Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E11: Drops: Complex FluidsDrops
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Chair: Elaheh Alizadeh-Birjandi, University of California, Los Angeles Room: 504 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E11.00001: Lateral Migration and Equilibrium of Compound Drops in Low Reynolds Number Poiseuille Flow Sangkyu Kim, Sadegh Dabiri The migration and equilibrium of monodisperse compound drops in a channel with rectangular cross-section are numerically investigated at droplet Reynolds number Re = O(1) and Capillary number Ca = O(0.1) with varying size ratio between the compound drop diameter and the channel size, aspect ratio of the channel, radii ratio between the inner and outer drops, and initial placement. The compound drops' outer diameter is between half the width and half the height of the channel, and three equilibrium configurations without centerline symmetry are found; two with symmetry about the longer direction, and one about the shorter direction. In the former two cases, the point of maximum velocity within the channel lies inside the compound drop, and two counter-rotating circulations are created inside the outer drop. Which circulation the inner drop resides within depends on the radii ratio and the initial placement, and is correlated to the equilibrium configuration. In the latter case, the compound drop reaches a stable equilibrium away from the centerline with a single circulation inside the outer drop. The initial placement of the compound drop is mostly inconsequential, as this configuration is preferred given an initial lack of symmetry about the longer wall direction. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E11.00002: Experimental Investigation of Extensional Deformation of Immiscible Droplets in a Laminar, Converging Flow Aditya Sangli, Marcelo Arispe-Guzman, Connor Armstrong, David Bigio The deformation of an immiscible droplet in an extensional flow has been widely studied by researchers using experimental four-roll mills where the bulk liquid imposes a stagnation extensional deformation on the droplet. However, it is of vital interest to study the behavior of an immiscible droplet in a non-stagnant extensional flow which can be produced using a converging channel. A hyperbolic converging channel was built, which could produce a constant extensional rate in the center of the channel, and deformation of droplets of Castor oil injected in a matrix of Silicone oil was observed. Droplets injected in the center of the channel experienced a pure extensional deformation while the droplets injected at an offset position attained the affine state. The nature of the droplet deformation and the critical Capillary numbers are compared with the four-roll mill experiments. Additional experiments were performed with the initial position of the droplet being vertically off center. Higher strain rates were exhibited compared to the pure extensional flow condition. An analysis of the flow field helps explaining the phenomenon and provides insight into the droplet behavior. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E11.00003: An Evaporating Ouzo Drop on a Superamphiphobic Surface Huanshu Tan, Christian Diddens, Michel Versluis, Hans-J\"{u}rgen Butt, Xuehua Zhang, Detlef Lohse The Greek drink Ouzo (or Pastis or Raki) is a miscible solution and primarily consists of water, ethanol and anise oil. Recently, we discovered how the preferential evaporation of ethanol triggers the “ouzo effect”, i.e. the spontaneous nucleation of oil microdroplets, in an evaporating ouzo drop [PNAS 113, 8642–8647 (2016)]. In this work, we performed evaporation experiments on a superamphiphobic, which is both superhydrophobic and superoleophobic, to achieve low wettability for the ouzo drops. The ouzo drops initially hold a large static contact angle (larger than 150$^{\circ}$). Thus the singularity at the three phase contact line is absent. Codetermined by the evaporation flux distribution and volatility difference between water and ethanol, the evaporation-triggered ouzo effect preferentially occurs at the apex of the drop. During the evaporation process, two distinct slopes characterize the volume decrease of the drop. Theoretically, based on Popov’s diffusion model for quasi-steady natural evaporation of pure liquid drops, we propose an approximate diffusion model for the drying characteristics of ouzo drops with more than one component. The generalized diffusion model predicts the evaporation of the drops in agreement with experiment and numerical simulation results. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E11.00004: Roughness influence on human blood drop spreading and splashing Fiona Smith, Naomi Buntsma, David Brutin The impact behaviour of complex fluid droplets is a topic that has been extensively studied but with much debate. The Bloodstain Pattern Analysis (BPA) community is encountering this scientific problem with daily practical cases since they use bloodstains as evidence in crime scene reconstruction. We aim to provide fundamental explanations in the study of blood drip stains by investigating the influence of surface roughness and wettability on the splashing limit of droplets of blood, a non-Newtonian colloidal fluid. Droplets of blood impacting perpendicularly different surfaces at different velocities were recorded. The recordings were analysed as well as the surfaces characteristics in order to find an empirical solution since we found that roughness plays a major role in the threshold of the splashing/non-splashing behaviour of blood compared to the wettability. Moreover it appears that roughness alters the deformation of the drip stains. These observations are key in characterising features of drip stains with the impacting conditions, which would answer some forensic issues. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E11.00005: Deposition dynamics of multi-solvent bioinks Paul Kaneelil, Min Pack, Chunxiao Cui, Li-Hsin Han, Ying Sun Inkjet printing cellular scaffolds using bioinks is gaining popularity due to the advancement of printing technology as well as the growing demands of regenerative medicine. Numerous studies have been conducted on printing scaffolds of biomimetic structures that support the cell production of human tissues. However, the underlying physics of the deposition dynamics of bioinks remains elusive. Of particular interest is the unclear deposition dynamics of multi-solvent bioinks, which is often used to tune the micro-architecture formation. Here we systematically studied the effects of jetting frequency, solvent properties, substrate wettability, and temperature on the three-dimensional deposition patterns of bioinks made of Methacrylated Gelatin and Carboxylated Gelatin. The microflows inside the inkjet-printed picolitre drops were visualized using fluorescence tracer particles to decipher the complex processes of multi-solvent evaporation and solute self-assembly. The evolution of droplet shape was observed using interferometry. With the integrated techniques, the interplay of solvent evaporation, biopolymer deposition, and multi-drop interactions were directly observed for various ink and substrate properties, and printing conditions. Such knowledge enables the design and fabrication of a variety of tissue engineering scaffolds for potential use in regenerative medicine. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E11.00006: Marangoni bursting Etienne Reyssat, Ludovic Keiser, Hadrien Bense, Pierre Colinet, José Bico At the surface of a sunflower oil bath, a drop of water adopts a lenticular shape. Conversely, alcohol totally wets the oil and spreads. Depositing a mixture of water and alcohol reveals a spectacular fragmentation phenomenon. If it contains enough alcohol, the drop spontaneously spreads and fragments into a myriad of minute droplets whose size strongly depends on the initial mixture composition. Marangoni flows resulting from the differential evaporation of alcohol and water play a key role in this self-emulsification process. The intricate coupling of hydrodynamics, wetting and evaporation is well captured by analytical scaling laws that predict the characteristic radius and timescale of spreading. Other combinations of liquids also lead to this fascinating phenomenon and further confirm our scenario. [Preview Abstract] |
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