70 research outputs found
Capillary Condensation in Confined Media
We review here the physics of capillary condensation of liquids in confined
media, with a special regard to the application in nanotechnologies. The
thermodynamics of capillary condensation and thin film adsorption are first
exposed along with all the relevant notions. The focus is then shifted to the
modelling of capillary forces, to their measurements techniques (including SFA,
AFM and crack tips) and to their influence on AFM imaging techniques as well as
on the static and dynamic friction properties of solids (including granular
heaps and sliding nanocontacts). A great attention is spent in investigating
the delicate role of the surface roughness and all the difficulties involved in
the reduction of the probe size to nanometric dimensions. Another major
consequence of capillary condensation in nanosystems is the activation of
several chemical and corrosive processes that can significantly alter the
surface properties, such as dissolution/redeposition of solid materials and
stress-corrosion crack propagation.Comment: 28 pages - To appear in 2010 in the Handbook of Nanophysics - Vol 1 -
Edited by Klaus Sattler - CRC Pres
Giant osmotic pressure in the forced wetting of hydrophobic nanopores
The forced intrusion of water in hydrophobic nanoporous pulverulent material
is of interest for quick storage of energy. With nanometric pores the energy
storage capacity is controlled by interfacial phenomena. With subnanometric
pores, we demonstrate that a breakdown occurs with the emergence of molecular
exclusion as a leading contribution. This bulk exclusion effect leads to an
osmotic contribution to the pressure that can reach levels never previously
sustained. We illustrate on various electrolytes and different microporous
materials, that a simple osmotic pressure law accounts quantitatively for the
enhancement of the intrusion and extrusion pressures governing the forced
wetting and spontaneous drying of the nanopores. Using electrolyte solutions,
energy storage and power capacities can be widely enhanced
Proximity effect on hydrodynamic interaction between a sphere and a plane measured by Force Feedback Microscopy at different frequencies
In this article, we measure the viscous damping and the associated
stiffness of a liquid flow in sphere-plane geometry in a large frequency
range. In this regime, the lubrication approximation is expected to dominate.
We first measure the static force applied to the tip. This is made possible
thanks to a force feedback method. Adding a sub-nanometer oscillation of the
tip, we obtain the dynamic part of the interaction with solely the knowledge of
the lever properties in the experimental context using a linear transformation
of the amplitude and phase change. Using a Force Feedback Microscope (FFM)we
are then able to measure simultaneously the static force, the stiffness and the
dissipative part of the interaction in a broad frequency range using a single
AFM probe. Similar measurements have been performed by the Surface Force
Apparatus with a probe radius hundred times bigger. In this context the FFM can
be called nano-SFA
Out of equilibrium anomalous elastic response of a water nano-meniscus
We report the observation of a transition in the dynamical properties of
water nano-menicus which dramatically change when probed at different time
scales. Using a AFM mode that we name Force Feedback Microscopy, we observe
this change in the simultaneous measurements, at different frequencies, of the
stiffness G'(N/m), the dissipative coefficient G''(kg/sec) together with the
static force. At low frequency we observe a negative stiffness as expected for
capillary forces. As the measuring time approaches the microsecond, the dynamic
response exhibits a transition toward a very large positive stiffness. When
evaporation and condensation gradually lose efficiency, the contact line
progressively becomes immobile. This transition is essentially controlled by
variations of Laplace pressure
Intrusion and extrusion of water in hydrophobic mesopores
We present experimental and theoretical results on intrusion-extrusion cycles
of water in hydrophobic mesoporous materials, characterized by independent
cylindrical pores. The intrusion, which takes place above the bulk saturation
pressure, can be well described using a macroscopic capillary model. Once the
material is saturated with water, extrusion takes place upon reduction of the
externally applied pressure; Our results for the extrusion pressure can only be
understood by assuming that the limiting extrusion mechanism is the nucleation
of a vapour bubble inside the pores. A comparison of calculated and
experimental nucleation pressures shows that a proper inclusion of line tension
effects is necessary to account for the observed values of nucleation barriers.
Negative line tensions of order are found for our
system, in reasonable agreement with other experimental estimates of this
quantity
Nanorhéomètre pour l’étude des liquides confiné
International audienceNanorhéomètre pour la mesure des propriétés mécaniques sans contac
Effect of Surface Elasticity on the Rheology of Nanometric Liquids
International audienceThe rheological properties of liquids con ned to nanometer scales are important in many physical situations. In this paper we demonstrate that the long range elastic deformation of the con ning surfaces must be taken into account when considering the rheology of nanometric liquids. In the case of a squeeze- ow geometry, we show that below a critical distance Dc the liquid is clamped by its viscosity and its intrinsic properties cannot be disentangled from the global system response. Using nanorheology experiments, we demonstrate that picometer elastic de ections of the rigid con ning surfaces dominate the overall mechanical response of nanometric liquids con ned between solid walls
Low Friction Flows of Liquids at Nanopatterned Interfaces
With the recent important development of microfluidic systems,
miniaturization of flow devices has become a real challenge. Microchannels,
however, are characterized by a large surface to volume ratio, so that surface
properties strongly affect flow resistance in submicrometric devices. We
present here results showing that the concerted effect of wetting . properties
and surface roughness may considerably reduce friction of the fluid past the
boundaries. The slippage of the fluid at the channel boundaries is shown to be
drastically increased by using surfaces that are patterned at the nanometer
scale. This effect occurs in the regime where the surface pattern is partially
dewetted, in the spirit of the 'superhydrophobic' effects that have been
recently discovered at the macroscopic scales. Our results show for the first
time that, in contrast to the common belief, surface friction may be reduced by
surface roughness. They also open the possibility of a controlled realization
of the 'nanobubbles' that have long been suspected to play a role in
interfacial slippag
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