Biomedical subjects

B Pouligny

Publications and source records attributed to B Pouligny.

11 recordsLinked to original sources

PubMed2006

Wetting and contact lines of micrometer-sized ellipsoids.

We experimentally and theoretically investigate the shapes of contact lines on the surfaces of micrometer-sized polystyrene ellipsoids at the water-air interface. By combining interferometry and optical trapping, we directly observe quadrupolar symmetry of the interface deformations around such particles. We then develop numerical solutions of the partial wetting problem for ellipsoids, and use these solutions to deduce the shapes of the corresponding contact lines and the values of the contact angles, theta(c)(k), as a function of the ellipsoid aspect ratio k. Surprisingly, theta(c) is found to decrease for increasing k suggesting that ellipsoid microscopic surface properties depend on ellipsoid aspect ratio.

Computer Simulation↗

PubMed2002

Double emulsions: how does release occur?

Water-in-oil-in-water double emulsions (W/O/W) consist of dispersed oil globules containing smaller aqueous droplets. These materials offer interesting possibilities for the controlled release of chemical species initially entrapped in the internal droplets. A better understanding of the stability conditions and release properties in double emulsions requires the use of model systems with a well-defined droplet size. In this paper, we use quasi-monodisperse double emulsions made of calibrated water droplets and oil globules to investigate the two mechanisms that are responsible for the release of a chemical substance (NaCl). (i) One is due to the coalescence of the thin liquid film separating the internal droplets and the globule surfaces. (ii) The other mechanism termed as 'compositional ripening' occurs without film rupturing; instead it occurs by diffusion and/or permeation of the chemical substance across the oil phase. By varying the proportions and/or the chemical nature of the surface active species it is possible to shift from one mechanism to the other one. We therefore study separately both mechanisms and we establish some basic rules that govern the behavior of W/O/W double emulsions.

Biopolymers↗

PubMed2002

Electrically induced flows in the vicinity of a dielectric stripe on a conducting plane.

We report a theoretical and experimental study of the hydrodynamic flow induced by an a.c. electric field in the vicinity of a dielectric stripe deposited on a conducting plate. In the theoretical part, we model the stripe as a small change of the surface capacitance of the plate, and a perturbative approach is used to perform the calculations. This approach predicts an outwards rectified electro-osmotic slip along the surface that generates two steady counter-rotating rolls, the size of which decreases with the frequency. In the experimental section, we use tracers to determine the structure of the flow and investigate its dependence on the frequency and the amplitude of the applied voltage. The structure and amplitude of the observed flow compares satisfactorily with the theoretical analysis. This could guide the design of surface-controlled flows and help to understand the collective behavior of colloids near electrodes.

Journal Article↗

PubMed2001

Double emulsions: a tool for probing thin-film metastability.

We study the kinetics of the release of monodisperse water-in-oil-in-water double emulsions in the regime dominated by coalescence of the internal aqueous droplets onto the globule interface. By measuring the rate of release of adsorbed droplets, we directly determine the average lifetime of the thin film that forms between the small internal droplets and the globule surface. Therefore, the activation energy and the natural frequency of the hole nucleation process within the adhesive thin liquid films are unambiguously deduced.

Journal Article↗

PubMed2000

Pretransitional effects in dimyristoylphosphatidylcholine vesicle membranes: optical dynamometry study.

We used micron-sized latex spheres to probe the phase state and the viscoelastic properties of dimyristoylphosphatidylcholine (DMPC) bilayers as a function of temperature. One or two particles were manipulated and stuck to a DMPC giant vesicle by means of an optical trap. Above the fluid-gel main transition temperature, T(m) congruent with 23.4 degrees C, the particles could move on the surface of the vesicle, spontaneously (Brownian motion) or driven by an external force, either gravity or the laser beam's radiation pressure. From the analysis of the particle motions, we deduced the values of the membrane hydrodynamic shear viscosity, eta(s), and found that it would increase considerably near T(m). Below T(m), the long-distance motion of the particles was blocked. We performed experiments with two particles stuck on the membrane. By optical dynamometry, we measured the elastic resistance of the membrane to a variation in the interparticle distance and found that it would decrease considerably (down to zero) when the temperature was increased to T(m). We propose an interpretation relating the elastic response to the membrane curvature modulus, k(C). In this scheme, the two-bead dynamometry experiments provide a direct measurement of k(C) in the P'(beta) phase of lipid bilayers.

Biophysical Phenomena↗

PubMed1993

Mammalian cochlear outer hair cells density evaluated by means of an optical tweezer.

We report on the first individual measurements of guinea pig's cochlear outer hair cells densities. Cells were isolated in vitro and manipulated with an optical tweezer. They were levitated in an upward laser beam coaxially trapping the cells. Then they were released by switching off the laser and let fall down in upright position. Measuring their speed and using the Stokes' law, we calculated their mean density. In our experimental frame, the results suggest that the density of the cellular body (between the basal nucleus and the apical cuticular plate) remains quasi constant whatever the cells' length. This implies that density variation of the cellular body does not participate in an intrinsic tuning mechanism.

Animals↗

PubMed1992