Chemistry and Biochemistry SeminarFriday, March 31, 2017 - 4:00pm
Location: Jones Physical Science Center, Room 006
Speaker: Dr. Laura Kaufman
Topic: Single Molecule Approaches to Studying Heterogeneity in Supercooled Liquids
Abstract: Supercooled liquids display behaviors consistent with the presence of heterogeneous dynamics. We investigate the length scales over which such heterogeneities exist and the time scales over which they persist using single molecule (SM) fluorescence microscopy. In previous work, multiple perylene diimide (PDI) probes were employed to investigate whether probe properties affected breadth of heterogeneity reported in the fragile supercooled liquid ortho-terphenyl (OTP) and the less fragile supercooled glycerol. In both cases, the fastest rotating probes reported the greatest breadth of heterogeneity in the host, regardless of physical probe size, suggesting slow probes were averaging over dynamic changes in the environment in time. More recently, we introduced a set of BODIPY-core based probes that are both smaller and more quickly rotating in OTP than the PDI probes. These probes show qualitatively different behavior than the PDI probes, reporting more spatial and temporal heterogeneity than previously studied probes. These measurements showed unequivocally that supercooled liquids are ergodic (where the time average equals the spatial average) down to the glass transition temperature and allowed us to resolve seeming discrepancies between ensemble and single molecule measurements characterizing time scales of heterogeneities in this supercooled liquid. This work has now been extended beyond small molecule glass formers to polymeric glass formers and thin films thereof, systems in which molecules have particularly widely distributed dynamics.
Sponsored by the College of Arts and Sciences and the Department of Chemistry and Biochemistry
Chemistry and Biochemistry Seminar: March 31, 2017