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 H35: Microscale Flows: Interfaces and Wetting |
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Chair: John Sader, The University of Melbourne Room: 617 |
Monday, November 25, 2019 8:00AM - 8:13AM |
H35.00001: DEM Modeling of Coupled Multiphase Flow and Granular Mechanics: Wettability Control on Fracture Patterns Yue Meng, Bauyrzhan Primkulov, Zhibing Yang, Fiona Kwok, Ruben Juanes The interplay between multiphase flow in a granular medium and the displacement of the grain particles generates a wide range of patterns. The balance between frictional, viscous, and capillary forces has been studied in experiments and simulations, and has helped understanding the underlying mechanisms for a wide range of phenomena, such as methane migration in lake sediments. Here we study fluid-induced fracturing of granular media by hydromechanically coupling a moving capacitor dynamic network model with discrete element modeling. We inject a less viscous fluid into a frictional granular pack initially saturated with a more viscous, immiscible fluid under low capillary number. We study the impact of contact angle and initial packing density, and find four different regimes of the fluid invasion morphology: cavity expansion and fracturing, frictional fingers, capillary invasion, and capillary compaction. We rationalize these simulation outputs by means of a jamming analysis, which allows us to explain fracture initiation as emerging from a jamming transition. We synthesize the analysis in the form of a novel phase diagram of jamming for wet granular media. [Preview Abstract] |
Monday, November 25, 2019 8:13AM - 8:26AM |
H35.00002: How the natural structure of cuttlebone facilitates efficient microfluidic transport Karl Frohlich, Ehsan Esmaili, Ting Yang, Ling Li, Sunghwan Jung When a viscous fluid is displaced by a less viscous fluid in a thin channel, the interface moves unevenly due to the Saffman–Taylor instability. Suppressing such instability plays a key role in many petroleum industries and biological systems. One natural example of this phenomenon is in the bones of cuttlefish. These cuttlebones contain multiple parallel microscopic chambers which are reinforced by winding vertical wall-like structures. It has been studied that the cuttlefish regulates its buoyancy by pumping water in and out of this structure. In this study, we investigate the cuttlebone structure for its unique ability to suppress the instability of a moving liquid-gas interface. Cuttlebone samples were studied in vitro to understand how fluid moves through the structure at different pressures and flow rates. Additionally by using cuttlebone structure as biological inspiration, we fabricated simplified channels using 3D resin printing in order to more rigorously test the impact of the liquid-gas meniscus at varying channel curvatures, pressures and other arrangements. Results show that a presence in channel curvature and positioning, like that seen in cuttlebone, can prevent the uneven growth of menisci, helping to transport a liquid-gas interface more uniformly. [Preview Abstract] |
Monday, November 25, 2019 8:26AM - 8:39AM |
H35.00003: Effect of Wetting on Pinch-off Dynamics of Viscoelastic Micellar Fluids Hadi Mohammadigoushki, Shijian Wu We conduct experiments by gradually depositing non-Newtonian surfactant fluids onto a horizontal solid substrate via a vertical needle. We investigate the extent to which, the spreading dynamics of the fluid contact-line on the solid substrate can affect the thinning dynamics of the fluid filament formed between the needle and substrate. Experiments are performed using two flat substrates; a big substrate, where fluid contact-line in free to move and a finite size substrate, where fluid contact-line is pinned. Two distinct flow regimes are observed. In regime I, the fluid wetting dynamics does not significantly affect the filament thinning process. However, in regime II, the fluid wetting on the big solid substrate impacts the filament thinning dynamics significantly by lowering the filament life time, extensional relaxation times and the Trouton ratios compared to that of the pinned contact-line. Our analysis shows that spreading of these viscoelastic surfactant fluids are reasonably well captured by Tanner's law suggested for spreading of a Newtonian fluid on solid substrates. We propose a scaling analysis based on a combination of the wetting forces and viscous dissipation that can successfully distinguish these two flow regimes from each other. [Preview Abstract] |
Monday, November 25, 2019 8:39AM - 8:52AM |
H35.00004: Surface dilatational rheology during phase coexistence of insoluble surfactants Harishankar Manikantan, Todd Squires Surfactants -- molecules and particles that preferentially adsorb to fluid interfaces -- play a ubiquitous role in industrial and biological flows involving fluid interfaces. Beyond reducing surface tension, surfactants may modify fluid flow by exerting Marangoni and/or surface rheological stresses. Additional complexities often arise when insoluble surfactants exhibit non-trivial morphologies, for example, forming condensed phases with liquid crystalline order that coexist with disordered phases. Here, we show that the dynamic growth of liquid crystalline domains at the expense of the continuous phase upon compression gives rise to a frequency-dependent viscoelastic behavior. We treat the dynamic `freezing' and `melting' of insoluble surfactant domains as a 2D analog of classic works on dynamic adsorption and desorption of soluble surfactants. Notably, our model predicts that liquid crystalline domains grow freely and the surfactant exerts no additional surface stresses upon asymptotically slow compression. However, rate-dependent surface elasticity and surface viscosity emerge when the compression rate is comparable to phase change rate. [Preview Abstract] |
Monday, November 25, 2019 8:52AM - 9:05AM |
H35.00005: ABSTRACT WITHDRAWN |
Monday, November 25, 2019 9:05AM - 9:18AM |
H35.00006: Size dependent droplet interfacial tension and surfactant transport in oily bilgewater systems Yun Chen, Cari Dutcher Many liquid-liquid emulsions, including shipboard oily bilge waters, are chemically stabilized by surfactants and additives. The emulsion stability is determined by the interfacial tension (IFT) of surfactant-laden interface between the continuous and dispersed phase, as well as the size of the dispersed droplets. In the present work, the dynamic IFT of droplets at micron-scale (\textasciitilde 80 um) and milli-scale (\textasciitilde 2 mm) is measured with simulated bilge waters with soluble surfactant systems. It is found that the IFT of micron-scale droplets decays faster than that of the milli-scale droplets due to smaller diffusion boundary layer thickness. When surfactants are added into aqueous phase for both water-in-oil and oil-in-water condition, the IFT of micron-scale droplets decays faster when the surfactant is in outer phase than in the inner phase. In contrast, for the larger milli-scale droplets, the IFT decay rate does not depend on which phase the surfactant is added. The observations are explained by the change in diffusion limited to kinetic limited surfactant transport as the droplet size decreases. In addition, experimental results of droplet coalescence depending on the IFT using model system is also presented in this work. [Preview Abstract] |
Monday, November 25, 2019 9:18AM - 9:31AM |
H35.00007: Characteristics of wetting distance in multilayered paper-based channel. Hyunwoong Kang, Ilhoon Jang, Simon Song A multilayered paper-based device which has a gap between paper layers can generate much greater flow velocity than a typical single layer paper-based device. This feature enables quick analysis in applications utilizing paper-based devices. Predicting the time to reach the detection point and the amount of sample fluid is critical to improving detection accuracy and manufacturing the multi-functional device. However, the multilayered paper-based device has a more complicated fluid flow than the conventional device resulting in the different flow with the single-layer device that can be described by the Lucas-Washburn equation. These are due to the simultaneous sample flow flowing through both gap and paper layer. For example, since the paper internal flow is much slower than the gap internal flow, the fluid can be absorbed into the paper layer in the thickness direction, and it reduces a flow rate, especially at the initial stage of the fluid flow. In this study, we analyze the characteristics of the flow mainly focused on the differences between the existing capillary driven flow model and explain the factors that affect the wetting distance in the multilayer paper-based channel. [Preview Abstract] |
Monday, November 25, 2019 9:31AM - 9:44AM |
H35.00008: Flow topology and bifurcations in streaming lattices Yashraj Bhosale, Tejaswin Parthasarathy, Giridar Vishwanathan, Gabriel Juarez, Mattia Gazzola Viscous streaming flows generated due to constant curvature objects (circular cylinders, infinite plates) have been well-understood in the past. Yet, characterization and understanding of such flows when multiple body length-scales are involved has not been looked into. We propose a simplified setting to understand and explore the effect of multiple curvatures on streaming flows, analysing the system through the lens of bifurcation theory. This analysis uncovers the dynamic richness of the system, which we showcase through potential microfluidic applications. [Preview Abstract] |
Monday, November 25, 2019 9:44AM - 9:57AM |
H35.00009: Thermal behavior of slip length in connection with fluid-solid chemical affinity Adriano Grigolo, Thiago Viscondi, Julio Meneghini, Iber\^{e} Caldas The relation between fluid slip on a solid surface and flow temperature is investigated with the help of molecular dynamics simulations. An atomistic Couette configuration, consisting of a Lennard-Jones fluid and two rigid walls, is prepared and evolved to its steady state, where the slip length can be readily extracted from the linear velocity profile. Simulations are carried out for a broad range of temperatures and for different magnitudes of the fluid-solid chemical affinity. This last parameter is found to affect the overall shape of the slip length vs. temperature curve. Depending on its value, three distinct types of thermal behavior are observed: slippery (unbounded and decreasing), critical (constant), and sticky (bounded and increasing). We find that the temperature dependence of the slip length in each of these cases is well described by a simple heuristic function, whose adjustable parameters have a clear physical interpretation. The present study is aimed at the development of material-specific boundary conditions and their use in multiscale simulations. In this context, our analysis, once extended to more complex substances, may aid in the design and optimization of microfluidic devices and nanostructured membranes set to operate at specific temperatures. [Preview Abstract] |
Monday, November 25, 2019 9:57AM - 10:10AM |
H35.00010: Existence of the Navier slip condition for liquids Jesse Collis, Selim Olcum, Debadi Chakraborty, Scott Manalis, John Sader The Navier slip condition is regularly used to characterize the interaction of a fluid with a solid boundary. Its use at the gas-solid boundary is justified rigorously from Boltzmann's kinetic theory of gases, however no such parallel exists at the liquid-solid boundary. The strongest evidence for existence of the Navier slip condition at the liquid-solid interface comes from molecular dynamics simulations. As dictated by kinetic theory, the Navier slip length is a constitutive property that holds when the flow is continuum away from the solid interface. Here, we present an experimental protocol that is used to measure the Navier slip length on individual and isolated particles with exquisite precision. Experiments consisting of thousands of measurements on individual gold nanoparticles give a constant slip length of 2.7$\pm$0.6 nm---independent of particle size---providing experimental validation of the Navier slip condition for liquids. [Preview Abstract] |
Monday, November 25, 2019 10:10AM - 10:23AM |
H35.00011: Surface acoustic wave driven wetting transition. Sudeepthi A, Ashis Kumar Sen, Leslie Yeo Water drop deposited on a nanostructured superhydrophobic surface undergoes wetting transition from Cassie-Baxter state to Wenzel state upon excitation by MHz frequency acoustic waves (surface acoustic waves). The wetting transition is governed by the competition between the input acoustic energy supplied to the drop via the surface acoustic waves (SAWs) and the energy barrier associated with the transition. The kinetic energy gained by the drop due to the transfer of energy from SAWs drive the liquid into the hydrophobic grooves to overcome the energy barrier associated with the replacement of low energy solid-gas interface with the high energy solid-liquid interface. As the liquid comes in contact with the substrate due to the filling of nanogrooves, boundary layer acoustic streaming assisted by the capillary flow in the hydrophilic bottom walled nanogrooves displaces the drop contact line giving rise to drop spreading. The transition is irreversible since the drop attains minimum energy state in the Wenzel condition. [Preview Abstract] |
Monday, November 25, 2019 10:23AM - 10:36AM |
H35.00012: In Situ Identification of Dewetting-Induced Large-Scale Deformation of Vertically Aligned Single-Walled Carbon Nanotubes Yuta Yoshimoto, Koichi Isomura, Sou Sugiyama, Hua An, Takuma Hori, Taiki Inoue, Shohei Chiashi, Shu Takagi, Shigeo Maruyama, Ikuya Kinefuchi We investigated dynamical processes of capillary-mediated deformation of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) via {\it in situ} observation of their wetting and dewetting behaviors using an environmental scanning electron microscope. Three types of wetting behaviors on a VA-SWCNT sample were observed, namely conical shaped water aggregates, spherical droplets on tips of conical shaped water aggregates, and extensively distributed water layers. The former two types both resulted in dimples on the VA-SWCNT surface, failing to induce large-scale deformation of VA-SWCNTs. In contrast, the latter caused the formation of wall-like structures and crack propagation in the VA-SWCNT film during the dewetting process due to directional retraction of vapor-liquid interfaces. Compared to the previous studies based on {\it ex situ} observations of dried samples, our {\it in situ} observation successfully captured temporal evolution of the dewetting-induced deformation, which represents initial stages of capillary processes that lead to the self-organization of VA-SWCNTs reported in recent literatures. [Preview Abstract] |
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