Glass Transitions Of Two-dimensional Granular Dimer Particles

Glass transitions, which is one of the most important problems in natural sciences, has always been the focus of condensed matter research. For molecular glasses, because of the small size of their constitute, such as atoms and molecules, it is very challenging to observe and study them directly. As a result, limited amount knowledge is available on the microscopic behaviors of the glass, and on the physical laws that govern the glass transitions. Granular particles, by contrast, have the advantages of being observed by naked eyes and tunable packing, which offer new model system for the study of the glass transitions. Due to the non-spherical shape and hence the translational and rotational degrees of freedom in dimer particles, the structure and dynamics of dimer glasses are more complex and interesting. So it is of significant importance to study the glass transition of dimer particles.In this paper, we studied the glass transitions of two-dimensional granular dimer particles in an air-fluidized device. Firstly, we observed two glass transitions, namely translational and rotational glass transitions. Secondly, we fitted the relaxation time of translational and rotational motions based on predictions from Mode Coupling Theory(MCT), and find the relaxation times for both degrees of freedom have power-law dependences on packing fraction. In addition, we found the two glass transition points coincide with each other and the two motions are coupled. Last but not least, the cooperative effect of motions was investigated by analyzing the clusters of fastest-moving particles. The cluster sizes of translational and rotational motions both increase upon increasing the packing fraction, and reach the maximum when the system is approaching the glass transition point. In both cases, the probability distribution functions of the cluster sizes obey power-law relations.