Anton Smessaert | Searcharxiv

arXiv2015

Correlation between rearrangements and soft modes in polymer glasses during deformation and recovery

We explore the link between soft vibrational modes and local relaxation events in polymer glasses during physical aging, active deformation at constant strain rate, and subsequent recovery. A softness field is constructed out of the superposition of the amplitudes of the lowest energy normal modes, and found to predict up to 70% of the rearrangements. Overlap between softness and rearrangements increases logarithmically during aging and recovery phases as energy barriers rise due to physical aging, while yielding rapidly rejuvenates the overlap to that of a freshly prepared glass. In the strain hardening regime, correlations rise for uniaxial tensile deformation but not for simple shear. These trends can be explained by considering the differing degrees of localization of the soft modes in the two deformation protocols.

cond-mat.soft↗

arXiv2013

Distribution of local relaxation events in an aging 3D glass: spatio-temporal correlation and dynamical heterogeneity

We investigate the spatio-temporal distribution of microscopic relaxation events, defined through particle hops, in a model polymer glass using molecular dynamics simulations. We introduce an efficient algorithm to directly identify hops during the simulation, which allows the creation of a map of relaxation events for the whole system. Based on this map, we present density-density correlations between hops and directly extract correlation scales. These scales define collaboratively rearranging groups of particles and their size distributions are presented as a function of temperature and age. Dynamical heterogeneity is spatially resolved as the aggregation of hops into clusters, and we analyze their volume distribution and growth during aging. A direct comparison with the four-point dynamical susceptibility χ4 reveals the formation of a single dominating cluster prior to the χ4 peak, which indicates maximally correlated dynamics. An analysis of the fractal dimension of the hop clusters finds slightly non-compact shapes in excellent agreement with independent estimates from four-point correlations.

cond-mat.soft↗