Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session A33: Drops: Evaporation |
Hide Abstracts |
Chair: François Boulogne, Princeton University Room: Ballroom A |
Sunday, November 22, 2015 8:00AM - 8:13AM |
A33.00001: Drying of a coffee drop: differences between dry and wet tables? Fran\c{c}ois Boulogne, Fran\c{c}ois Ingremeau, Howard Stone We have all experienced that a coffee drop drying on a table leaves a ring stain. The radial flow in the drop coupled with a larger drying flux at its edge are the reasons for the particle accumulation in the liquid wedge. However, if the substrate is wet, the liquid surrounding the drop modifies the vapor distribution, and thus the drop evaporation dynamics. Our experimental observations show that the drying kinetics and the particle motion are affected by the ambient conditions. We rationalize our experimental findings with a model that describes the spatially varying evaporation as well as the temporal evolution of the particles forming the ring. We believe that these results are of practical interest for printing applications involving multiple drop systems or drying surfaces. [Preview Abstract] |
Sunday, November 22, 2015 8:13AM - 8:26AM |
A33.00002: Evaporation of sessile droplets on smooth and structured substrates Pierre Colinet, Marie Flandroy, Sam Dehaeck, Alexey Rednikov, Benjamin Sobac, Yannis Tsoumpas Evaporation of sessile droplets remains a topic of active research nowadays, not only due to its widespread occurrence both in nature and technology, but also because it raises a number of interesting fundamental questions. Among these, the influence of the substrate topography is far from being understood. In this presentation, we focus on the difference between droplet evaporation dynamics on a smooth substrate and on substrates with controlled geometrical heterogeneities (square or hexagonal arrays of cylindrical pillars). While the wetting dynamics of droplets on such structured substrates has already been studied (in particular it is known that the droplet shape typically tends to adopt the symmetry of the pattern it lies upon), the influence the structure has on the evaporation dynamics (including the influence of pinning) has not yet received much attention. From interferometric measurements of droplet shapes, we highlight in particular that the evaporation from structured substrates is generally faster than on smooth substrates, and that the scaling exponents characterizing the evolution of radius versus time are also different. Pinning is also shown to be favored above a certain surface fraction of pillars, both for hexagonal and square arrays. [Preview Abstract] |
Sunday, November 22, 2015 8:26AM - 8:39AM |
A33.00003: Coffee-ring effect beyond the dilute limit Jin Young Kim, Seul-a Ryu, Hyungdae Kim, Joon Heon Kim, Jung Su Park, Yong Seok Park, Jeong Su Oh, Byung Mook Weon The coffee-ring effect, which is a natural generation of outward capillary flows inside drying coffee drops, is valid at the dilute limit of initial solute concentrations. If the solute is not dilute, the ring deposit is forced to have a non-zero width; higher initial concentration leads to a wider ring. Here we study the coffee-ring effect in the dense limit by demonstrating differences with various initial coffee concentrations from 0.1{\%} to 60{\%}. The coffee drops with high initial concentrations of real coffee particles show interesting evaporation dynamics: dense coffee drops tend to evaporate slowly. This result is different from the classic coffee-ring effect in the dilute limit. We suppose that the slow evaporation of dense coffee drops is associated with the ring growth dynamics. The coffee-ring effect becomes more significant in modern technologies such as self-assembly of nanoparticles, ink-jet printing, painting and ceramics. The complexity in evaporation dynamics of colloidal fluids would be able to be understood by expanding the coffee-ring effects in the dilute as well as the dense limits. [Preview Abstract] |
Sunday, November 22, 2015 8:39AM - 8:52AM |
A33.00004: Coffee ring effect resulted conductive nanowire patterns by evaporating colloidal suspension droplets without sintering process Xiaofeng Wang, Baekhoon Seong, Hadi Teguh Yudistira, Doyoung Byun Drying colloidal suspensions containing non-volatile solute will form a ring like pattern, which is called ``coffee ring effect.'' Here, we present the coffee ring effect with silver nanowires dispersing into DI water, resulting in a highly dense-packed nanowire ring patterns. The effect of nanowire length, concentration, droplet size, and substrate temperature were investigated. With shorter nanowires, a distinct ring could be obtained. Meanwhile, the concentration of the colloidal suspension was found to affect the ring width. The droplet size and nanowire length played a significant role in affecting the occurrence of the coffee ring effect. When smaller droplets (i.e., less than 150 $\mu $m) containing long nanowires ($\sim$ 20 $\mu $m), the coffee ring effect was suppressed. While smaller droplets containing short nanowires ($\sim$ 1 $\mu $m), the coffee ring effect was not affected. By increasing the temperature of the substrate, multi-ring pattern was formed inside the original ring. The resistivity of the semi-circle of the nanowire ring was measured, and had a minimum value of 1.32 $\times$ 10-6 $\Omega $m without any sintering process. These findings could be exploited to basic study of ring stain effect as well as the practical use, such as evaporative lithography and ink-jet printing for conductive film and display. [Preview Abstract] |
Sunday, November 22, 2015 8:52AM - 9:05AM |
A33.00005: Dependence of fluid flows in an evaporating sessile droplet on the characteristics of the substrate Lev Barash Temperature distributions and the corresponding vortex structures in an evaporating sessile droplet are obtained by performing detailed numerical calculations. A Marangoni convection induced by thermal conduction in the drop and the substrate is demonstrated to be able to result not only in a single vortex, but also in two or three vortices, depending on the ratio of substrate to fluid thermal conductivities, on the substrate thickness and the contact angle. The ``phase diagrams'' containing information on the number, orientation and spatial location of the vortices for quasistationary fluid flows are presented and analysed. The results obtained demonstrate that the fluid flow structure in evaporating droplets can be influenced in a controlled manner by selecting substrates with appropriate properties. [Preview Abstract] |
Sunday, November 22, 2015 9:05AM - 9:18AM |
A33.00006: Dynamics of surfactant-laden evaporating droplets George Karapetsas, Kirti Chandra Sahu, Omar K. Matar We consider the flow dynamics of a thin evaporating droplet in the presence of an insoluble surfactant and small particles in the bulk. Evolution equations for the film height, the interfacial surfactant and bulk particle concentration are derived using a lubrication model coupled by a constitutive relation for the dependence of the viscosity on local particle concentration. An important ingredient of our model is that it takes into account the fact that the surfactant adsorbed at the surface hinders the evaporation. Time-dependent simulations are performed to determine how the presence of surfactants affects the evaporation and flow dynamics with and without the presence of particles in the bulk. We discuss the various mechanisms that affect the shape of the droplet as it evaporates as well as the resulting pattern of particle deposition. [Preview Abstract] |
Sunday, November 22, 2015 9:18AM - 9:31AM |
A33.00007: On thin evaporating drops: when is the $d^2$-law valid? Matthew Saxton, Jonathan Whiteley, Dominic Vella, James Oliver We study the evolution of a thin, axisymmetric, partially wetting drop as it evaporates. The stress singularity at the contact line is regularized using slip and we perform a matched-asymptotic analysis in the limit of small slip. A generalization of Tanner's law to account for the effect of mass transfer is derived and the behaviour of the drop close to extinction is analysed. We find a criterion for when the contact-set radius close to extinction evolves as the square-root of the time remaining until extinction --- the famous $d^2$-law. However, for a sufficiently large rate of evaporation, our analysis predicts that a `$d^{13/7}$-law' should be more appropriate. Our asymptotic results are validated by comparison with numerical simulations. [Preview Abstract] |
Sunday, November 22, 2015 9:31AM - 9:44AM |
A33.00008: Evaporation of a drop on a periodic solid substrate with moving contact-line Amirhossein Amini, George. M. Homsy Experiments on evaporating droplets on structured surfaces have shown that the contact line does not move with constant speed, but rather in a step-like, ``stick-slip" fashion. As a first step in understanding this phenomenon, we study the evolution of a 2D incompressible Newtonian droplet evaporating on a non-flat substrate. We deploy a standard one-sided model which, together with the lubrication approximation, results in an evolution equation for the local height of the droplet. This is solved numerically for the case of constant fixed contact angle by utilizing numerical slip. We present results for sinusoidal substrates of different dimensionless amplitudes and wavelengths, with the droplet profile, evaporative mass flux and contact-line position evaluated for each case. In contrast with our previous results for a flat substrate, for which the contact line recedes in a nearly constant speed, we observe that the contact line speed and position show significant time variation, with the contact line moving approximately in a step-like fashion for relatively steep substrates. [Preview Abstract] |
Sunday, November 22, 2015 9:44AM - 9:57AM |
A33.00009: Evaporation dynamics of non-spherical sessile drops of pure fluids and binary mixtures Pedro J. Saenz, Omar K. Matar, Khellil Sefiane, Prashant Valluri, Jungho Kim The dynamics of pure axisymmetric volatile sessile droplets have been meticulously examined over the last four decades but remain poorly understood. Studies focusing on more realistic non-spherical configurations are virtually non-existent. The dynamics of the latter are examined in this investigation by means of experiments and numerical simulations. We show that the lifetime and bulk flow characteristics of these drops depend on their size and shape. The irregular geometries lead to the emergence preferential convection currents in the liquid as well as differential local evaporation rates noticeable along the contact line. Similarly, we inspect the thermocapillary stability of the flow, which results as the liquid volatility increases, and find that this is also affected by the non-uniform wettability along the triple line. The Marangoni-driven instabilities grow in an intricate spatio-temporal fashion leading to the emergence of different flow regimes. Finally, we also provide new insights into the evaporation process of binary-mixture drops. [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