122 research outputs found
Softening of edges of solids by surface tension
Surface tension tends to minimize the area of interfaces between pieces of
matter in different thermodynamic phases, be they in the solid or the liquid
state. This can be relevant for the macroscopic shape of very soft solids, and
lead to a roughening of initially sharp edges. We calculate this effect for a
neo-Hookean elastic solid, with assumptions corresponding to actual
experiments, namely the case where an initially sharp edge is rounded by the
effect of surface tension felt when the fluid surrounding the soft solid (and
so surface tension) is changed at the solid/liquid boundary. We consider two
opposite limits where the analysis can be carried to the end, the one of a
shallow angle and the one of a very sharp angle. Both cases yield a
discontinuity of curvature in the state with surface tension although the
initial state had a discontinuous slope
Take-off of small Leidenfrost droplets
We put in evidence the unexpected behaviour of Leidenfrost droplets at the
later stage of their evaporation. We predict and observe that, below a critical
size , the droplets spontaneously take-off due to the breakdown of the
lubrication regime. We establish the theoretical relation between the droplet
radius and its elevation. We predict that the vapour layer thickness increases
when the droplets become smaller. A satisfactory agreement is found between the
model and the experimental results performed on droplets of water and of
ethanol.Comment: Accepted for publication in Phys. Rev. Lett. (2012
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