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 M10: Drops: Laden with ParticlesDrops Particles
|
Hide Abstracts |
Chair: Samantha McBride, Massachusetts Institute of Technology Room: 503 |
Tuesday, November 21, 2017 8:00AM - 8:13AM |
M10.00001: Impact of a concentrated suspension drop Loren Jorgensen, Yoel Forterre, Henri Lhuissier We study the deformation of a suspension drop, made of non-Brownian spherical beads suspended in a Newtonian liquid, upon impact onto a flat solid surface. We focus on the range of large particle volume fractions (50\% $\lesssim \phi \lesssim$ 64\%), extending both below and above the critical volume fraction $\phi_c$, at which the steady viscosity diverges, and which also separates the dilatational and contractile responses of a sheared bead pile. Over this range, the drop deformation, as quantified by the maximal contact area with the surface, shows two different trends. For fixed impact conditions, the maximal area decreases with increasing $\phi$ up to a critical volume fraction $\phi^\ast$, above which it saturates. We will discuss how this maximal deformation depends on the suspending liquid viscosity and the particle size, as well as the relation between $\phi^\ast$ and $\phi_c$, which we measure independently. [Preview Abstract] |
Tuesday, November 21, 2017 8:13AM - 8:26AM |
M10.00002: Deposit Structure for Particle-laden Droplets Targeted by Electrospray Aref Ghafouri, Timothy Singler, Xin Yong, Paul Chiarot A hybrid printing technique that combines electrospray atomization with inkjet printing provides unique capabilities for exploring transport creating nanoparticle deposits with controlled structures. In this research, we use electrospray to deliver dry nanoparticles to the interface of particle-laden sessile droplets. Upon evaporation of the target sessile droplet, the particles at the interface are mapped to the underlying substrate. Particle locations in the final deposit were observed separately by tagging the particles dispersed inside the droplet and at its interface with different fluorophores. As expected, surfactant-free particles inside the target droplet were transported to its (pinned) contact line, creating a ``coffee ring'' morphology in the final deposit. The transport and final location of the interfacial particles was highly dependent on the presence of surfactant in the electrosprayed solution. If surfactant was present, the interfacial particles were transported to the apex of the target droplet, forming a dense region at the center of the final deposit. If the electrosprayed solution was surfactant-free, the transport of the interfacial particles was arrested and they were distributed uniformly across the final deposit. Similar deposit morphologies were found when experimenting with various surfactants, including Tween and sodium dodecyl sulfate. These results highlight the important of Marangoni flow in governing the final deposit structure for hybrid printing. [Preview Abstract] |
Tuesday, November 21, 2017 8:26AM - 8:39AM |
M10.00003: Crystalline desiccation patterns and film break up from evaporating drops on hydrophobic oxide surfaces Samantha McBride, Susmita Dash, Sami Khan, Kripa Varanasi Solute-laden sessile drops evaporating on a substrate will often force crystallization of the solute at the triple phase contact line between the drop, substrate, and air in an effect similar to the ``coffee-ring'' deposition of particles from a particle-laden drop. We report new observations of ring-shaped desiccation patterns of gypsum crystals on hydrophobic oxide substrates; ceria, erbia, and silica. These surfaces have similar contact angles (\textasciitilde 105 degrees), and evaporation of sessile drops proceeds at the same rate and without contact angle hysteresis on all three substrates. However, despite the apparent similarity, the patterns of crystal deposits exhibit large differences across the substrates. The supersaturation and elapsed time at the onset of crystallization also varied across substrates, despite overall evaporation rates being identical. The differences in patterns can be explained in light of the position and morphology of the crystals just prior to completion of evaporation when the sessile drop has transitioned to a thin film spread over the deposit area. Break-up of this film occurs very differently on the different surfaces, and is simultaneously influenced by existing crystals while also influencing final crystalline patterns. [Preview Abstract] |
Tuesday, November 21, 2017 8:39AM - 8:52AM |
M10.00004: Self-sorting of bi-dispersed colloidal particles near contact line of an evaporating sessile droplet. Rajneesh Bhardwaj, Nagesh Patil, Atul Sharma Self-sorting of bi-dispersed micrometer and sub micrometer polymer particles near the contact line of an evaporating sessile water droplet is investigated on non-heated and heated silicon wafer. On the non-heated silicon, a hilly accumulation of particles forms after droplet drying due to the early depinning of the contact line, while on the heated silicon, self-sorting at the contact line is observed within the ring at the contact line. SEM images reveal morphology of sorted patterns of bi-dispersed colloids. The receding contact angle reduces due to substrate heating and it helps to forming a stagnation region developed by the Marangoni flow near the contact line [Patil et al., Langmuir, 32(45), 2016]. The sorting within the ring occurs due to curvature of liquid-gas interface and preferential deposition of smaller sized particles in the stagnation region as compared to the larger size particles. Our measurements show that there exists a critical particle-size ratio and substrate temperature to achieve the sorting. The experimental results are compared with a mechanistic model. [Preview Abstract] |
Tuesday, November 21, 2017 8:52AM - 9:05AM |
M10.00005: Clustering of particles and pathogens within evaporating drops Jaebum Park, Ho-Young Kim The evaporation of sessile suspension drops leads to accumulation of the particles around the pinned contact line, which is widely termed the coffee ring effect. However, the evaporation behavior of a liquid drop containing a small number of particles with the size comparable to the host drop is unclear yet. Thus, here we investigate the motion and spatial distribution of large particles within a sessile drop. The spherical particles cluster only when their initial distance is below a critical value, which is a function of the diameter and wettability of particle as well as the surface tension and size of the host drop. We rationalize such a critical distance for self-assembly based on the balance of the capillary force and the frictional resistance to sliding and rolling of the particles on a solid substrate. We further discuss the physical significance of this drop-mediated “Cheerios effect” in connection with the fate of pathogens residing in drops as a result of sneezing and coughing. [Preview Abstract] |
Tuesday, November 21, 2017 9:05AM - 9:18AM |
M10.00006: 3D Lattice Boltzmann-Brownian Dynamics Simulations of Nanoparticle Deposition in Evaporating Liquid Masses Mingfei Zhao, Xin Yong Nanoparticle deposition coupled to hydrodynamics plays important roles in materials printing and thin-film processing. Investigations of nanoparticle dynamics in evaporating colloidal dispersions could elicit a greater understanding of the processing-structure relationship for evaporation-induced self-assembly and deposition. A 3D free-energy lattice Boltzmann method combined with Brownian dynamics is developed to simulate evaporating colloidal droplets and rivulets. In this work, we explore the deposition on solid substrates with different wetting properties, namely static contact angle and contact line motion. We highlight the influence of convective flows on the assembly kinetics and deposit patterns using the developed model. We introduce a novel approach to impose a pinned contact line for most of droplet lifetime. The time evolutions of contact angle and droplet volume are examined to characterize the pinning scheme. We observe the process of nanoparticle self-assembly during the evaporation of droplets and rivulets and quantitatively analyze the deposit structure. [Preview Abstract] |
Tuesday, November 21, 2017 9:18AM - 9:31AM |
M10.00007: Life and death of a particle-laden liquid sheet Pascal Raux, Anthony Troger, Pierre Jop, Alban Sauret Thin films of suspensions are involved in many industrial processes, such as surface coating or liquid transport in tubes. For dilute suspensions, it is well known that the particles increase the effective viscosity. However, this only holds in the continuum approximation, and should fail in a confined situation such as a liquid sheet. Here, we investigate the dynamics of a thin film of suspension, formed upon the impact of a suspension drop. We show that the atomization process varies when the thickness of the liquid film is smaller than the particle’ size, leading to a loss of stability of the sheet. Our results highlight the influence of capillary effects in this confined flow. [Preview Abstract] |
Tuesday, November 21, 2017 9:31AM - 9:44AM |
M10.00008: Effect of particle wettability on the stick-slip motion of the contact line Dong-Ook Kim, Min Pack, Arif Rokoni, Paul Kaneelil, Ying Sun Contact line dynamics is crucial in determining the deposition patterns of evaporating colloidal drops. Using high-speed interferometry, we directly observe in real time the stick-slip motion of the contact line and instantaneous drop shape in inkjet-printed pico-liter colloidal drops containing nanoparticles of varying wettabilities. Integrated with optical profilometry, the instantaneous particle deposition rate may also be determined. The results show that the contact line stick-slip motion highly depends on the particle wettability. While the stick-slip motion is observed for the hydrophobic particle case, the contact line continues to depin in the hydrophilic case. A multi-ring deposition is found for the hydrophobic nanoparticles but not for the hydrophilic ones when keeping other parameters the same. This is consistent with the model prediction of the number of particles required to pin at the contact line based on force analysis and motion of particles near the contact line. Using the combined modeling and experiments, the relation between particle wettability, contact line motion, and final deposition morphology are obtained. [Preview Abstract] |
Tuesday, November 21, 2017 9:44AM - 9:57AM |
M10.00009: Development of local interfacial strains and stresses in the formation of asymmetric particle-stabilized capsules Shelley Anna, Charles Sharkey Particles adsorbed at fluid interfaces can stabilize bubbles and droplets against coalescence. However, the method of generating the interface strongly impacts interparticle interactions, and in turn, interfacial microstructure, rheology, and stability. By controlling the adsorbed concentration of particles via residence time in a long channel, we generate non-spherical capsules that retain their shape for at least tens of hours. The capsule shape is in part determined by the dynamics of the bubble as it exits the tube. In this talk, we use image analysis to examine the development of interfacial strains during capsule formation at the channel exit. Tracking the bubble radius profile as a function of time allows us to examine the evolution of interfacial area and bubble volume, as well as the dilation rate profile along the interface. These observations allow us to infer the development of interfacial dilational and buckling stresses that lead to the capsule shape stability. We compare the interfacial strain evolution for clean, surfactant, and particle-laden interfaces as a function of the composition of the interfacially active component. These observations provide a direct connection between colloidal and production factors, and interfacial mechanics and capsule stability. [Preview Abstract] |
Tuesday, November 21, 2017 9:57AM - 10:10AM |
M10.00010: Experimental study of droplet formation of dense suspensions Gustaf Martensson, Fabian Carson As with the jet printing of dyes and other low-viscosity fluids, the jetting of dense fluid suspensions is dependent on the repeatable break-off of the fluid filament into well-formed droplets. It is well known that the break-off of dense suspensions is dependent on the volume fraction of the solid phase, particle size and morphology, fluid phase viscosity et cetera, see for example van Deen et al. (2013). The purpose of this study is to establish a deeper understanding of the formation process of droplets of dense suspensions. Previous experiments have utilised a filament break-off device (FilBO) developed in-house. These experiments utilise an ejection device based on rapid volumetric displacement of the fluid through a conical nozzle. The suspension samples consist of a resin-based flux and spherical particles with diameters of \(d_p = 5-25 \mu \)m. A droplet of of the suspension with a volume of \(V_{\mathrm{drop}} = 2-50 \) nl is ejected from the nozzle. Correlations between droplet speed and the temporal development of the volumetric displacement will be presented. Further results relating break-off length and rate versus particle diameter, volume fraction and probe speed will be presented. [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