Intermittent dynamics and logarithmic domain growth during the spinodal decomposition of a glass-forming liquid

Abstract

We use large-scale molecular dynamics simulations of a simple glass-forming system to investigate how its liquid-gas phase separation kinetics depends on temperature. A shallow quench leads to a fully demixed liquid-gas system whereas a deep quench makes the dense phase undergo a glass transition and become an amorphous solid. This glass has a gel-like bicontinuous structure that evolves very slowly with time and becomes fully arrested in the limit where thermal fluctuations become negligible. We show that the phase separation kinetics changes qualitatively with temperature, the microscopic dynamics evolving from a surface tension-driven diffusive motion at high temperature to a strongly intermittent, heterogeneous, and thermally activated dynamics at low temperature, with a logarithmically slow growth of the typical domain size. These results elucidate the microscopic mechanisms underlying a specific class of viscoelastic phase separation.

Ultra-long-range dynamic correlations in a microscopic model for aging gels

“…A more recent work on a low density gel reported instead subdiffusive behaviour [37]. At a more coarse-grained level, it was suggested that localised bondbreaking events in gels may result in compressed exponentials [38], a mean-field scenario that was recently revisited using a mesoscopic elasto-plastic model for generic glassy materials [39], in which the gel structure however plays no direct role.Using large-scale numerical simulations of a particlebased model for gel formation [13,14], we show that the spontaneous microscopic aging dynamics during gelation possesses all anomalous signatures reported experimentally. We find a subdiffusive aging dynamics at short lengthscales, corresponding to caged particle motion inside the gel strands, crossing over to superdiffusive relaxation at larger lengthscales triggered by intermittent snapping of the fractal network.…”

“…Using large-scale numerical simulations of a particlebased model for gel formation [13,14], we show that the spontaneous microscopic aging dynamics during gelation possesses all anomalous signatures reported experimentally. We find a subdiffusive aging dynamics at short lengthscales, corresponding to caged particle motion inside the gel strands, crossing over to superdiffusive relaxation at larger lengthscales triggered by intermittent snapping of the fractal network.…”

“…On the other hand at very low temperatures, the gelation process is essentially arrested, because the particle bonds become nearly permanent. A detailed characterization of the gel structure can be found in [14]. Below we explore the intermediate, experimentally relevant regime where the gel evolves very slowly with time, focusing on the temperature T = 0.15.…”

“…A prevalent method to form physical gels follows a nonequilibrium route by quenching a homogeneous fluid into a phase coexistence region [1,[7][8][9][10][11][12], which generates bicontinuous structures. When the dense phase forms an amorphous solid, the phase separation is kinetically hindered [13][14][15][16] and a gel forms. The microscopic dynamical and structural properties of these nonequilibrium gels evolve slowly with time.…”

“…Following previous work [13,14], we study the properties of a binary Lennard-Jones mixture after it is suddenly quenched into its liquid-gas phase coexistence region. To access large-enough system sizes, we work in two spatial dimensions.…”