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 D37: Drops: Capillary Fluidics |
Hide Abstracts |
Chair: Serafim Kalliadasis, Imperial College - London Room: Portland Ballroom 252 |
Sunday, November 20, 2016 2:57PM - 3:10PM |
D37.00001: Self-organization of levitating droplets over a dry heated substrate Vladimir Ajaev, Dmitry Zaitsev, Dmitry Kirichenko, Oleg Kabov Levitating droplets of liquid condensate are known to organize themselves into ordered structures over hot liquid-gas interfaces. We report experimental observation of similar behavior over a dry heated surface. Even though the life-time of the structure is shorter in this case, its geometric characteristics are remarkably similar to the case of droplets levitating over liquid-gas interfaces. A simple model is developed that predicts the mechanisms of both droplet levitation and inter-droplet interaction leading to pattern formation over dry surface; the model is shown to be in excellent agreement with the experimental data. Using the insights from the new experiments, we are able to resolve some long-standing controversies pertaining to the mechanism of levitation of droplets over liquid-gas interfaces. [Preview Abstract] |
Sunday, November 20, 2016 3:10PM - 3:23PM |
D37.00002: Analysis of pumpless liquid transport on a wettability-patterned track Aritra Ghosh, Ken Brenner, Souvick Chatterjee, Pallab Sinha Mahapatra, Ranjan Ganguly, Constantine Megaridis Pumpless liquid transport can be achieved by tuning curvature of liquid volumes (Laplace pressure) on a diverging superhydrophilic track surrounded by a superhydrophobic background. The liquid, which starts in the form of a deposited droplet, propagates on the track as a well-defined bulge (bulk liquid) followed by a trailing liquid film conforming to the track geometry. In this work, we present a semi-analytical model to explain the trends of observed phenomena as well as the liquid transport dynamics (velocity, acceleration, flow rate) with respect to track geometry, solid wettability contrast, and feed volume. High speed image analysis of the motion of the bulk liquid is performed using a droplet shape tracking algorithm; dominant forces are identified and model predictions are compared with the experimental data. The combination of experimental and analytical tools offers new insight on a problem that is relevant to open-surface microfluidic devices, especially in the point of care (i.e. low cost) technological domain. [Preview Abstract] |
Sunday, November 20, 2016 3:23PM - 3:36PM |
D37.00003: Liquid spreading along a nanostructured superhydrophilic microlane Seungho Kim, Ho-Young Kim Deposition of functional liquids on solid surfaces is an important step in electronic circuit printing and fabrication of some biochips. Here we show that a liquid drop that gently touches a nanostructured superhydrophilic microlane surrounded by hydrophobic background spreads along the pre-defined pattern, allowing for a facile venue to liquid patterning. We find that different regimes of spreading dynamics occur depending on the lane width and the driving force at the liquid source. For a hydrophilic lane narrower than a critical width, the hemiwicking flow driven by capillarity but resisted by viscosity follows the Washburn law. For relatively wider lanes, on the other hand, the spreading rate is a sensitive function of the hydrostatic pressure at the liquid source, so that different power laws for spreading distance with time are observed. We rationalize the observed power laws with scaling analysis considering the effects of liquid bulk invading the hydrophilic lane. [Preview Abstract] |
Sunday, November 20, 2016 3:36PM - 3:49PM |
D37.00004: Fabrication of Janus hydrogels with stiffness gradient using drop coalescence Donghee Lee, Kale Golden, Sangjin Ryu The stiffness of the extracellular matrix (ECM) regulates cellular behaviors, and polyacrylamide (PAAM) gels with stiffness gradient have been used to simulate inhomogeneous ECM and to study the effects of the ECM stiffness on cells. Such hydrogel substrates with stiffness gradient can be fabricated with relatively complicated methods using microfluidics and moving masks. In our study, we develop a simpler method for fabricating Janus hydrogel which has a gradient of stiffness. Two prepolymer solutions were prepared for soft and stiff gel compositions, respectively, and one drop of each solution was placed on a hydrophobic patterned glass. Then, these two drops were gently squeezed by another glass being slowly lowered until coalescence, and gel polymerization was initiated after a certain time period for mixing. The motion of the drops was guided by the hydrophobic pattern. AFM nano-indentation showed that the fabricated Janus PAAM gels have a stiffness gradient which could be controlled by increasing mixing time. [Preview Abstract] |
Sunday, November 20, 2016 3:49PM - 4:02PM |
D37.00005: Optimum responses of droplets under electro-wetting actuation Tuan Tran, Quoc Vo The electro-wetting phenomenon has been used extensively to manipulate shape and position of liquid droplets in various applications such as microfluidics, microswitches, liquid lenses, light valves, and fast response displays. One of the quantities critically affecting the performance of such applications is the actuation time, defined as the duration for a droplet to reach a new equilibrium state after an electrical field is applied. We experimentally study the dynamical response of electro-actuated droplets for a wide range of control parameters including viscosity, drop size, and electric field. We show that there exists a relation between such parameters to achieve optimum actuation time, which can be validated by experimental data. [Preview Abstract] |
Sunday, November 20, 2016 4:02PM - 4:15PM |
D37.00006: Surface nanodroplets for highly efficient liquid-liquid microextraction Miaosi Li, Ziyang Lu, Haitao Yu, Xuehua Zhang Nanoscale droplets on a substrate are an essential element for a wide range of applications, such as laboratory-on-chip devices, simple and highly efficient miniaturized reactors for concentrating products, high-throughput single-bacteria or single-biomolecular analysis, encapsulation, and high-resolution imaging techniques. The solvent exchange process is a simple bottom-up approach for producing droplets at solid--liquid interfaces that are only several tens to hundreds of nanometers in height, or a few femtoliters in volume Oil nanodroplets can be produced on a substrate by solvent exchange in which a good solvent of oil is displaced by a poor solvent. Our previous work has significantly advanced understanding of the principle of solvent exchange, and the droplet size can be well-controlled by several parameters, including flow rates, flow geometry, gravitational effect and composition of solutions. In this work, we studied the microextraction effect of surface nanodroplets. Oil nanodroplets have been demonstrated to provide highly-efficient liquid-liquid microextraction of hydrophobic solute in a highly diluted solution. This effect proved the feasibility of nanodroplets as a platform for preconcentrating compounds for in situ highly sensitive microanalysis without further separation. Also the long lifetime and temporal stability of surface nanodroplets allow for some long-term extraction process and extraction without addition of stabilisers. [Preview Abstract] |
Sunday, November 20, 2016 4:15PM - 4:28PM |
D37.00007: Visualization of the Cassie--Wenzel transition with X-ray microscopy Su Jin Lim, Yeseul Kim, Suyeon Jeong, Changhyun Pang, Byung Mook Weon Water droplets on hydrophobic surfaces with micropillar usually exhibit two wetting states: (i) the Cassie state when air is trapped between water and micropillars and (ii) the Wenzel state when air is completely replaced by water. A transition from the Cassie to the Wenzel states is essential in designing stable hydrophobic surfaces. Directly visualizing the Cassie-Wenzel (C-W) transition is difficult with conventional microscopies because of no transparency from micropillars. Here we suggest a powerful technique based on high-resolution high-penetration X-ray microscopy for clearly visualizing the C-W transition. Thanks to the X-ray penetrating into the opaque micropillars, we were able to directly explore the intermediate state during the C-W transition. We study on the transition dynamics regarding how air replacement by water was gradually propagated with position and time. We believe that the replacement dynamics would be explained as a kind of phase transition kinetics. [Preview Abstract] |
Sunday, November 20, 2016 4:28PM - 4:41PM |
D37.00008: Direct measurements of the pressure distribution along the contact area during droplet impact Thanh-Vinh Nguyen, Kiyoshi Matsumoto, Isao Shimoyama We report direct measurements of the pressure distribution on the contact area during the impact of a droplet on a micropillar array. The measurements were realized using an array of MEMS-based force sensors fabricated underneath the micropillars. We show that immediately after the droplet hits the surface, the pressure becomes maximum at the center of the contact area and this maximum pressure value is more than 10 times larger than the dynamic pressure. This result emphasizes the effect of water-hammer-type pressure during the early stage of the impact. Furthermore, our measurement results demonstrate that the critical pressure associated with Cassie-Wenzel transition agrees well with the maximum capillary pressure of the micropillar array. [Preview Abstract] |
Sunday, November 20, 2016 4:41PM - 4:54PM |
D37.00009: Compound Droplet Levitation for Lab-on-a-Chip James Black, G. Paul Neitzel A fluid transport mechanism utilizing thermocapillarity has been previously shown to successfully levitate and translate both microliter- and nanoliter-volume droplets of silicone oil. The surface flow required to drive levitation and transport has not been achieved for aqueous droplets, and encapsulation of samples within a layer of silicone oil is necessary. A droplet-on-demand generator capable of producing nanoliter-volume compound droplets has been developed and previously reported. The work presented here discusses efforts to demonstrate the applicability of this microfluidic transport mechanism to lab-on-a-chip systems. We elaborate on translation speeds of single-phase, nanoliter-volume, silicone-oil droplets. Compound droplets of varying compositions of oil and water are then generated, captured, levitated, and merged to explore the composition limits thereof. [Preview Abstract] |
(Author Not Attending)
|
D37.00010: Pore-scale modeling of moving contact line problems in immiscible two-phase flow Alec Kucala, David Noble, Mario Martinez Accurate modeling of moving contact line (MCL) problems is imperative in predicting capillary pressure vs. saturation curves, permeability, and preferential flow paths for a variety of applications, including geological carbon storage (GCS) and enhanced oil recovery (EOR). Here, we present a model for the moving contact line using pore-scale computational fluid dynamics (CFD) which solves the full, time-dependent Navier-Stokes equations using the Galerkin finite-element method. The MCL is modeled as a surface traction force proportional to the surface tension, dependent on the static properties of the immiscible fluid/solid system. We present a variety of verification test cases for simple two- and three-dimensional geometries to validate the current model, including threshold pressure predictions in flows through pore-throats for a variety of wetting angles. Simulations involving more complex geometries are also presented to be used in future simulations for GCS and EOR problems. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [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