Rejuvenation and Memory Effects in WCA Systems: A Free-Volume Perspective on Hierarchical Relaxation Dynamics

This study offers a comprehensive analysis of the rejuvenation and memory effects observed during temperature cycling in five-component Weeks–Chandler–Andersen (WCA) systems, utilizing molecular dynamics simulations. We investigate the molecular mechanisms driving these effects from a free volume perspective. Our findings reveal that dynamical processes and structural evolution at varying temperatures operate independently across multiple spatiotemporal scales, thereby highlighting a distinct decoupling of multiscale dynamics within glassy systems. Notably, while the total free volume remains constant over time, a pronounced peak in large free volume is observed during the second stage of temperature cycling. This peak is intricately linked to the aggregation of free volume, a key factor facilitating rejuvenation dynamics. Furthermore, our analysis shows that free volume aggregation primarily occurs in localized regions, which corresponds to the activation of secondary potential wells within the energy landscape. Critically, this process develops independently of large-scale structural changes, thus preserving the system’s memory effects. By emphasizing the crucial role of free volume in the emergence of marginally stable phases and rejuvenation phenomena, this study advances the theoretical understanding of non-equilibrium dynamics and provides valuable molecular insights into the complex physical behaviors inherent to glassy states.