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Soft matter and biophysics
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Topics :
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Research >
Soft matter and biophysics
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:
Topics :
People
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| Films | How to cook giant bubbles (fête de la science 2002) |
| Through surface tension | Foams | Molecular films | Wetting on disordered surfaces |
Manipulation rather than description :
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… an electric field creates wetted (left) or non-wetted (right) defects ad libitum.
In the same spirit, magnetic manipulation of vertices leads to artificially disordered (left) or ordered (right) foams.
artificially disordered.
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artificially ordered.
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One can artificially force a bubble to change neighbors.
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What is common to foams used in fire fighting, oil extraction, and cosmetics? All fluid foams tend to minimize their surface energy. This determines their mechanical properties. For instance, a foam is elastic at small deformation, and flows under large sollicitations. To understand these limits, as well as the cross-over between them, requires the knowledge of all (metastable) energy minima in which the foam can be stuck. In turn, this raises the mathematicians' problem of finding the minimal surface enclosing a cluster of bubbles of prescribed sizes. We approach this difficult problem by focussing on bidimensionnal foams, using theory, experiments and simulations.
Since the membranes of biological cells are structured around a bilayer of phospholipids, many studies concentrate on their interactions with proteins. We are interested in food proteins, such as ovalbumin and b-lactoglobulin, as well as the short "penetratin" peptide, a potential vector for drug delivery into a cell. Beside monolayers, supported bilayers and vesicles, we have prepared and characterized "free bilayers" in the vicinity of a substrate, stable in time and highly oriented. Since they are fluctuating in excess water, they are also a good system to observe giant consequences of purely physical bilayer-bilayer interactions, especially the so-called "entropic" repulsion due to thermal fluctuations.
The dynamics of spreading of a liquid is often limitated by the existence of an hysteresis between forward motion and receeding of the fluid. The microscopic origin of the hysteresis lies in substrate heterogeneities, as well chemical (variations in surface energy) as physical (roughness) ; but there is up to now very few experiments that would be enough controlled to allow comparison with current theories.
The control of wettability through a modification of the substrate surface energy with an electric field was established recently in the laboratory (http://spectro.ujf-grenoble.fr/focale_variable) ; we adapted this technique in order to obtain surfaces with very few hysteresis (~1°) on which grow defects of controllable amplitude, at will wetted or non wetted. Through this experiment, it will be possible to observe very simply the effect of the amplitude of purely chemical defects on contact angle hysteresis.
| Films | How to cook giant bubbles (fête de la science 2002) |
| Through surface tension | Foams | Molecular films | Wetting on disordered surfaces |
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:
People
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Soft matter and biophysics : Scientific Activity : LSP |