Sabyasachi Sen

Sabyasachi Sen obtained his Ph.D. 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, where he was until 1998. From 1999 until 2004, he was a senior scientist in the glass research group at Corning Incorporated. He joined the Faculty of Materials Science and Engineering at UC Davis in 2004, where he served as the vice-Chair and now holds the Blacutt-Underwood Professorship.  His research interests include the development and application of state-of-the-art spectroscopic, diffraction and rheological techniques to study atomic structure and dynamical phenomena in amorphous and crystalline matter.  He has authored/co-authored 240 scientific papers on glasses and ceramics and is the recipient of several awards in glass science.

Title:  Viscoelastic behavior of molecular vs. network glass-formers: Are they fundamentally different?

Abstract:  The viscoelastic behavior of a wide range of inorganic and organic glass-forming liquids are investigated using rheological measurements in the linear regime.  While the behavior of the network liquids is observed to follow the classical Maxwell model of spring-dashpot combination with a relatively narrow distribution of relaxation times, the molecular liquids display a strong departure from this behavior.  Besides a violation of Maxwell scaling in the terminal regime, a purely viscous response and a Newtonian regime are not recovered for these molecular liquids, even at the lowest frequencies of measurement.  Direct dynamical measurements using NMR and X-ray Photon Correlation spectroscopic techniques indicate that these liquids are characterized by a rather broad distribution of relaxation times.  We propose that their rheological behavior is better described by the fractional Maxwell model with “springpot” elements replacing the conventional spring-dashpot combination.