Physical Chemistry

The group of “Soft Interfaces” contributes to the advancement of knowledge on wetting, adhesion, polymers at interfaces, mechanical properties of cells and membranes, motility and transport, and microrheology. We are chemical physicists working in the field of experimental and theoretical soft matter, with a close collaboration with industry for many of our projects.

Wetting and dewetting

In the field of wetting, we study the fluctuations (triplons) of floating contact lines, and the parametric instability of vibrated droplets, the fast dewetting of a floating liquid film, which gives rise to a cascade of shocks, and the parametric instabilities of drops oscillating vertically. In collaboration with St. Gobain, we make and characterize antifrost and antifog substrates. We also study the spreading of vesicles on substrates, both decorated with receptor-ligand proteins. This involves dewetting of the intercalated liquid film coupled to proteins diffusion. For living cells, the spreading is controlled by the viscoelasticity of the cytoskeleton. To test this model, we study the spreading of a silly putty ball both on smooth and patterned surfaces (movie 1).

Fig.1: Formation de motifs sur un film polymère refroidi puis exposé à une atmosphère humide
   

Adhesion and friction

In collaboration with A. Buguin (UMR 168), we have built a macro-AFM coupled to contact imaging (by optical interferometry) to study the adhesion and the friction of rubber-beads (col. Michelin), vesicles, and cells to smooth or rough substrates. We investigate the dynamics of contact formation and of detachment for specific-nonspecific adhesion, friction and “specific” friction, and stick-slip phenomena, both experimentally and theoretically.

Fig.2: Le détachement d'une bille d'une surface en verre. De gauche à droite : la bille s'éloigne du substrat (film 2).

On “pillar” substrates two contact states are observed as a function of heights of the pillars (fig. 3). We can induce a transition between full to partial contact under shear (movie 3).
Used techniques are RICM, Macro-AFM, Wet JKR.
Fig.3: Contact sur une surface à motifs. a) image MEB (microscopie électronique à balayage) d'une surface microstructurée, b) contact intime entre une bille à base de PDMS et la surface à motifs sur laquelle elle s'appuie, c) plus la hauteur des piliers augmente, plus le contact de la bille est posé.
In collaboration with the group Systems Cell Biology of Cell polarity and Cell division, we study the role of stretching of an elastic substrate on cell division. We also start a new collaboration with D. Fletcher's group at U. C. Berkley to investigate the impact of liquid jets at decorated interfaces, which are used to produce vesicles enclosing active agents.

Cellular nanotubes / Cell feelers

We use hydrodynamic tether extrusion to study the mechanical properties of lipid membranes of impermeable and porous giant unilamellar vesicles, and living cells (red blood cells, murine sarcoma S180 cells, human carcinoid BON cells - movie 4). In collaboration with the Unit Subcellular structure and cellular dynamics, we study the role of E-cadherin on membrane-cortex interaction using nanotube extrusion. For cells, we measure the membrane/cytoskeleton adhesion, the traffic of lipids (col. E. Karatekin), and the role of drugs on tether extrusion. We also investigate artificial cells: vesicles enclosing, biological gels (col. C. Sykes, UMR 168) and synthetic gels (col. A. Viallat - Univ. Aix-Marseille 2, B. Pépin-Donat - CEA, Grenoble). Using these jelly vesicles, we can vary the density of binders linking the membrane to the cytoskeleton and test the theoretical model developed to interpret the dynamics of fast extrusion of cellular nanotubes. We also interpret the transport in nanotubes as a Marangoni effect in collaboration with J. F. Joanny.

Fig.4: Extrusion hydrodynamique de tubes. a) vésicules encapsulant un gel de poly(N-isopropylacrylamide), b) vésicules encapuslant un cortex d'actine, c) extrusion de tubes à partir de globules rouges.

Microfluidics

In microfluidics, we have studied the confinement and the passage of cells and macromolecules (DNA) in microscopic pores under a flow or an electric field for DNA (work initiated by P. G. de Gennes). We have also studied transport in lipidic nanotubes, which may also be used to fabricate nanodevices connecting microreactors (vesicles or cells).