Dr. Yunlong Guo
Associate Research Scholar
Department of Chemical and Biochemical Engineering
While the physics of polymer glasses has been an active area of research for decades, the subject remains rich in a multitude of phenomena that are not fully understood. In this talk, we discuss two important themes in contemporary polymer glass science: nanoscale confinement effects on material properties and new routes to the vitreous state. Concerning the former, significant effort has been devoted to pursing an understanding of the glass transition temperature and associated dynamics of polymers confined to the nanoscale. Much of our understanding has been obtained via studies on thin polymer films. Nevertheless, studies on polymers confined to other geometries are becoming increasingly more important as we pursue questions difficult to address using thin films. We have investigated confined polymer properties utilizing nanoparticles to elucidate commonalities or fundamental differences in the deviations of glassy properties from the bulk, despite different confining geometries. Our work suggests a common origin of size effects of the glassy properties of confined polymers, irrespective of geometry, that is, interfacial effects. Furthermore, nanoparticles, as we will illustrate, offer the possibility for unique measurements at the nanoscale that would be difficult to achieve with thin films. With regards to the later theme, the general process to forming polymer glasses is by cooling from the melt. This route to the vitreous state, although known for centuries, offers limited possibility to tune glassy properties. In starting from the gas phase to make glassy materials, we are able to generate nanostructured amorphous materials formed via the assembly of molecular-scale building blocks. In comparison to the conventional glass, these nanostructured materials can have superior thermal stability (40 K enhancement in glass transition temperature), factor of 300 increase in kinetic stability as well as a 40 % reduction in density. Individually, each of these property changes is exceptional. When viewed as a whole, the combination of properties for these amorphous materials makes them truly unique.
Yunlong Guo is an Associate Research Scholar in the Department of Chemical and Biological Engineering at Princeton University. He received his Bachelor and Master Degree of Science in Automotive Engineering from Tsinghua University, and obtained his Ph.D. in Mechanical Engineering from University of Louisville in 2009. He completed an academic visit at Northwestern University in 2009 and moved to Princeton University working as a postdoctoral researcher until a promotion to his current position in 2012. His research interests include polymer glasses, nanoconfined polymer dynamics, polymer thin film and nanoparticle formation, and novel processing methods for polymers.