Reentrant Glass Transition and Cooperative Dynamics in Quasi-Two-Dimensional Attractive Colloidal Suspensions

Reentrant glass transition in hard spheres systems with short-range attractions are nonmonotonic phase transitions due to the competition between repulsive and attractive forces. This phenomenon has been extensively studied in three-dimensional (3D) systems. We experimentally study the dynamics of quasi-two-dimensional (2D) bidisperse colloidal glasses using optical microscopy and particle tracking techniques. The inter-particle attractions are induced and tuned in-situ using nanometer-size micelles. As the attraction strength increases, the reentrant transition from repulsive glass to supercooled liquid and then to attractive glass is observed from ensemble dynamical quantities including mean square displacements and self-intermediate scattering functions. Contrary to studies in 3D systems, ergodic fluid is absent from our 2D experiment, suggesting a difference due to dimensionality. Moreover, the heterogenous dynamics is examined by both dynamical susceptibilities and cooperative rearrangement regions along the reentrant glass transition line; both measurements suggest dynamics becomes the most heterogeneous in supercooled liquid state, which is also distinctive from 3D systems.