Abstract
Physical aging is an inherent property of glassy matter,but understanding its microscopic mechanism remains a challenge particularly at the particle level.In this work,we use a confocal microscope to in-situ trace the particle trajectories in a 3D colloidal glass for 73000 s,aiming at resolving the aging dynamics.By calculating the mean square displacement of particle motions,we find that the glass aging with time can be divided into three stages:β relaxation,a relaxation and free diffusion.The system's mean square displacement at each aging state is quantitatively resolved into three contributions of particle dynamics modes:vibration within the nearest-neighbor cages,hopping between cages and cooperative rearrangement.We further calculate the particle's free volume and find that the β-to-α transition is accompanied by the temporary increase of the system-averaged free volume due to pronounced hops of particles.Nevertheless,the temporal autocorrelation of the free volume spatial dis-tribution still obeys a monotonically stretched exponential decay with an exponent of 0.76,which is related to the sub-diffusion dynamics of cooperative rearrangements and hops mixed in a relaxation.According to the resolved vibrational displacements,we calculate the vibrational density of states of this 3D glass,and the characteristic boson peak is reproduced at low frequencies.Our findings shed insight into the particle-level aging dynamics of a real glass under purely thermal activation.
基金项目
National Outstanding Youth Science Fund Project(12125206)
Basic Science Center for"Multiscale Problems in Nonlinear Mechanics"(11988102)
General Project of National Natural Science Foundation of China(11972345)
CAS Project for Young Scientists in Basic Research(YSBR-096)
维普
万方数据