Universal scaling in the aging of the strong glass former SiO2

Abstract

We show that the aging dynamics of a strong glass former displays a strikingly simple scaling behavior, connecting the average dynamics with its fluctuations, namely, the dynamical heterogeneities. We perform molecular dynamics simulations of SiO2 with van Beest-Kramer-van Santen interactions, quenching the system from high to low temperature, and study the evolution of the system as a function of the waiting time tw measured from the instant of the quench. We find that both the aging behavior of the dynamic susceptibility χ4 and the aging behavior of the probability distribution P(fs,r) of the local incoherent intermediate scattering function fs,r can be described by simple scaling forms in terms of the global incoherent intermediate scattering function C. The scaling forms are the same that have been found to describe the aging of several fragile glass formers and that, in the case of P(fs,r), have been also predicted theoretically. A thorough study of the length scales involved highlights the importance of intermediate length scales. We also analyze directly the scaling dependence on particle type and on wavevector q and find that both the average and the fluctuations of the slow aging dynamics are controlled by a unique aging clock, which is not only independent of the wavevector q, but is also the same for O and Si atoms.

Mapping Isobaric Aging onto the Equilibrium Phase Diagram

“…Thus there is no explicit dependence on time and we can write log(γ(t)) = log(γ(V(t), T)) during isobaric aging. This indicates that if there are dynamical heterogenities and/or local fluctuations in the dynamics then these all age in the same way as "slaves" of the global clock rate γ(t) in agreement with earlier findings [29,34]. Now we can consistently define the out-of-equilibrium relaxation time as one over the rate τ(t) = 1/γ(t) and analyze how τ(t) depends on the state of the liquid.…”

Real-space model for activated processes in rejuvenation and memory behavior of glassy systems

“…The morphology of energy landscapes in high-dimensional configuration spaces is at the heart of complex dynamics for a broad range of statistical systems. 1,2 Examples are legion in disparate systems: glassy materials like amorphous fluids, 3 jammed grains, 4,5 colloids, 6,7 disordered magnets, 8,9 crumpling sheets, 10,11 or entangled polymers, [12][13][14][15] all face frustration while relaxing their free energy. Due to competing variables exerting geometric or energetic constraints on each other, a complex, multimodal landscape is imposed on the space of all possible configurations.…”

“…A standard approach to gain insight into the complexity of the landscape of a glassy system, whether in experiment or in simulation, is through a hard quench 12 from the liquid-like high-temperature (or low-density) to a low temperature (or high density) regime, initiating a non-equilibrium relaxation dynamics known as aging. 3,5,[16][17][18][19][20][21][22][23][24][25][26][27][28] Such a quench takes the system instantly deep into the glassy landscape. There, a hierarchy of barriers emerges that quite naturally calls for an effective description of the ensuing dynamics in terms of a sequence of activated events that is called record dynamics (RD), 29 since that hierarchy renders all but the largest fluctuations ineffectual and relaxation is characterized by timescales for barrier crossings that exceed all others.…”