Dimitris Vlassopoulos

University of Crete and IESL-FORTH

Chemical Engineer

Awarded Bingham Medal 2019

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.