2,025 research outputs found
Why surface nanobubbles live for hours
We present a theoretical model for the experimentally found but
counter-intuitive exceptionally long lifetime of surface nanobubbles. We can
explain why, under normal experimental conditions, surface nanobubbles are
stable for many hours or even up to days rather than the expected microseconds.
The limited gas diffusion through the water in the far field, the cooperative
effect of nanobubble clusters, and the pinned contact line of the nanobubbles
lead to the slow dissolution rate.Comment: 5 pages, 3 figure
Capillarity of soft amorphous solids: a microscopic model for surface stress
The elastic deformation of a soft solid induced by capillary forces crucially
relies on the excess stress inside the solid-liquid interface. While for a
liquid-liquid interface this "surface stress" is strictly identical to the
"surface free energy", the thermodynamic Shuttleworth equation implies that
this is no longer the case when one of the phases is elastic. Here we develop a
microscopic model that incorporates enthalpic interactions and entropic
elasticity, based on which we explicitly compute the surface stress and surface
free energy. It is found that the compressibility of the interfacial region,
through the Poisson ratio near the interface, determines the difference between
surface stress and surface energy. We highlight the consequence of this finding
by comparing with recent experiments and simulations on partially wetted soft
substrates
Emergent hyperuniformity in periodically-driven emulsions
We report the emergence of large-scale hyperuniformity in microfluidic
emulsions. Upon periodic driving confined emulsions undergo a first-order
transition from a reversible to an irreversible dynamics. We evidence that this
dynamical transition is accompanied by structural changes at all scales
yielding macroscopic yet finite hyperuniform structures. Numerical simulations
are performed to single out the very ingredients responsible for the
suppression of density fluctuations. We show that as opposed to equilibrium
systems the long-range nature of the hydrodynamic interactions are not required
for the formation of hyperuniform patterns, thereby suggesting a robust
relation between reversibility and hyperuniformity which should hold in a broad
class of periodically driven materials.Comment: 5p, 3f, submitte
Initial spreading of low-viscosity drops on partially wetting surfaces
Liquid drops start spreading directly after brought into contact with a
partial wetting substrate. Although this phenomenon involves a three-phase
contact line, the spreading motion is very fast. We study the initial spreading
dynamics of low-viscosity drops, using two complementary methods: Molecular
Dynamics simulations and high-speed imaging. We access previously unexplored
length- and time-scales, and provide a detailed picture on how the initial
contact between the liquid drop and the solid is established. Both methods
unambiguously point towards a spreading regime that is independent of
wettability, with the contact radius growing as the square root of time
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