Séminaire Exceptionnel
"Matière et Systèmes Complexes"


Mercredi 18 juillet juin 2007 à 11h30
Bâtiment Condorcet, 6ème étage, salle 646 A.

Howard Stone
(Harvard University) 

Manipulating thin-film flows: from patterned substrates to evaporating systems

It is well known that fluid flow in thin films occurs in a wide range of applications. Here we describe two variants of the standard kind of problem.
First, we describe the spreading of mostly wetting liquid droplets on microdecorated surfaces, i.e. assemblies of micron-size cylindrical posts arranged on square or hexagonal arrays. We obtain a variety of deterministic final shapes of the spreading droplets, including octagons, squares, hexagons and circles. Dynamic consideration provide a “shape” diagram that summarizes our observations and suggests rules for a designer’s tool box, which thus offer opportunities for control of the spreading patterns.
Second, we consider evaporation of volatile liquids on substrates with arbitrary thermal conductivity. Using experiments and theory we show how the sense of the internal circulation depends on the ratio of the liquid and substrate conductivities.
These results help rationalize previous studies of similar problems.