The Structure of Fluid and Glassy Systems at Short Time and Length Scales

Abstract

All constituent particles of material at non-zero temperature undergo ballistic motion at a short enough timescale. At longer times the particles begin to interact with the other constituent particles forcing them to transition out of the ballistic regime. The manner in which a particle transitions out of ballistic motion is a useful probe of the micro-scale material structure. Here, I develop an experimental setup that allows me to track a particle with sufficient spatial and temporal resolution to distinguish the ballistic motion and the subsequent transition to the long time structural behavior. I verify this technique by analyzing the motion of a freely floating colloid in water and comparing it's ballistic diffusive transition to the accepted behavior for a Newtonian liquid. I extend this treatment to a colloid suspended in a Maxwell fluid. I prove that the liquid's micro-scale behavior is qualitatively the expected behavior for a Maxwell liquid while deviating significantly from the quantitative picture. Next, I examine the motion of a colloid within a dense colloidal glass. I demonstrate that there are three different structural behaviors present in the system depending on the packing density. Further, these different phases precisely align with those predicted by the replica theory of glasses for a dense liquid, a stable glass, and a marginal glass. This constitute the first experimental proof of the existence of a marginal glass and an important confirmation of the replica theory of glasses. This work also begins to experimentally map the colloidal glass phase diagram revealing a reentrant stable glass phase space.