Séminaire

Séminaire
Mardi 1er Septembre 2015 à 10h30
Amphithéâtre Henri Benoît
Prof. Dimitris VLASSOPOULOS
FORTH, Institute of Electronic Structure & Laser, and University of
Crete, Department of Materials Science & Technology, Heraklion, Crete,
Greece
Comb and star macromolecules: some rheological consequences of
macromolecular topology
Branching is known to play a key role in the properties of entangled polymers. At the same
time, high level of branching leads to molecular structures such as hyperbranched polymers,
dendritic Cayley-tree types of polymers etc, which can also be viewed as soft colloids. We
discuss our efforts attempting at bridging the interesting gap between polymers and colloids by
accessing highly functionalized well-characterized polymers and exploring their properties with
emphasis on dynamics and rheology. We show two examples. (i) Regular entangled comb
polymers exhibit interesting nonlinear rheological properties in shear (thinning) and uniaxial
extension (hardening). We show that the concept of dynamic dilution provides a framework for
understanding them. (ii) High-molar mass star polymers with changing functionality can
respond as regular entangled stars or soft colloids either in solution or in melt. In solution in
particular they exhibit intriguing properties and their (ultra)softness is responsible for a variety
of new metastable states and transitions at high fractions in molecular or polymeric solvents.
We discuss here an interesting thermoreversible melting phenomenon of a depletion gel in starlinear polymer mixtures. Finally, we close with some thoughts on a relatively new class of
hyperbranched polymers, dendronized polymers. They are similar to bottlebrushes but each
branch is a dendrimer. By varying the molar mass of the backbone and the dendrimer
generation it is possible to switch from polymer-dominated to colloid-like response, hence these
systems offer tunability as well as complexity.
These examples demonstrate that polymer chemistry holds the premise for exploring and
understanding exciting novel properties of soft matter.
Work in collaboration with J. Roovers (Ottawa), N. Hadhichristidis (KAUST), M. Gauthier
(Waterloo), K. Matyjaszewski (Carnegie-Mellon) and A. D. Schlüter (ETH Zürich).
Les personnes souhaitant rencontrer M. Vlassopoulos sont priées de prendre contact avec M. Pierre
Lutz (tel. 03 88 41 40 74 ou mail : [email protected])