Measuring Dynamic Heterogeneity in Supercooled Liquids

Speaker: Jack Stropko, Boston University, Physics Department

When: February 23, 2021 (Tue), 02:00PM to 03:00PM (add to my calendar)

This event is part of the Preliminary Oral Exam.

Glasses are amorphous materials formed from supercooled liquids which behave mechanically like solids. The mechanism of the transition from supercooled liquid to glass is one of the oldest unsolved problems in condensed matter physics. A natural question is whether one theory can describe this transition among the huge range of glass-forming materials. Thus far no thermodynamic phase transitions have been detected to explain the molecular slowdown in glass formers. However, it is now known that dynamic fluctuations in molecular diffusion, called dynamic heterogeneities, arise as liquids are cooled toward the glass transition temperature. The length scale of dynamic heterogeneities grows with decreasing temperature, but direct measurement has proven to be a challenge, as the dynamics must be resolved in space and time at very small scales. Stable point defects in diamond called nitrogen vacancy (NV) centers can be used to study molecular dynamics to better understand how dynamic heterogeneities form. We have designed and built an NV detection setup with a special low-temperature sample chamber to probe supercooled liquids near the glass transition. I will discuss NV measurement schemes for estimating dynamic correlation lengths in supercooled liquids.