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Hemmerle, Arnaud

PhD (2010-2013)

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Arnaud Hemmerle has actually a position at synchrotron SOLEIL .

email: arnaud.hemmerle[at]ics-cnrs.unistra.fr


Research activities

My PhD work is devoted to various aspects of the physics of lipid membranes, under the supervision of Thierry Charitat (ICS Strasbourg) and Jean Daillant (CEA Saclay/ SOLEIL Synchrotron). I am currently working on fluctuations and destabilization of phospholipid membranes studied by small angle X-ray specular and off-specular scattering, and focusing especially on inter bilayers interactions.

Understanding interactions between membranes requires measurements on well-controlled systems close to natural conditions, in which fluctuations play an important role. Few years ago, our team developed a model system with a nearly free bilayer "floating" above a strongly adsorbed one. Thanks to the power of the ESRF European synchrotron, we are now able to measure precisely the interaction potential between two phospholipidic bilayers, by studying the way X rays are scattered by the bilayer fluctuations.

We find that interactions in this highly hydrated model system are two orders of magnitude softer than in previously reported work on multilayer stacks. This is attributed to the weak electrostatic repulsion due to the small fraction of ionized lipids in supported bilayers with a lower number of defects. We also have unique access to very weak entropic repulsion potentials, which allowed us to discriminate between the various models proposed in the literature. Indeed, since W. Helfrich discovered the importance of fluctuations in membrane interactions, many models have been proposed to describe the effects of confinement, while only a few experiments have been performed close to model conditions.
We further demonstrate that the interaction potential between supported bilayers can be tuned at will by applying osmotic pressure, providing a way to manipulate these model membranes, thus considerably enlarging the range of biological or physical problems that can be addressed.