18 research outputs found
Activated drying in hydrophobic nanopores and the line tension of water
International audienceWe study the slow dynamics of water evaporation out of hydro-phobic cavities by using model porous silica materials grafted with octylsilanes. The cylindrical pores are monodisperse, with a radius in the range of 1–2 nm. Liquid water penetrates in the nanopores at high pressure and empties the pores when the pressure is lowered. The drying pressure exhibits a logarithmic growth as a function of the driving rate over more than three decades, showing the ther-mally activated nucleation of vapor bubbles. We find that the slow dynamics and the critical volume of the vapor nucleus are quantita-tively described by the classical theory of capillarity without adjust-able parameter. However, classical capillarity utterly overestimates the critical bubble energy. We discuss the possible influence of surface heterogeneities, long-range interactions, and high-curvature effects, and we show that a classical theory can describe vapor nucleation provided that a negative line tension is taken into account. The drying pressure then provides a determination of this line tension with much higher precision than currently available methods. We find consistent values of the order of −30 pN in a variety of hydrophobic materials. drying transition | hydrophobicity | kinetics | nanobubbles
Thermally Activated Dynamics of the Capillary Condensation
This paper is devoted to the thermally activated dynamics of the capillary
condensation. We present a simple model which enables us to identify the
critical nucleus involved in the transition mechanism. This simple model is
then applied to calculate the nucleation barrier from which we can obtain
informations on the nucleation time. We present a simple estimation of the
nucleation barrier in slab geometry both in the two dimensional case and in the
three dimensional case. We extend the model in the case of rough surfaces which
is closer to the experimental case and allows comparison with experimental
datas.Comment: 6 pages, 3 figures, Submitted to J. Phys. : Condens. Matter,
Proceedings of the IV Liquid Matter Conference - Grenada(Spain) july 199
Aging in humid granular media
Aging behavior is an important effect in the friction properties of solid
surfaces. In this paper we investigate the temporal evolution of the static
properties of a granular medium by studying the aging over time of the maximum
stability angle of submillimetric glass beads. We report the effect of several
parameters on these aging properties, such as the wear on the beads, the stress
during the resting period, and the humidity content of the atmosphere. Aging
effects in an ethanol atmosphere are also studied. These experimental results
are discussed at the end of the paper.Comment: 7 pages, 9 figure
Water in hydrophobic micropores : dynamical behavior
International audienc
Dynamical response of water confined in hydrophobic nanometric sized porous matrices
International audienc
Flow rate in individual nanopores: a direct sensor with picoliter per minute sensitivity
International audienc
Indenter du verre avec un liquide ?
Pour décrire les écoulements à des échelles nanométriques, on postule souvent que les
fluides conservent leur comportement macroscopique à ces échelles et peuvent être décrits
par des approches de type « milieu continu ». La question suivante se pose alors
naturellement : jusqu’à quelle taille de confinement cette hypothèse reste-t-elle valable?
Dans cet article, nous montrons qu’en réalité des liquides newtoniens conservent leurs
propriétés mécaniques ordinaires à ces échelles, et que l’élasticité mesurée est en fait
celle des parois qui confinent. Il faudra en tenir compte à l’avenir. Cela ouvre une piste
nouvelle : utiliser un liquide pour sonder une paroi solide
A sensor to measure flow rate in individual nanopore
International audienc