Vitrimers are now commonly considered as the third class of polymer materials alongside thermoplastics and thermosets. At service temperature, vitrimers behave like traditional thermosets, with good mechanical characteristics but can be recycled, reshaped at high temperature similarly to glass. This discovery opens new green perspectives such as crack repairing, correction of moulding defects and depolymerisation/recycling using soft conditions. Nonetheless, the transfer from academia toward industry is not straigthforward and require extensive collaborative efforts from scientists and engineers in chemistry, materials science and engineering.

Our understanding of the mechanism by which the viscosity of supercooled liquids increases by many orders of magnitude is often described as a major challenge in condensed matter physics [1,2]. It is therefore necessary to discriminate between seemingly incompatible theoretical approaches which provide equally good descriptions of experimental data: a scientific revolution [3]. Much of the perceived incompatibility revolves around whether the glass transition is driven by underlying thermodynamics or is predominantly a dynamical phenomenon. Here we report new results with experiments and simulations which explore previously inaccessible dynamical regimes at the single-particle level [4,5], where we test explicitly the predictions of each approach. We find that the predictions of both thermodynamic and dynamical approaches are upheld and suggest routes out of the scientific revolution of the glass transition.
While the glass transition hard spheres may be somewhat understood, addition of a short-ranged attraction (sticky spheres) results in far-from-equilibrium behavior: aging leads to a change in mechanical properties over time. Remarkably, these “stronger” gels can then undergo spontaneous catastrophic failure with tremendous consequences for the many materials that rely on gelation [6]. We show how this dramatic and counter-intuitive phenomenon may be predicted in a newly-developed experimental system where forces between particles may be resolved [7].

[1] Royall, C. P. & Williams, S. R. “The role of local structure in dynamical arrest”, Phys. Rep. 560 1-75 (2015).
[2] Royall, C. P., Turci, F., Tatsumi, S., Russo, J. & Robinson, J. “The race to the bottom: approaching the ideal glass?”, J. Phys.: Condens. Matter 30 363001 (2018).
[3] Kuhn, T. S. The Structure of Scientific Revolutions Univ. Chicago Press, 1962.
[4] Hallett, J. E., Turci, F and Royall, C. P. “Local structure in deeply supercooled liquids exhibits growing lengthscales and dynamical correlations”, Nature Commun. 9 3272 (2018).
[5] Ortlieb L, Ingebrigtsen TS, Hallett JE, Turci F and Royall CP “Relaxation in supercooled liquids: Cooperatively Re–arranging Regions vs Excitations”, ArXiV 2103.08060 (2021).
[6] Royall CP, Faers MA, Fussell SL and Hallett JE, “Real Space Analysis of Colloidal Gels: Triumphs, Challenges and Future Directions”, J. Phys.: Condens. Matter, 33 453002 (2021).
[7] Dong J, Turci F, Jack RL, Faers MA and Royall CP, “Direct Imaging of Contacts and Forces in Colloidal Gels” J. Chem. Phys. 156 214907 (2022).