Dr. Sabyasachi Sen, University of California - Davis
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Abstract: A detailed understanding of the physio-chemical processes involved in the flow, structural transitions, and freezing or melting behavior of fluids confined within nanometer-sized pores of solid materials is of enormous significance in understanding a wide range of processes with applications in chemistry, biology, materials sciences, catalysis, nanofluidics, arid geochemistry. In this talk I will discuss recent spectroscopic and calorimetric results from our laboratory that provide new insights into the thermodynamic and kinetic transitions of nanoconfined fluids in their stable and metastable forms. A detailed study of the melting/freezing behavior of water confined in the highly ordered mesoporous silica confirms the core-shell model of water and provides evidence for a layer-by-layer freezing mechanism. In contrast to the freezing behavior of water, the effect of nanoconfinement on the glass transition of supercooled liquids is found to be non-universal, exemplified by the behavior of two molecular liquids, glycerol and ortho-terphenyl (OM. While glycerol shows an increase in Tg and a pronounced slowdown of the rotational dynamics due to change in the molecular packing, OTP displays a depression of Tg, with increased confinement that is influenced by the pore-liquid interface characteristics. Finally, I will present experimental evidence of the coexistence of extreme spatial and dynamical heterogeneity in both freezing and glass transition processes for these liquids confined in bimodal mesop-orous architectures with two interconnected pore types of different size and shape.
Biography: Davis Sabyasachi Sen obtained his Ph.D. in Geochemistry in 1996 from Stanford University where he was a postdoctoral fellow until 1997. He then joined the Faculty of Physics at the University of Wales in UK. From 1999 until 2004, he was a senior research scientist at Corning Incorporated. He joined the Faculty of Materials Science and Engineering at UC Davis in 2004 where he now holds the Blacutt-Undenwood Professorship. His primary research interests include the development and application of state-of-the-art spectroscopic and diffraction techniques to study atomic structure and dynamical phenomena in amorphous materials.