About
50
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Introduction
I'm interested in pattern formation and collective phenomena in systems away from thermodynamic equilibrium. I combine experiments and modeling using methods of statistical physics to get a better understanding of these phenomena. Currently focused on thin films, drops, bubbles, and immiscible flows in porous media. In the past, I've studied swimming bacteria, as well as fluid flows in nano-scale confinement.
Current institution
Education
September 2012 - August 2018
September 2008 - August 2010
September 2003 - May 2008
Publications
Publications (50)
Bacteria are one of the oldest life forms on Earth, dating back to more than 3.5 billion years ago. They control the global cycling of carbon, nitrogen, and oxygen. They provide plants, fungi and other organisms with the necessary nutrients and elements. They help us digest our food, protect us against pathogens, and even affect our behavior. Micro...
Understanding how colloids move in crowded environments is key for gaining control over their transport in applications such as drug delivery, filtration, contaminant/microplastic remediation and agriculture. The classical models of colloid transport in porous media rely on geometric characteristics of the medium, and hydrodynamic/non-hydrodynamic...
Fluid instabilities can be harnessed for facile self-assembly of patterned structures on the nano- and microscale. Evaporative self-assembly from drops is one simple technique that enables a range of patterning behaviors due to the multitude of fluid instabilities that arise due to the simultaneous existence of temperature and solutal gradients. Ho...
Solute gradients next to an interface drive a diffusioosmotic flow, the origin of which lies in the intermolecular interactions between the solute and the interface. These flows on the surface of colloids introduce an effective slip velocity, driving their diffusiophoretic migration. In confined environments, we expect the interplay between diffusi...
We investigate interfacial instability in a lifting Hele-Shaw cell by experiments and theory. We characterize the unexplored transition from stable to unstable patterns under a wide range of controlling parameters. Surprisingly, we find that the perturbation growth rate-based criterion for the onset of instability from linear stability theory is to...
Water drops floating at an interface can be self-assembled and controlled using electrostatic effects. Uncharged drops can be moved around as desired, while charged drops exhibit spontaneous directed motion.
During mesenchymal migration, F-actin protrusion at the leading edge and actomyosin contraction determine the retrograde flow of F-actin within the lamella. The coupling of this flow to integrin-based adhesions determines the force transmitted to the extracellular matrix and the net motion of the cell. In tissues, motion may also arise from convect...
We present a theoretical study of viscous slug motion inside a microscopically rough capillary tube, where pronounced stick–slip motion can emerge at slow displacement rates. The mathematical description of this intermittent motion can be reduced to a system of ordinary differential equations, which also describe the motion of a pendulum inside a f...
Droplets of alcohol-based formulations are common in applications from sanitizing sprays to printing inks. However, our understanding of the drying dynamics of these droplets on surfaces and the influence of ambient humidity is still very limited. Here, we report the drying dynamics of picoliter droplets of isopropyl alcohol deposited on a surface...
The wetting behaviour of drops on rigid and elastic fibres is important in many applications including textiles, fog collection, systems with absorbent fibres, and in natural settings such as spiderwebs. Yet, little is known about the behaviour of fibre-attached drops when exposed to a background air flow. Additionally, control of drop motion and c...
Immiscible fluid-fluid displacement in confined geometries is a fundamental process occurring in many natural phenomena and technological applications, from geological CO2 sequestration to microfluidics. Due to the interactions between the fluids and the solid walls, fluid invasion undergoes a wetting transition from complete displacement at low di...
For almost 200 y, the dominant approach to understand oil-on-water droplet shape and stability has been the thermodynamic expectation of minimized energy, yet parallel literature shows the prominence of Marangoni flow, an adaptive gradient of interfacial tension that produces convection rolls in the water. Our experiments, scaling arguments, and li...
We study numerically the effect of a soluble surfactant on the stability of two-phase flow in a finite-length microchannel. We calculate the steady base flow and its global eigenmodes for experimentally relevant choices of material, kinetic, and flow parameters. The results show that the system is unstable for capillary numbers above a critical val...
Coalescence and breakup of drops are classic problems in fluid physics that often involve self-similarity and singularity formation. While the coalescence of suspended drops is axisymmetric, the coalescence of drops on a substrate is inherently three-dimensional. Yet, studies so far have only considered this problem in two dimensions. In this Lette...
We study numerically the effect of a soluble surfactant on the stability of two-phase flow in a finite-length microchannel. We calculate the steady base flow and its global eigenmodes for experimentally relevant choices of material, kinetic, and flow parameters. The results show that the surfactant surface concentration takes values of the order of...
Parallel two-phase flows are omnipresent in technological applications that require contact between two immiscible fluids for a finite amount of time. Precise control over the flow and separation of the fluids once they have been in contact are therefore the key challenges in these applications. Here, using experiments and numerical simulations, we...
Fluid–fluid displacement in porous media has been viewed through the lens of Lenormand's phase diagram since the late 1980s. This diagram suggests that the character of the flow is controlled by two dimensionless parameters: the capillary number and the viscosity ratio. It is by now well known, however, that the wettability of the system plays a ke...
Small multicomponent droplets are of increasing importance in a plethora of technological applications ranging from the fabrication of self-assembled hierarchical patterns to the design of autonomous fluidic systems. While often far away from equilibrium, involving complex and even chaotic flow fields, it is commonly assumed that in these systems w...
Natural soils are host to a high density¹ and diversity² of microorganisms, and even deep-earth porous rocks provide a habitat for active microbial communities³. In these environments, microbial transport by disordered flows is relevant for a broad range of natural and engineered processes, from biochemical cycling to remineralization and bioremedi...
It is now recognized that aerosol transport contributes to the transmission of the SARS-CoV-2 virus. Here, we improve existing social distancing guidelines for airborne pathogens, which are typically given in terms of distance with vague statements about contact times. Also, estimates of inhalation of virus in a contaminated space usually assume a...
Imbibition in a porous medium plays a central role in diverse energy, environmental, and industrial processes. In many cases, the medium has multiple parallel strata of different permeabilities; however, how this stratification impacts imbibition is poorly understood. We address this gap in knowledge by directly visualizing forced imbibition in thr...
When one fluid displaces another in a confined environment, some energy is dissipated in the fluid bulk and the rest is dissipated near the contact line. Here we study the relative strengths of these two sources of dissipation with a novel experimental setup: constant-rate spontaneous imbibition experiments, achieved by introducing a viscous oil sl...
Imbibition plays a central role in diverse energy, environmental, and industrial processes. In many cases, the medium has multiple parallel strata of different permeabilities; however, how this stratification impacts imbibition is poorly understood. We address this gap in knowledge by directly visualizing forced imbibition in three-dimensional (3D)...
It is now recognized that aerosol transport contributes to the transmission of the SARS-CoV-2. Existing social distancing guidelines are given in terms of distance, with vague statements about contact times. Also, estimates of inhalation of virus in a contaminated space typically assume a well-mixed environment, which is realistic for some, but not...
We study the hydrodynamic coupling between particles and solid, rough boundaries characterized by random surface textures. Using the Lorentz reciprocal theorem, we derive analytical expressions for the grand mobility tensor of a spherical particle and find that roughness-induced velocities vary nonmonotonically with the characteristic wavelength of...
We study the hydrodynamic coupling between particles and solid, rough boundaries characterized by random surface textures. Using the Lorentz reciprocal theorem, we derive analytical expressions for the grand mobility tensor of a spherical particle and find that roughness-induced velocities vary nonmonotonically with the characteristic wavelength of...
We present the results of a combined experimental and theoretical study of the spin coating of the inner surface of capillary tubes with viscous liquids, and the modified Rayleigh-Plateau instability that arises when the spinning stops. We show that during the spin coating, the thinning of the film is governed by the balance of viscous and centrifu...
We develop a novel ‘moving-capacitor’ dynamic network model to simulate immiscible fluid–fluid displacement in porous media. Traditional network models approximate the pore geometry as a network of fixed resistors, directly analogous to an electrical circuit. Our model additionally captures the motion of individual fluid–fluid interfaces through th...
Significance
We observe the formation of bubbles and drops on a daily basis, from dripping faucets to raindrops entraining bubbles on the surface of a lake. The ubiquity of the phenomenon masks the fascinating underlying nonlinear dynamics that is such an important aspect of modern physics. Here, we report on the surprising observation that confine...
We develop a novel `moving capacitor' dynamic network model to simulate immiscible fluid-fluid displacement in porous media. Traditional network models approximate the pore geometry as a network of fixed resistors, directly analogous to an electrical circuit. Our model additionally captures the motion of individual fluid-fluid interfaces through th...
A uniform nanometric thin liquid film on a solid substrate can become unstable due to the action of van der Waals (vdW) forces. The instability leads to dewetting of the uniform film and the formation of drops. To minimize the total free energy of the system, these drops coarsen over time until one single drop remains. Here, using a thermodynamical...
Immiscible fluid-fluid displacement in partial wetting continues to challenge our microscopic and macroscopic descriptions. Here, we study the displacement of a viscous fluid by a less viscous fluid in a circular capillary tube in the partial wetting regime. In contrast with the classic results for complete wetting, we show that the presence of a m...
Immiscible fluid flows are ubiquitous in nature and industry, from multiphase-flow phenomena on geologic scales such as CO2 sequestration and methane venting from seafloor sediments to bubble/drop/emulsion generation in microfluidic techniques. All these flows are inherently multi-scale, from the intermolecular interactions on the nanometer scale i...
When a liquid touches a solid surface, it spreads to minimize the system's energy. The classic thin-film model describes the spreading as an interplay between gravity, capillarity, and viscous forces, but it cannot see an end to this process as it does not account for the nonhydrodynamic liquid-solid interactions. While these interactions are impor...
A kinetic model and three-dimensional numerical simulations are applied to study the dynamics in suspensions of run-and-tumble aerotactic bacteria confined in free-standing liquid films surrounded by air. In thin films, oxygen and bacterial concentration profiles approach steady states. In thicker films, a transition to chaotic dynamics is shown to...
This fluid dynamics video presents three-dimensional kinetic simulations of
the dynamics in suspensions of oxytactic bacteria confined in thin liquid film
surrounded by air. At the initial time, the bacterial concentration is uniform
and isotropic, and there is no oxygen inside the film. The spatio-temporal
dynamics of the oxygen and bacterial conc...
The dependence of velocity slip at a liquid-solid interface upon the character of the solid is studied using atomistic simulation methods for Lennard-Jones model systems. The effect of the thermostatting mechanisms, often used in such simulations, is also investigated. The solid atom vibrational frequency is shown not to have a significant effect o...
The effects of an external shear flow on the dynamics and pattern formation in a dilute suspension of swimming micro-organisms are investigated using a linear stability analysis and three-dimensional numerical simulations, based on the kinetic model previously developed by [D. Saintillan and M. J. Shelley, Phys. Fluids 20, 123304 (2008)]. The exter...
We investigate the dynamics in suspensions of aerotactic bacteria using two different kinetic models: a gradient-detecting model, in which the bacteria detect the local oxygen gradients instantaneously, and a run-and-tumble model, in which the bacteria change their run-and-tumble frequency based on the recent temporal changes in the oxygen field. U...
Suspensions of self-propelled particles, such as swimming micro-organisms, are known to undergo complex dynamics as a result of hydrodynamic interactions. Using the kinetic theory recently developed by Saintillan and Shelley (``Instabilities, pattern formation, and mixing in active suspensions'', Physics of Fluids 20, 123304, 2008), we investigate...
Suspensions of self-propelled particles, such as swimming micro-organisms, are known to undergo complex dynamics as a result of hydrodynamic interactions. This fluid dynamics video presents a numerical simulation of such a suspension, based on a kinetic theory recently developed by Saintillan and Shelley (Physics of Fluids, 20, 123403, 2008). Start...
In the present work, unsteady MHD flow of a Maxwellian fluid above an impulsively stretched sheet is studied under the assumption that boundary layer approximation is applicable. The objective is to find an analytical solution which can be used to check the performance of computational codes in cases where such an analytical solution does not exist...
Flow induced in a viscoelastic fluid by a linearly stretched sheet is investigated assuming that the fluid is Maxwellian and the sheet is subjected to a transverse magnetic field. The objective is to investigate the effects of parameters such as elasticity number, magnetic number, radiative heat transfer, Prandtl number, and Eckert number on the te...
The performance of a two-auxiliary-parameter homotopy analysis method (HAM) is investigated in solving laminar MHD flow of an upper-convected Maxwell fluid (UCM) above a porous isothermal stretching sheet. The analysis is carried out up to the 20th-order of approximation, and the effect of parameters such as elasticity number, suction/injection vel...
In this Letter, we propose a simple approach using HAM to obtain accurate totally analytical solution of viscous fluid flow over a flat plate. First, we show that the solution obtained using HPM is not a reliable one; moreover, we show that HPM is only a special case of HAM and its basic assumptions are restrictive rather than useful. We set ℏ=−1 f...
Micro-organisms first appeared on earth about 3.8 billion years ago and can be found almost everywhere now. In terms of number and biomass, they in fact constitute the majority of terrestrial life and despite their tiny size play a vital role in a wide variety of phenomena. Although there has been a long history of studying characteristics of indiv...
