32 research outputs found
Drop impact on a flexible fiber
When droplets impact fibrous media, the liquid can be captured by the fibers
or contact then break away. Previous studies have shown that the efficiency of
drop capture by a rigid fiber depends on the impact velocity and defined a
threshold velocity below which the drop is captured. However, it is necessary
to consider the coupling of elastic and capillary effects to achieve a greater
understanding of the capture process for soft substrates. Here, we study
experimentally the dynamics of a single drop impacting on a thin flexible
fiber. Our results demonstrate that the threshold capture velocity depends on
the flexibility of fibers in a non-monotonic way. We conclude that tuning the
mechanical properties of fibers can optimize the efficiency of droplet capture.Comment: Soft Matter (2015
Damping of liquid sloshing by foams: from everyday observations to liquid transport
We perform experiments on the sloshing dynamics of liquids in a rectangular
container submitted to an impulse. We show that when foam is placed on top of
the liquid the oscillations of the free interface are significantly damped. The
ability to reduce sloshing and associated splashing could find applications in
numerous industrial processes involving liquid transport.Comment: Accepted for publication in Journal of Visualizatio
Wetting morphologies on an array of fibers of different radii
We investigate the equilibrium morphology of a finite volume of liquid placed
on two parallel rigid fibers of different radii. As observed for identical
radii fibers, the liquid is either in a column morphology or adopts a drop
shape depending on the inter-fiber distance. However the cross-sectional area
and the critical inter-fiber distance at which the transition occurs are both
modified by the polydispersity of the fibers. Using energy considerations, we
analytically predict the critical inter-fiber distance corresponding to the
transition between the column and the drop morphologies occurs. This distance
depends both on the radii of the fibers and on the contact angle of the liquid.
We perform experiments using a perfectly wetting liquid on two parallel nylon
fibers: the results are in good agreement with our analytical model. The
morphology of the capillary bridges between fibers of different radii is
relevant to the modeling of large arrays of polydisperse fibers
Wetting morphologies on randomly oriented fibers
We characterize the different morphologies adopted by a drop of liquid placed
on two randomly oriented fibers, which is a first step toward understanding the
wetting of fibrous networks. The present work reviews previous modeling for
parallel and touching crossed fibers and extends it to an arbitrary orientation
of the fibers characterized by the tilting angle and the minimum spacing
distance. Depending on the volume of liquid, the spacing distance between
fibers and the angle between the fibers, we highlight that the liquid can adopt
three different equilibrium morphologies: (1) a column morphology in which the
liquid spreads between the fibers, (2) a mixed morphology where a drop grows at
one end of the column or (3) a single drop located at the node. We capture the
different morphologies observed using an analytical model that predicts the
equilibrium configuration of the liquid based on the geometry of the fibers and
the volume of liquid
Capillary Sorting of Particles by Dip Coating
In this letter, we describe the capillary sorting of particles by size based
on dip coating. A substrate withdrawn from a liquid bath entrains a coating
whose thickness depends on the withdrawal speed and the liquid properties. If
the coating material contains particles, they will only be entrained when the
viscous force pulling them with the substrate overcomes the opposing capillary
force at the deformable meniscus. This force threshold occurs at different
liquid thicknesses for particles of different sizes. Here, we show that this
difference can be used to separate small particles from a mixed suspension
through capillary filtration. In a bidisperse suspension, we observe three
distinct filtration regimes. At low capillary numbers, Ca, no particles are
entrained in the liquid coating. At high Ca, all particle sizes are entrained.
For a range of capillary numbers between these two extremes, only the smallest
particles are entrained while the larger ones remain in the reservoir. We
explain how this technique can be applied to polydisperse suspension. We also
provide an estimate of the range of capillary number to separate particles of
given sizes. The combination of this technique with the scalability and
robustness of dip coating makes it a promising candidate for high-throughput
separation or purification of industrial and biomedical suspensions
Clogging by sieving in microchannels: Application to the detection of contaminants in colloidal suspensions
We report on a microfluidic method that allows measurement of a small
concentration of large contaminants in suspensions of solid micrometer-scale
particles. To perform the measurement, we flow the colloidal suspension through
a series of constrictions, i.e. a microchannel of varying cross-section. We
show and quantify the role of large contaminants in the formation of clogs at a
constriction and the growth of the resulting filter cake. By measuring the time
interval between two clogging events in an array of parallel microchannels, we
are able to estimate the concentration of contaminants whose size is selected
by the geometry of the microfluidic device. This technique for characterizing
colloidal suspensions offers a versatile and rapid tool to explore the role of
contaminants on the properties of the suspensions
Mechanical tuning of the evaporation rate of liquid on crossed fibers
We investigate experimentally the drying of a small volume of perfectly
wetting liquid on two crossed fibers. We characterize the drying dynamics for
the three liquid morphologies that are encountered in this geometry: drop,
column and a mixed morphology, in which a drop and a column coexist. For each
morphology, we rationalize our findings with theoretical models that capture
the drying kinetics. We find that the evaporation rate depends significantly on
the liquid morphology and that the drying of liquid column is faster than the
evaporation of the drop and the mixed morphology for a given liquid volume.
Finally, we illustrate that shearing a network of fibers reduces the angle
between them, changes the morphology towards the column state, and so enhances
the drying rate of a volatile liquid deposited on it