Research On Glassy Dynamics And Crystallization Processes In Two-dimensional Colloidal Systems

Phase transition is an important topic in the field of condensed matter physics.Glassy phase can be obtained by increasing the density of the colloidal system.Although there are differences between colloidal hard spheres and atoms in some respects,the behavior of colloidal hard spheres is similar to that of atomic systems during glass transition.Therefore,the colloidal system is a good model system for studying the behaviors of glassy phase and crystallization processes.When the temperature drops rapidly on approaching glass transition temperature,most liquids will reach to glassy state.Structural glasses have long-range disordered amorphous structure.The most remarkable feature of glass transition is the ultra-high viscosity.Although the phenomenon of kinetic slowing down has been extensively studied and many advances have been made,there has not yet a well-accepted physical mechanism that people agrees with.With the development of the optical microscope,molecular dynamic simulation and fast processing large amounts of data,we can directly observe the microscopic dynamic behaviors of colloidal system in glassy state and crystallization processes with the optical microscope and compare the results with the numerical simulation results.In this work,two-dimensional(2D)colloidal systems of the glassy state and crystallization processes were made by means of experiments.We investigated their microscopic dynamic behaviors by direct imaging the colloidal particles and analyzed the large amounts of data.The main contents are as follows:(1)For the 2D glassy colloidal system,the large amounts of sequential position images were analyzed by Matlab software and we obtained trajectory diagrams in different time.By studying the trajectory diagrams in different time,we analyzed the properties and causes of the cooperative rearrangement motions.We made the mean square displacement MSD diagram of the system and analyzed the motion of particles in the system.We made the probability density P(dr/σ)diagrams of the system and analyzed the motion properties of particles in the system.The change of particle hop return and escape with density could explain the slow down of glass state kinetics.(2)For crystallization processes of the 2D colloidal system,the same method as the glassy state system was used to obtain the trajectory diagrams in different time.By studying the trajectory diagrams in different time,the regions of distribution of cooperative rearrangement motions and the change of motion scale with the increase of the system density were analyzed.The MSD diagram and probability density P(dr/σ)diagram of the system were made to analyze the kinematic properties of the colloidal system in the crystallization processes.(3)The trajectory diagrams of the 2D glassy colloidalsystem and the 2D colloidal system in the crystallization were compared.The similarities and differences of their microdynamic behaviors were analyzed,and we explained the reasons for the slow down of the glassy state dynamics.