79 research outputs found
Dynamics of surfactant-laden evaporating droplets
We consider the flow dynamics of a thin evaporating droplet in\ud
the presence of an insoluble surfactant and small particles in the bulk. Evolution\ud
equations for the film height, the interfacial surfactant and bulk particle concentra-\ud
tion are derived using a lubrication model coupled by a constitutive relation for the\ud
dependence of the viscosity on local particle concentration. An important ingredient\ud
of our model is that it takes into account the fact that the surfactant adsorbed at\ud
the surface hinders the evaporation. Time-dependent simulations are performed to\ud
determine how the presence of surfactants affects the evaporation and flow dynamics\ud
with and without the presence of particles in the bulk. We discuss the various mech-\ud
anisms that affect the shape of the droplet as it evaporates as well as the resulting\ud
pattern of particle deposition
The stability of slowly evaporating thin liquid films of binary mixtures
We consider the evaporation of a thin liquid layer which consists of a binary
mixture of volatile liquids. The mixture is on top of a heated substrate and in
contact with the gas phase that consists of the same vapour as the binary
mixture. The effect of thermocapillarity, solutocapillarity and the van der
Waals interactions are considered. We derive the long-wave evolution equations
for the free interface and the volume fraction that govern the two-dimensional
stability of the layer subject to the above coupled mechanisms and perform a
linear stability analysis. Our results demonstrate two modes of instabilities,
a monotonic instability mode and an oscillatory instability mode. We supplement
our results from stability analysis with transient simulations to examine the
dynamics in the nonlinear regime and analyse how these instabilities evolve
with time. More precisely we discuss how the effect of relative volatility
along with the competition between thermal and solutal Marangoni effect defines
the mode of instability that develops during the evaporation of the liquid
layer due to preferential evaporation of one of the components.Comment: 19 page
Spreading and retraction dynamics of sessile evaporating droplets comprising volatile binary mixtures
Abstract </jats:p
Physics-agnostic and Physics-infused machine learning for thin films flows: modeling, and predictions from small data
Numerical simulations of multiphase flows are crucial in numerous engineering
applications, but are often limited by the computationally demanding solution
of the Navier-Stokes (NS) equations. Here, we present a data-driven workflow
where a handful of detailed NS simulation data are leveraged into a
reduced-order model for a prototypical vertically falling liquid film. We
develop a physics-agnostic model for the film thickness, achieving a far better
agreement with the NS solutions than the asymptotic Kuramoto-Sivashinsky (KS)
equation. We also develop two variants of physics-infused models providing a
form of calibration of a low-fidelity model (i.e. the KS) against a few
high-fidelity NS data. Finally, predictive models for missing data are
developed, for either the amplitude, or the full-field velocity and even the
flow parameter from partial information. This is achieved with the so-called
"Gappy Diffusion Maps", which we compare favorably to its linear counterpart,
Gappy POD
Linear and nonlinear stability of hydrothermal waves in planar liquid layers driven by thermocapillarity
A shallow planar layer of liquid bounded from above by gas is set into motion via the thermocapillary effect resulting from a thermal gradient applied along its interface. Depending on the physical properties of the liquid and the strength of the gradient, the system is prone to departure from its equilibrium state and to the consequent development of an oscillatory regime. This problem is numerically investigated for the first time by means of two-phase direct numerical simulations fully taking into account the presence of a deformable interface. Obliquely travelling hydrothermal waves (HTWs), similar to those first described by Smith and Davis [J. Fluid Mech. 132, 119-144 (1983)], are reported presenting good agreement with linear stability theory and experiments. The nonlinear spatiotemporal growth of the instabilities is discussed extensively along with the final bulk flow for both the liquid and gas phases. Our study reveals the presence of interface deformations which accompany the HTWs pattern with a certain time-delay. The local interface heat fluxes are found to be significantly affected by the transient nature of the HTWs, contradicting the results of previous single-phase studies. (C) 2013 AIP Publishing LLC
Non-isothermal bubble rise:Non-monotonic dependence of surface tension on temperature
We study the motion of a bubble driven by buoyancy and thermocapillarity in a tube with a non-uniformly heated walls, containing a so-called ‘self-rewetting fluid’; the surface tension of the latter exhibits a parabolic dependence on temperature, with a well-defined minimum. In the Stokes flow limit, we derive the conditions under which a spherical bubble can come to rest in a self-rewetting fluid whose temperature varies linearly in the vertical direction, and demonstrate that this is possible for both positive and negative temperature gradients. This is in contrast to the case of simple fluids whose surface tension decreases linearly with temperature, for which bubble motion is arrested only for negative temperature gradients. In the case of self-rewetting fluids, we propose an analytical expression for the position of bubble arrestment as a function of other dimensionless numbers. We also perform direct numerical simulation of axisymmetric bubble motion in a fluid whose temperature increases linearly with vertical distance from the bottom of the tube; this is done for a range of Bond and Galileo numbers, as well as for various parameters that govern the functional dependence of surface tension on temperature. We demonstrate that bubble motion can be reversed and then arrested only in self-rewetting fluids, and not in linear fluids, for sufficiently small Bond numbers. We also demonstrate that considerable bubble elongation is possible under significant wall confinement, and for strongly self-rewetting fluids and large Bond numbers. The mechanisms underlying the phenomena observed are elucidated by considering how the surface tension dependence on temperature affects the thermocapillary stresses in the flow
Development of BromoTag:A “Bump-&-Hole”-PROTAC system to induce potent, rapid, and selective degradation of tagged target proteins
[Image: see text] Small-molecule-induced protein depletion technologies, also called inducible degrons, allow degradation of genetically engineered target proteins within cells and animals. Here, we design and develop the BromoTag, a new inducible degron system comprising a Brd4 bromodomain L387A variant as a degron tag that allows direct recruitment by heterobifunctional bumped proteolysis targeting chimeras (PROTACs) to hijack the VHL E3 ligase. We describe extensive optimization and structure–activity relationships of our bump-and-hole–PROTACs using a CRISPR knock-in cell line expressing model target BromoTag-Brd2 at endogenous levels. Collectively, our cellular and mechanistic data qualifies bumped PROTAC AGB1 as a potent, fast, and selective degrader of BromoTagged proteins, with a favorable pharmacokinetic profile in mice. The BromoTag adds to the arsenal of chemical genetic degradation tools allowing us to manipulate protein levels to interrogate the biological function and therapeutic potential in cells and in vivo
Rapidly prototyping biocompatible surfaces with designed wetting properties via photolithography and plasma polymerization
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