Study On The Dynamics Of Two-dimensional Glassy State Transition And Glass Properties In Polycrystalline Systems

Solids can be basically classified into two groups,glass,and crystal.They have been studied as two separate fields for a long time.Colloidal particles have similar physical properties as atomic crystal and glass,and they are often used to study crystallization,melting and glassy dynamics.The glassy system has a disordered structure,while the polycrystalline system has a semi-disordered structure.Although both glassy and crystalline materials had been widely studied for a couple of decades,there are still many controversies in the theories describing the transition from the supercooled liquid state to glassy state,particularly,the primary reason for kinetic arrest of glassy system and kinetic problems in polycrystalline materials at the microscopic particle level are still unclear.Uniform colloidal microspheres dispersed in a solvent will,under appropriate conditions,self-assemble into ordered crystalline structures.it has been demonstrated that point defects can be created in two-dimensional colloidal crystals by manipulating individual particles with optical tweezers to study the dynamics of vacancy.In this work,we based on the observation of particles in the two-dimensional colloidal system under an optical microscope,through image processing and Molecular Dynamics(MD)simulation,to study the dominant relaxation in the deeply supercooled glassy and polycrystalline system by tracing particles’ trajectories at the long-time limit.We found that for the glassy system,the motion of the particles experienced a transition from a collective to a string-like hopping motion as it approached the glass transition.We also found that the α relaxation in the glass transition is mainly due to the string-like hopping motion.More interestingly,we found that the strings are induced by quasi-voids,which trigger the relaxation of the colloidal glasses.Particles participate in the successive string-like hopping motions in the same region that can be grouped into the same mobile cluster,and we found that these mobile clusters have sizes increased monotonously when approaching the glass transition point.In addition,the string-like hopping motion has a very high returning hop probability and a small escaping hop probability near the glass transition,resulting in long-term ultra-slow relaxation.Our findings reveal the physical origins of the kinetic stagnation of colloidal glass in glass transitions and thus constitute a critical step in understanding the physics of glass dynamics and the problem of interference.We also found that single vacancy and double vacancies in polycrystalline materials have strong memory effects.The vacancy movement in a single crystal is uniform in all directions.We speculate that it will slowly migrate to the grain boundary over time,while the other crystal structure is crystalline but the dynamic characteristics are disordered and have glassy properties,which is called glassy-polycrystalline.We believe this discovery has laid the foundation for further studies of the glassy dynamics.