9,566 research outputs found
Stability of Big Surface Bubbles: Impact of Evaporation and Bubbles Size
Surface bubbles have attracted much interest in the past decades. In this
article, we propose to explore the lifetime and thinning dynamics of
centimetric surface bubbles. We study the impact of the bubbles size as well as
that of the atmospheric humidity through a careful control and systematic
variation of the relative humidity in the measuring chamber. We first adress
the question of the drainage under saturated water vapor conditions and show
that a model including both capillary and gravity driven drainage provides the
best prediction for this process. Additionally, unprecedented statistics on the
bubbles lifetimes confirm experimentally that this parameter is set by
evaporation to leading order. We make use of a model based on the overall
thinning dynamics of the thin film and assume a rupture thickness of the order
10-100 nm to obtain a good representation of these data. For experiments
conducted far from saturation, the convective evaporation of the bath is shown
to dominate the overall mass loss in the cap film due to evaporation
Thermocapillary flows and interface deformations produced by localized laser heating in confined environment
The deformation of a fluid-fluid interface due to the thermocapillary stress
induced by a continuous Gaussian laser wave is investigated analytically. We
show that the direction of deformation of the liquid interface strongly depends
on the viscosities and the thicknesses of the involved liquid layers. We first
investigate the case of an interface separating two different liquid layers
while a second part is dedicated to a thin film squeezed by two external layers
of same liquid. These results are predictive for applications fields where
localized thermocapillary stresses are used to produce flows or to deform
interfaces in presence of confinement, such as optofluidics
Surfactant effects in the Landau–Levich problem
In this work we study the classical Landau–Levich problem of dip-coating. While in the clean interface case and in the limit of low capillary numbers it admits an asymptotic solution, its full study has not been conducted. With the help of an efficient numerical algorithm, based on a boundary-integral formulation and the appropriate set of interfacial and inflow boundary conditions, we first study the film thickness behaviour for a clean interface problem. Next, the same algorithm allows us to investigate the response of this system to the presence of soluble surface active matter, which leads to clarification of its role in the flow dynamics. The main conclusion is that pure hydrodynamical modelling of surfactant effects predicts film thinning and therefore is not sufficient to explain the film thickening observed in many experiments
Marangoni flow in freely suspended liquid films
We demonstrate controlled material transport driven by temperature gradients
in thin freely suspended smectic films. The films with submicrometer
thicknesses and lateral extensions of several millimeters were studied in
microgravity during suborbital rocket flights. In-plane temperature gradients
cause two specific Marangoni effects, directed flow and convection patterns. At
low gradients, practically thresholdless, flow transports material with a
normal (negative) temperature coefficient of the surface tension,
, from the hot to the cold film edge. That material accumulates
at the cold film border. In materials with positive temperature coefficient,
, the reverse transport from the cold to the hot edge is
observed. We present a model that describes the effect quantitatively.Comment: 5 pages, 5 figure
Diffusiophoresis in non-adsorbing polymer solutions: the Asakura-Oosawa model and stratification in drying films
A colloidal particle placed in an inhomogeneous solution of smaller
non-adsorbing polymers will move towards regions of lower polymer
concentration, in order to reduce the free energy of the interface between the
surface of the particle and the solution. This phenomenon is known as
diffusiophoresis. Treating the polymer as penetrable hard spheres, as in the
Asakura-Oosawa model, a simple analytic expression for the diffusiophoretic
drift velocity can be obtained. In the context of drying films we show that
diffusiophoresis by this mechanism can lead to stratification under easily
accessible experimental conditions. By stratification we mean spontaneous
formation of a layer of polymer on top of a layer of the colloid. Transposed to
the case of binary colloidal mixtures, this offers an explanation for the
stratification observed recently in these systems [A. Fortini et al, Phys. Rev.
Lett. 116, 118301 (2016)]. Our results emphasise the importance of treating
solvent dynamics explicitly in these problems, and caution against the neglect
of hydrodynamic interactions or the use of implicit solvent models in which the
absence of solvent backflow results in an unbalanced osmotic force which gives
rise to large but unphysical effects.Comment: 11 pages, 6 figure
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