Evelyne van Ruymbeke
Université catholique de Louvain
Fellow, Elected 2023
Van Ruymbeke has studied polymer rheology in many contexts, embracing modeling and experiments. Her overall objective has been the development of strategies to explore the rheology
of complex macromolecular materials, based on design and use of well-characterized systems and mesoscopic modeling, linking molecular architecture to flow, to obtain powerful predictive
tools. Key accomplishments are briefly outlined below:
She has developed a highly versatile coarse-grained model for describing the linear rheology of linear and branched macromolecules of varying complexity, including randomly branched
and polydisperse polymers. Today, the “time marching algorithm” (TMA), is universally acclaimed. Among its advantages is the parameter-free description of the branch point hopping
mechanism based on a wise choice of the molecular coordinate system. To model the dynamics of polydisperse branched macromolecules, as well as sticky polymer chains, van Ruymbeke
has developed and validated a Monte Carlo approach to build the statistical composition of a sample, based on its synthesis and molecular characterization details. It allows to
describe the composition of sticky chains or supramolecular assemblies, from the association probabilities of reversible junctions. This powerful approach has been implemented to
both model and industrial branched and associating polymeric materials.
Van Ruymbeke has proposed a new molecular picture to explain the response of entangled polymer chains to uniaxial extension with particular focus on the experimentally observed elongational
thinning of polymer melts. According to this approach, at a given elongational strain rate the chains reach a maximum stretch level, which arises from the balance between chain retraction
(induced by the monomeric tension equilibration along their backbone) and chain elongation (induced by the flow). By incorporating this mechanism into TMA, she reached quantitative comparison
with state-of-the-art experimental data from her laboratory and from the literature, for nearly monodisperse linear polymer melts over a range of stretch rates and molar masses.
Van Ruymbeke has recognized that the complexity of supramolecular polymeric networks, which exhibit multiscale dynamics, necessitates the use of well-defined polymeric building blocks and
the combination of careful experiments with targeted modeling in order to understand their structure-rheology interplay. With the help of chemists she has designed and obtained model materials
with varying interactions (hydrogen bonding, metal-ligand, amphiphilic, ionic interactions) for tuning their organization and dynamic response, and tackled fundamental open questions,
in particular understanding the effects of the associating groups and the internal dynamics of the building blocks on rheology, both in solution and melt state.