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Mardi 27/03/2007 - 14H00

Soft Matter in Motion

Roland Netz (Technische Universität München, chaire de Matière Molle et Biophysique)

par Didier Poilblanc - 27 mars 2007

The dynamics of soft matter combines the fields of non-equilibrium thermodynamics, elasticity theory and hydrodynamics. Theoretical approaches thus combine molecular simulations, continuum modeling and scaling approaches. This is demonstrated with a few examples :
- Spider silk consists of polypeptides with highly repetitive motives and readily adsorbs on hydrophobic and hydrophilic surfaces. Single molecule AFM studies yield adsorption energies and point to an extremely high mobility on hydrophobic surfaces. Atomistic MD simulations show that binding and high mobility are related to the interfacial water structure at hydrophobic surfaces.
- Shear-flow induced unfolding of proteins plays an important role in starting the coagulation cascade in small blood vessels. In the theoretical modeling the unfolding is initiated by single-chain protrusion-like excitations and leads to a hydrodynamic unfolding transition, which is well captured by a scaling nucleation argument.
- Bacteria have developed propulsion mechanisms well adapted to the low-Reynolds number environment in a cell. The helical flagella of Salmonella and E. coli are well known. Here we characterize the motion of Spiroplasma, a very small and primitive bacterium that has a helical body and drives itself by continuously sending waves of domain walls between right and left handed helicity down its body.