahiko Hariyama, Masatsugu Shimomura, Ko Okumura Recently, imbibition of textured surfaces covered with homogeneous micro-pillar arrays has been actively studied partly because of the potential for transport of a small amount of liquids. In most cases, the dynamics is described by the Washburn law, in which the imbibition distance scales with the square root of elapsed time, while a different scaling law has been recently found [1]. In this study, we studied imbibition on legs of a small animal that absorbs water via its legs [2] to find yet another scaling law. Furthermore, imbibition of artificial surfaces mimicking the leg surface was found to be described well by a composite theory.\\[4pt] [1] Obara and Okumura, Phys. Rev. E 86, 020601R (2012).\\[0pt] [2] Ishii, Horiguchi et al. Sci. Rep. 3, 3024 (2013). [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J20.00008: Wall Driven Cavity Approach to Slug Flow Modeling In a Micro channel Avinash Sahu, Shekhar Kulkarni, Subramaniam Pushpavanam Slug flow is a commonly observed stable regime and occurs at relatively low flow rates of the fluids. Wettability of channel decides continuous and discrete phases. In these types of biphasic flows, the fluid -- fluid interface acts as a barrier that prohibits species movement across the interface. The flow inside a slug is qualitatively similar to the well known shallow cavity flow. In shallow cavities the flow mimics the ``fully developed'' internal circulation in slug flows. Another approach to slug flow modeling can be in a moving reference frame. Here the wall boundary moves in the direction opposite to that of the flow, hence induces circulations within the phases which is analogous to the well known Lid Driven Cavity. The two parallel walls are moved in the opposite directions which generate circulation patterns, equivalent to the ones regularly observed in slug flow in micro channels. A fourth order stream function equation is solved using finite difference approach. The flow field obtained using the two approaches will be used to analyze the effect on mass transfer and chemical reactions in the micro channel. The internal circulations and the performance of these systems will be validated experimentally. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J20.00009: Some scaling laws for fluid dynamics in a confined space Ko Okumura This talk is composed of several topics of fluid dynamics in confined spaces. Scaling laws and simple physical understanding is stressed in this talk. Wetting on textured surfaces where array of pillars of micron scale are arranged is one of the topics, which include wetting transition of a drop on the surfaces and capillary rise on textured surfaces at the micron scale. For the capillary rise, we discuss a new type of scaling law resulting from competition of three effects: capillary drive, viscous and gravitational drags [1]. We also discuss drag frictions acting on fluids in confined spaces, in which liquid film is confined on the micron scale and the role of the film is important for understanding the physics of the drag [2]. Other topics include the coalescence of liquid drops in a confined space in different situations. Especially, we discuss the effect of high electric field in the coalescence phenomena on the system studied in [3]. In addition, formation of liquid thin film and bursting of the film during liquid-drop coalescence are also discussed.\\[4pt] [1] Noriko OBARA and K.O., Phys. Rev. E 86, 020601R (2012).\\[0pt] [2] Ayako ERI and K.O., Soft Matter, 7, 5648 (2011).\\[0pt] [3] Maria YOKOTA and K.O., Proc. Nat. Acad. Sci. (USA), 108 (2011) 6395. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J20.00010: First-Principles Investigation on Water dynamics at Functionalized Silicon surface Donghwa Lee, Eric Schwegler, Yosuke Kanai Interfacial water behavior at semiconductor surfaces is one of the most important areas of investigation for diverse industrial applications such as crystal growth, lubrication, catalysis, electrochemistry and sensors. Although the hydrophobicity at surface is widely recognized to be important in determining the behavior of water molecules near the surface, we show that subtle molecular details may also play a role in determining the dynamical behavior of water by employing first principles molecular dynamics simulations. By comparing water diffusivity at three non-polar surfaces, we find that water diffusivity is significantly faster near the H-terminated surface as compared to either CH3- or CF3-terminated surfaces. By examining the interfaces in detail, we find that the specific surface corrugation that is characteristic of the H-terminated surface leads to a suppression of hydrogen bond network ring structures by enhancing hexagonal spatial distribution of water molecules near the surface. Such a distinct molecular dependent behavior of the interfacial water was found to persist well into the liquid, while the most structural properties are noticeably influenced in only the first water layer ($\sim$5 {\AA}). [Preview Abstract] |
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