Public Thesis Defense of Maxime DALNE - IMCN

Nonlinear shear rheology of linear polymer melts and solutions: modeling, simulations and experiments

Friday March 20th, 2026 - 3pm - Auditorium SUD03 Place Croix du Sud, 1 - 1348 Louvain-la-Neuve

Despite several decades of research, the rheology of polymer melts remains an active and challenging field, owing to the complex interplay between chain architecture, entanglement dynamics, and flow-induced phenomena. Classical frameworks such as the Rouse model and the tube-based theories of Doi and Edwards have provided a solid foundation for understanding linear viscoelasticity. Building on this, refined models incorporating contour length fluctuations, constraint release, and tube dilation have substantially improved quantitative agreement with experimental observations.

Nevertheless, the description of strongly nonlinear regimes remains incomplete. Phenomena such as stress overshoot, shear thinning, and chain stretching at high Weissenberg numbers are now qualitatively understood, yet their quantitative prediction remains sensitive to model assumptions and parameter choices. Although non-equilibrium molecular dynamics (NEMD) simulations have yielded valuable insights into chain orientation, stretch, and entanglement dynamics, bridging the gap between atomistic or coarse-grained simulations and macroscopic experimental data remains a central challenge in the field.

This thesis addresses the nonlinear shear rheology of polymer melts and solutions across both the unentangled and entangled regimes, through a combined approach of experimental measurements, molecular modeling, and NEMD simulations. This work focuses on understanding the nonlinear shear response of a well-defined monodisperse polystyrene system. By systematically investigating the influence of molar mass, concentration, and shear rate on viscoelastic behavior, a unified molecular picture applicable across all samples is developed. This framework is validated against simulation data and supported by a phenomenological yet quantitatively predictive model derived in this work. Taken together, these results offer new insights into the molecular mechanisms governing nonlinear polymer rheology and demonstrate the power of integrating experiment, simulation, and theory in a coherent and mutually reinforcing approach.

Jury members

Prof. Evelyne van Ruymbeke  (UCLouvain)Supervisor

Prof. Jean-François Gohy  (UCLouvain) Chairperson

Prof. Vincent Legat  (UCLouvain) Secretary

Prof. Dimitris Vlassopoulos (IESL-FORTH, University of Crete)

Prof. Giovanni Ianniruberto (UNINA)

Pay attention : the public defense of Maxime DALNE will also take place in the form of a videoconference