Dr. Eric Weeks
Department Chair and Samuel Candler Dobbs Professor, Department of Physics
We use microscopy to study both 3D and quasi-2D colloidal systems as they approach their glass transitions as their concentrations are increased. We examine a 3D hard-sphere-like system, a 2D hard-sphere-like system, and a 2D soft-sphere system. All samples are bidisperse to frustrate crystallization. We measure the relaxation time scales for translational motion and structural reorientation, both of which dramatically increase as the glass transition is approached. A strong contrast is seen between the 2D and 3D data close to the glass transition, in that structural reorientation is markedly slower in 2D than in 3D. This is due to coordinated particle motion where particles move significant distances without changing their positions relative to their neighbors. By considering only motion relative to one's neighbors, the two relaxation time scales agree much better in both 2D and 3D. Overall, our results agree with recent simulation results [Flenner and Szamel, Nature Communications 2015] in that 2D and 3D glass transitions appear qualitatively different, but we extend their observations and suggest that the differences are removed upon adjusting the measurement method.