Dimitris Vlassopoulos
University of Crete and IESL-FORTH
Chemical Engineer
Fellow, Elected 2018
Professor Vlassopolous has provided molecular insights into the rheology of polymers and soft colloidal suspensions. By devising strategies based on molecular design of model systems with adaptable
molar mass and architecture, or tunable interactions (from hard to ultrasoft), and developing appropriate protocols and rheometric tools he investigated systematically their linear and nonlinear
rheology.
Examples of key contributions include: (i) the power-law stress relaxation of entangled ring polymers, setting them apart from any other polymer with free ends, and the extreme sensitivity of
their dynamics to traces of unlinked polymeric chains; (ii) multiarm star polymers have been established as model soft colloids with tunable interactions depending on their functionality. Along
with microgels they encompass all features of softness (shape adjustment and interpenetration) that affect their rheology. Their mixtures with linear homopolymers or other colloids exhibit an
unprecedented richness of state behavior and viscoelastic response, enabling the design of soft composites with tunable properties; (iii) architectural dispersity, i.e., the distribution of
molecular structure in branched polymers, which is inevitable even when the most accuracy synthetic protocols are used, has been identified as a crucial element for carefully assessing or improving
molecular constitutive equations, and ways to control it have been devised; (iv) the exact role of branches (number, size, distribution) in complex polymers (such as model combs) on their hierarchical
viscoelastic relaxation, transient shear response (exhibiting two-peak stress) and extension hardening has been revealed and quantified; (v) rheometric advances (in particular cone-partitioned
plate setups) have provided unique nonlinear rheological information (shear, first and second normal stress differences) which has substantially enhanced our understanding of linear, branched
and cyclic polymers and nanocomposites.