"Matière et Systèmes Complexes"
20 mai 2008 à 14h
Bâtiment Condorcet, 6ème
étage, salle 646 A.
stain phenomenon in polymers, and sliding friction of an adhesive gel
problems will be adressed in this talk.
- (1) In the drying process of polymer solution droplet, we established
an experimental procedure for visualizing solute volume fraction
profile via fluorescent microscopy and lateral profile observation.
Coffee stain effect, the phenomenon that solute polymer converges to
the edge because of the outward capillary flow, was dynamically
observed. We found that strong solute transport moves out most of
polymer which was originally suspended near the center, which makes
solute concentration almost constant until the late time of drying. We
also conducted the analysis of evaporation rate effect for the
dynamics, and confirmed solute transport via the outward flow is
restrained in case of slow evaporation.
- (2) We report studies on the sliding friction of a soft and sticky
gel-sheet on a rigid substrate. The gel does not slip at the
gel-substrate interface and the sliding is caused by the propagation of
detachment waves which are similar to the Schallamach wave or
self-healing slip pulse but follow different mechanisms. The sliding
pattern exhibit a clear velocity dependence: a regular stripe-like
pattern at large sliding velocity, and irregular bubble-like at small
sliding velocity. We develop a model to explain the velocity dependence
of the frictional force, and discuss the mechanism responsible for the
instability of the stripe patterns.