Abstracts - KTH Mechanics

Elastocapillarity in wet hairs
J. Bico ∗ ,C.Py ∗ ,B.Roman ∗ ,S.Neukirch † , A. Boudaoud ‡ ,C.Baroud §
The hairs of a dog coming out of a pond assemble into bunches giving it a spiny
appearance. What is the number of hairs in a clump? The answer relies on a balance
between capillary forces and elasticity of the hairs. From a practical point of view, the
sticking of flexible elements dramatically damages mechanical microsystems or lung
airways, but also allows the self-organization of the hairs of nanotube carpets into
well defined structures. Experiments performed with macroscopic brushes teach us
that the bundles results from a self-similar cascade of sticking events, which leads to
an original form of coalescence process (figure 1). Preliminary results obtained with
1D brushes of parallel strips 1 will be completed by recent experiments involving 2D
brushes of fibers. Other configurations involving self-crumpling of elastic sheets by
capillarity and the fate of a flexible strut pushed through an interface will be finally
discussed.
∗ PMMH-ESPCI, 75231 Paris, France
† LMM-UPMC, 75252 Paris, France
‡ LPS-ENS, 75230 Paris, France
§ LadHyx-École Polytechnique, 91128 Palaiseau, France
1 Bico et al, Nature 432, 690 (2004).
a
b
Figure 1: Brush of parallel strips progressively withdrawn from a liquid bath: a
cascade of sticking events leads to a hierarchical structure
c
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