skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: HYDRODYNAMICALLY-INDUCED DROPLET MICROVORTICES FOR CELL PAIRING APPLICATIONS
We present a water-in-oil droplet microfluidic trap array capable of modulating the distance between co-encapsulated cell pairs through microvortex formation. We demonstrate that vortex shape and periodicity can be directly controlled by the continuous phase flow rate. Explicit equations for the recirculation time inside droplet microvortices were derived by approximating the velocity fields through analytic solutions for the flow inside and outside of a spherical droplet. Comparison of these expressions against Particle Tracking Velocimetry (PTV) measurements of K562 (leukemia) cells circulating inside 50 μm droplets showed excellent theoretical agreement.  more » « less
Award ID(s):
1841509
PAR ID:
10316888
Author(s) / Creator(s):
Date Published:
Journal Name:
25th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2021)
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Journal of Fluid Mechanics)
    null (Ed.)
    In this paper, we theoretically investigate the migration of a surfactant covered droplet in a Poiseuille flow by including the surface viscosities of the droplet. We employ a regular perturbation expansion for low surface Péclet numbers and solve the problem up to a second-order approximation. We represent the drop surface as a two-dimensional homogeneous fluid using the Bousinessq–Scriven law and employ Lamb's general solution to represent the velocity fields inside and outside the droplet. We obtain an expression for the cross-stream migration velocity of the droplet, where the surface viscosities are captured by the Bousinessq numbers for surface shear and surface dilatation. We elucidate the influence of the surface viscosities on the migration characteristics of the droplet and the surfactant redistribution on the droplet surface. Our study sheds light on the importance of including the droplet surface viscosities to accurately predict the migration characteristics of the droplet. 
    more » « less
  2. ; (, Soft Matter)
    Chemical concentration fields and flow patterns inside and outside of a spherical active droplet powered by collective chemotaxis. 
    more » « less
  3. ; ; (, Journal of Fluid Mechanics)
    The dynamics of an evaporating droplet in an unsteady flow is of practical interest in many industrial applications and natural processes. To investigate the transport and evaporation dynamics of such droplets, we present a numerical study of an isolated droplet in an oscillating gas-phase flow. The study uses a one-way coupled two-phase flow model to assess the effect of the amplitude and the frequency of a sinusoidal external flow field on the lifetime of a multicomponent droplet containing a non-volatile solute dissolved in a volatile solvent. The results show that the evaporation process becomes faster with an increase in the amplitude or the frequency of the gas-phase oscillation. The liquid-phase transport inside the droplet also is influenced by the unsteadiness of the external gas-phase flow. A scaling analysis based on the response of the droplet under the oscillating drag force is subsequently carried out to unify the observed evaporation dynamics in the simulations under various conditions. The analysis quantifies the enhancement in the droplet velocity and Reynolds number as a function of the gas-phase oscillation parameters and predicts the effects on the evaporation rate. 
    more » « less
  4. ; (, Journal of Fluid Mechanics)
    The encapsulation of active particles, such as bacteria or active colloids, inside a droplet gives rise to a non-trivial shape dynamics and droplet displacement. To understand this behaviour, we derive an asymptotic solution for the fluid flow about a deformable droplet containing an active particle, modelled as a Stokes-flow singularity, in the case of small shape distortions. We develop a general solution for any Stokes singularity and apply it to compute the flows and resulting droplet velocity due to common singularity representations of active particles, such as Stokeslets, rotlets and stresslets. The results show that offsetting of the active particle from the centre of the drop breaks symmetry and excites a large number of generally non-axisymmetric shape modes as well as particle and droplet motion. In the case of a swimming stresslet singularity, a run-and-tumble locomotion results in superdiffusive droplet displacement. The effect of interfacial properties is also investigated. Surfactants adsorbed at the droplet interface counteract the internal flow and arrest the droplet motion for all Stokes singularities except the Stokeslet. Our results highlight strategies to steer the flows of active particles and create autonomously navigating containers. 
    more » « less
  5. ; (, Journal of Engineering Mathematics)
    Abstract We develop a mathematical model of heat and mass transfer in a configuration which involves a spherical droplet levitating near a flat liquid layer heated from below. Analytical solutions for vapor concentration in air and the temperature distributions both inside the droplet and in moist air around it are coupled to the numerical solution for heat transfer in the liquid layer. In the limit of weak evaporation, the liquid layer surface is cooled locally due to the presence of the droplet, while the effect is reversed for strong evaporation. The latter case is also characterized by higher temperature near the bottom of the droplet and stronger temperature gradients in the droplet itself, an unexpected conclusion given the high liquid-to-air thermal conductivity ratio. The observations are explained in terms of interplay between geometric and thermal effects of the presence of the droplet. A simple analytical criterion is formulated to determine the condition when the droplet presence has no effect on the layer temperature; remarkably, the condition does not depend on the distance between the droplet and the layer surface. The calculation of the evaporation rate leads to determination of the flow around the droplet, treated in the Stokes flow approximation, as well as the levitation height. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email