Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session P36: Microscale Flows: Moving Contact Line and Thin Film Evaporation |
Hide Abstracts |
Chair: Serafim Kalliadasis, Imperial College London Room: 618 |
Monday, November 25, 2019 5:16PM - 5:29PM |
P36.00001: The disparity between thermodynamic and mechanical surface tension in the vicinity of the moving contact line Joseph Thalakkottor, Kamran Mohseni Thermodynamic and mechanical surface tensions are commonly assumed to be equal. Here, we shall show that this is not the case in the vicinity of the moving contact line. In the vicinity of the moving contact line, the stress in the bulk fluid increases rapidly, which we shall show is accompanied by a corresponding increase in surface dilatation rate. We demonstrate that this non-zero rate of surface dilatation results in a disparity between thermodynamic and mechanical surface tension. Considering that surface tension can be interpreted as surface pressure, it is shown that this deviation between mechanical and thermodynamic surface tension is analogous to pressure in bulk fluid, where thermodynamic and mechanical pressures are not necessarily equal for a compressible fluid. We present these findings via molecular dynamics simulations of a forced wetting problem and demonstrate that the surface dilatation rate plays an important role in capturing the difference in dynamic and static contact angles. [Preview Abstract] |
Monday, November 25, 2019 5:29PM - 5:42PM |
P36.00002: Dynamic contact angle under unfavorable viscosity contrast. Bauyrzhan Primkulov, Jane Y. Y. Chui, Amir A. Pahlavan, Ruben Juanes The current view of dynamic contact angle is encapsulated in the seminal experiments of Hoffman from the 1970s. He displaced air with a viscous liquid inside a capillary tube. By varying the wetting properties of the liquid and the liquid's viscosity and injection rate, he determined a relation between the dynamic contact angle and the static contact angle, now known as Cox-Voinov relation. Very little is known, however, about the dynamics of the contact line in the reverse scenario: when a more viscous liquid is displaced by a less viscous fluid. We fill this gap with a series of experiments in capillary tubes, and analyze theoretically the striking deviation from the Cox-Voinov relation. Finally, we point out several practical applications, from spin-coating of capillary tubes to fluid displacement in porous media. [Preview Abstract] |
Monday, November 25, 2019 5:42PM - 5:55PM |
P36.00003: Dry spot growth dynamics during thin film evaporation on hierarchical surfaces. Arif Rokoni, Dong-Ook Kim, Lige Zhang, Fausto Pasmay, Ying Sun The topography of structured surfaces plays a significant role in increasing the critical heat flux (CHF) during thin film evaporation by enhancing capillary-assisted liquid delivery to the evaporating thin film region. As the CHF is reached, evaporation becomes dominant, leading to the formation of dry spots. In this study, the contact line dynamics during dry spot growth is investigated for thin film evaporation on hierarchical micro/nanostructured surfaces with ZnO nanorods grown on silicon micropillars of varying spacings and heights. Using laser reflection interference microscopy, the 3D meniscus shape at the micropillar level and the contact line dynamics at two length scales are directly captured. Nanoscale receding front is found ahead of bulk receding during dry spot growth on hierarchical surfaces, where the bulk receding front follows a two-stage motion, slower around the micropillars and faster in-between pillars. This nanoscale precursor film, due to the presence of nanorods, contributes significantly to the evaporative heat flux. The detailed understanding of dry spot growth dynamics sheds light on more effective designs of hierarchical surfaces for CHF enhancement. [Preview Abstract] |
Monday, November 25, 2019 5:55PM - 6:08PM |
P36.00004: Novel humidity responsive film fabricated by hydrophilic nanostructured titanium oxide Minki Lee, Gyuhyeon Han, Jinkee Lee We fabricated a humidity responsive film comprising a bundle of titanium oxide tubes that changes film's curvature corresponding to the relative humidity. The mechanism of the change in curvature of the film can be explained by adsorption, condensation, and evaporation of water molecules within the surface of film. During adsorption, a liquid bridge forms because of growth of a water layer between tubes, thus contracting the gab between tubes. When vapor pressure exceeds the equilibrium vapor pressure, condensation occurs at the meniscus of the liquid bridge, thus expanding the gap between tubes. We obtained the adsorption and desorption isotherms for the humidity responsive film by measuring physical adsorption. Additionally, we demonstrated varying motions of the humidity responsive film when a water droplet was applied on the surface. The film could distinguish between saturated and oversaturated humidity conditions, such as fog and rain, respectively. Therefore, this humidity responsive film can be applied to environmental monitoring systems and possibly even to energy harvesting systems. [Preview Abstract] |
Monday, November 25, 2019 6:08PM - 6:21PM |
P36.00005: Capillary Flow with Evaporation in Open Rectangular Microchannels Panayiotis Kolliopoulos, Krystopher Jochem, Robert Lade, Lorraine Francis, Satish Kumar Numerous applications rely upon capillary flow in microchannels for successful operation including lab-on-a chip devices, porous media flows, and printed electronics manufacturing. We develop a Lucas-Washburn-type model that incorporates the effects of concentration-dependent viscosity and evaporation on capillary flow in open channels having rectangular cross section. In the absence of evaporation, prior studies have demonstrated better agreement between model predictions and experimental observations in low-viscosity liquids when using a no-slip rather than a no-stress boundary condition at the upper liquid-air interface. However, flow visualization experiments conducted in this work suggest the absence of a rigidified liquid-air interface. The use of the no-stress condition results in overestimation of the time evolution of the liquid front due to underestimation of viscous forces by the model. Model predictions are also compared to prior experiments in the presence of evaporation. Scaling relationships obtained from the model for the dependence of the final liquid-front position and total flow time on the channel dimensions and rate of uniform evaporation are found to be in good agreement with experimental observations (Kolliopoulos et al., Langmuir 35 (2019) 8131). [Preview Abstract] |
Monday, November 25, 2019 6:21PM - 6:34PM |
P36.00006: Capillary Flow of Gallium Based Liquid Metal with Surface Oxide Sangyun Jung, Sejin Choi, Jongwon Lee, Wonjung Kim Gallium-based liquid metals are attracting growing interest thanks to their potential applications in flexible electronic devices. The liquid metals are non-toxic and highly electrically conductive while the state of liquid at a room temperature allows exclusively large deformations. The liquid metals typically form a surface oxide layer in the atmosphere leading to solid-like behavior, and their flow often exhibits unpredictable and complex characteristics. To better understand the effects of the oxide layer of gallium-based liquid metals on flow, we experimentally investigate liquid metal flow in a capillary tube and analyze the forces acting on the interface with the oxide skin. [Preview Abstract] |
Monday, November 25, 2019 6:34PM - 6:47PM |
P36.00007: Transitions between motion regimes of the three phase contact line during the pattern deposition of polymer from a volatile solution Ofer Manor, Mohammad Abo Jabal, Anna Zigelman We investigate the deposition of polymer from a volatile solution. The interplay between different transport mechanisms in the volatile solution determines the motion regime of the three phase contact line and hence the morphology of the deposit. We observe monotonous slip, stick-slip, and periodic wetting-dewetting motions of the contact line. The deposits take the form of continuous coating in the former case and parallel stripes in the two later cases. To investigate transitions between the different motion regimes, we evaporate solutions of Poly-methyl-methacrylate and Poly-dimethyl-siloxane in toluene. The transitions between particular motion regimes of the contact line are connected to two types of competitions between physical mechanisms. A transport competition between polymer diffusion and convection determines the distribution of polymer in the volatile meniscus and hence determines the distribution of spatial variations in the excess energy at the free surface of the solution. A competition between evaporative and surface energy stresses in the liquid meniscus determines the motion of the contact line. We report the temporal variations of the contact line position during each motion regime and use theory to validate our experimental findings. [Preview Abstract] |
Monday, November 25, 2019 6:47PM - 7:00PM |
P36.00008: The resolution of the moving contact line problem Serafim Kalliadasis At the heart of the problem is its multiscale nature: a nanoscale region close to the solid boundary where the continuum hypothesis breaks down must be resolved before phenomenological macroscale parameters such as contact line friction and slip, often adopted to alleviate the singularity, can be obtained. Here we will review recent progress made by our group to rigorously analyse the moving contact line problem and related physics from the nano- to macroscopic lengthscales. Specifically, to capture nanoscale properties and to establish a link to the macroscale behaviour, we employ elements from the statistical mechanics of classical fluids, namely density-functional theory (DFT). We formulate a new and general dynamic DFT (DDFT) which is coupled to hydrodynamics and we refer to as ``hydrodynamic DDFT''. It is inherently multiscale bridging the micro- to the macroscale and retaining the relevant fundamental microscopic information (fluid temperature, fluid-fluid and wall-fluid interactions) at the macroscopic level. Work analysing the contact line in both equilibrium and dynamics will be presented. Hydrodynamic DDFT allows us to benchmark existing phenomenological models and reproduce some of their key ingredients. But its multiscale nature also enables us to unravel the underlying physics of the moving contact line, not possible with any of the previous approaches, and indeed show that the physics is much more intricate than the previous models suggest. [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