Séminaires Exceptionnel
"Matière et Systèmes Complexes"


Mardi 20 mai 2008 à 14h
Bâtiment Condorcet, 6ème étage, salle 646 A.

T. Kajiya and T. Yamagushi
(Department of Applied Physics, The University of Tokyo)

Coffee stain phenomenon in polymers, and sliding friction of an adhesive gel

Two 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.