Glassy Dynamics, from Molecules to Cells

We investigate complex systems in which jamming occurs; this phenomenon is characterized by abrupt dynamical arrest upon changes in properties such as temperature or density. In particular, we focus on jamming and the glassy dynamics that precede jamming in supercooled molecular liquids and cells in crowded environments. In supercooled liquids, one key unanswered question is how jamming is causally related to glassy, heterogeneous dynamics and collective molecular motion. We study these molecular systems with single molecule imaging, as such experiments are the only ones capable of directly interrogating the length and time scales of interest. Specifically, we measure rotations of single fluorescent probes in high molecular weight polystyrene in the supercooled regime to characterize the time scales over which heterogeneities persist in this system. Additionally, aiming to resolve long-standing questions regarding the origins of a phenomenon known as rotational-translational decoupling, we combine rotational and translational measurements, and show that the observed phenomenon is not purely an artifact of averaging over an ensemble of molecules. Beyond such molecular systems, we study glassy behavior and jamming in biological systems, where, perhaps surprisingly, some of the same interesting and poorly understood dynamics that appear in supercooled liquids also appear, with particular relevance in development and cancer. We combine experiments and minimal computational models to study these dynamics, with computational approaches allowing us to isolate key variables that may effect cell jamming and unjamming. We find cell shape to be both a critical marker and maker of cell mobility in densely packed environments, with key differences in degree of collective motion as a function of cell shape, a finding that may apply more broadly across systems that display glassy dynamics and undergo jamming.