Department of Chemistry
University of Pennsylvania
Understanding Glass Transition Through Interfacial Properties
Glass transition, the process of falling out of equilibrium for a super-cooled liquid, has long been a topic of intense theoretical work. Few experiments can be performed to probe properties of glasses in the dynamical range relevant to distinguish these theories. It has been shown that interfaces, in particular the free surface of a glass strongly perturb the dynamics of glasses, such that the relaxation time at the free surface can be 8-10 decades faster, affecting properties over ~30 nm into the material. The origin of this phenomenon and the extent to which it affects the properties of a glass can provide a window of opportunity to evaluate predictions provided by well-stablished glass theories. In this presentation, I will discuss the results of experiments on various polymeric and small molecule organic thin films and provide a framework to understand the experimental observations and compare them with theoretical predictions. Furthermore, I will demonstrate how by taking advantage of these modified dynamical properties, we can engineer nano-scaled glass materials with unique properties, such as higher density and resistance to thermal degradation.
Zahra Fakhraai received her B.Sc. and M.Sc. degrees in physics from Sharif University of Technology in Iran. She then joined Jamie Forrest’s group at the University of Waterloo from 2003 to 2007 to study the dynamics of polymers in thin films and on their surfaces. She received the 2007 American Physical Society’s Padden Award for her work towards her Ph.D. Zahra worked in Gilbert Walker’s group at the University of Toronto from 2008 until 2009, performing near-field infrared imaging of the structure and chemical composition of protein aggregates. Zahra received a NSERC post-doctoral fellowship in 2009 and moved to Mark Ediger’s lab at the University of Wisconsin-Madison to study properties of stable glasses until 2011, when she joined the Department of Chemistry at the University of Pennsylvania, where she is currently an Associate Professor and the Graduate Chair with a secondary appointment in the Department of Chemical and Biomolecular Engineering. Her group at Penn combines experiments and modeling to explore structure, dynamics, and optical properties of amorphous materials at nanometer length scale. Zahra is a member of the American Physical Society, American Chemical Society, Materials Research Society, and the American Association for the Advancement of Science. She is the recipient of the NSF Career award (2014), Sloan fellowship in Chemistry (2015), the Journal of Physical Chemistry JPC-PHYS lectureship award (2017), and the APS Dillon Medal (2019).