Université libre de Bruxelles

报告摘要：

The properties of an ensemble of objects far from thermodynamic equilibrium change over time. The transformation of buds into flowers and fruits, tectonic plate movements, and even the whole human body over its lifetime are just a few, among the many, examples of such non-equilibrium systems.

According to Onsager’s regression hypothesis, the macroscopic relaxation of a non-equilibrium system (dissipation) obeys the same laws of molecular dynamics in equilibrium conditions (spontaneous microscopic fluctuations). In liquids, such equilibration is usually driven by the so-called α-modes, which are responsible for density fluctuations and become increasingly slow upon cooling. However, recent evidence reveals an alternative pathway with a nearly temperature-independent activation barrier (~100 kJ/mol).

We identified this alternative pathway as the slow Arrhenius process (SAP), detected through dielectric spectroscopy. The SAP is described by the collective small displacements (CSD) model, in which local amorphous packing is reshaped by molecular motions smaller than those involved in α-modes. Based on a statistical mechanics-derived equation of state, the CSD model predicts the SAP’s activation energies a priori, using only thermodynamic analysis of material properties.

Finally, based on the experimental findings collected so far on polymers and small molecules, we present a new framework for the equilibration of materials. And we demonstrate that our model is capable to provide quantitative predictions on properties of technological interest as the adsorption rate of polymers on silicon wafers and the crystal growth rate of small organic molecules in the glassy state.

报告人简介：

Dr. Simone Simon Napolitano is a full professor at the Faculté des Sciences, Université libre de Bruxelles (ULB), Belgium. He completed his Ph.D. in physics at KU Leuven in 2008, followed by a postdoctoral fellowship granted by the FWO. Since 2011, he has been a member of the Faculty of Science at ULB, where he created the Laboratory of Polymer and Soft Matter Dynamics in 2013. In 2019, he joined the Experimental Soft Matter and Thermal Physics Laboratory of ULB. Dr. Napolitano is an experimental soft matter physicist specializing in the investigation of molecular mobility. By studying molecular motion across different length and time scales, he aims to identify physical methods—such as fast processing or nanoconfinement—that can enhance material performance without altering chemical composition. He has published 87 papers in leading journals (e.g., Nature Communications, Science, Science Advances, PRL), with an h-index of 42 and over 5,400 citations. His honors include the 2012 Pieter Debye Prize and repeated inclusion in Elsevier’s Top 2% Scientists list.

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