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19 06 11 Prof. Stuart PRESCOTT

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UNSW, Sydney, Australie

"How do polymers behave in small spaces?"
mardi 11 juin 2019 à 10h

Campus Jussieu
Barre 43-53, 5e étage, salle 522

The solvent-mediated forces between macromolecular structures at surfaces are the essence of the physics of adhesion, steric stabilisation of colloids, tack in rubbers, biofouling, lubrication and many other problems in particle aggregation and coalescence. Colloidal systems are heavily dependent on these forces and the polymers that are adsorbed or grafted to particles can either enhance the stability of colloidal dispersions or promote aggregation.

We have combined a surface force type apparatus with neutron reflection to measure the structure of polymer brushes in confined geometries. Our system mimics the collision between two particles or surfaces, with the geometrical confinement leaving the polymer molecules trapped between the impinging interfaces. The polymers are highly perturbed by the confined geometry while the solvent is free to leave.

Contrary to expectations, we find that polymer brushes collapse under relatively small applied loads; steric stabilisation of colloids by polymers is substantially weaker than than imagined. We also find that the degree of interpenetration of polymers as the surfaces impinge can be tuned by using polymers that are responsive to pH.