Biomedical subjects

F Caillier

Publications and source records attributed to F Caillier.

3 recordsLinked to original sources

PubMed2006

Collapse dynamics of smectic-A bubbles.

The collapse dynamics of smectic-A bubbles are analyzed experimentally and theoretically. Each bubble is expanded from a flat film stretched at the end of a hollow cylinder and deflated through a pressure release by means of a capillary tube. Its total collapse time can be varied between 0.1s and 20s by suitably choosing the length and the internal diameter of the capillary. This experiment allowed us to show that the collapse takes place in two steps: an initial one, which lasts a fraction of a second, where the meniscus destabilizes and fills up with focal conics, followed by a much longer period during which the bubble collapses and exchanges material with the meniscus. By measuring simultaneously the Laplace pressure and the internal pressure inside the bubble, we were able to fully characterize the shear-thinning behavior of the smectic phase within the meniscus. We emphasize that this method is generic and could be applied as well to other systems such as soap bubbles, on condition that inertial effects are negligible.

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PubMed2004

Direct measurement of the permeability of the meniscus bordering a free-standing smectic-A film.

A smectic-A free-standing film is always connected by a meniscus to the frame on which it has been stretched. The meniscus acts as a dissipative reservoir and is characterized by its permeability. We propose a method to measure directly this quantity by equilibrating two menisci in correspondence with the same free-standing film. The permeability is shown to depend on the film thickness, in full agreement with previous indirect measurements obtained by analyzing the growth dynamics of dislocation loops. An improved model of the meniscus is proposed to interpret all the data.

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PubMed2003

Dislocation loop dynamics in freestanding smectic films: the role of the disjoining pressure and of the finite permeability of the meniscus.

When a dislocation loop nucleates in a freestanding film, it collapses or grows depending on whether its radius r is smaller or larger than a critical radius r(c). In this paper, we analyze the growth dynamics of a dislocation loop in the limit of r>>r(c). Experiments with pure octylcyanobiphenyl show that the dislocation velocity is constant in thick films (more than 100 layers) regardless of their thicknesses, and only depends on the pressure in the meniscus. At intermediate thickness (between 100 and 15 layers), the velocity is no longer constant and tends to decrease in time on account of the finite permeability of the meniscus. In very thin films (less than 15 layers), the dislocations move faster than in thick films, although their velocities continue to decrease in time. The thinner the film, the larger the global acceleration is. This effect is linked to a supplementary force acting on the dislocations caused by the attraction between the free surfaces (where the smectic order parameter is enhanced). The progressive deceleration is due to the finite permeability of the meniscus.

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