Ponente: Sabyasachi Sen

Procedencia: Materials Science & Engineering, University of California, Davis, CA, United States.

Abstract: 

The structure of a liquid in equilibrium undergoes rapid rearrangement with time. The structural rearrangement processes, however, drastically slow down with decreasing temperature in a glass-forming liquid as the glass transition temperature Tg is approached from above and the liquid falls out of thermodynamic equilibrium.

This kinetic slowdown is typically exemplified by the variation in the transport properties such as viscosity (or diffusivity) that can easily increase (or decrease) by ~ 15 orders of magnitude on cooling the liquid from T ~ 3*Tg to T ~ Tg. It is also at the very heart of nucleation and crystallization of a supercooled liquid and control the technological utility of glass and glass-ceramics. The dynamical processes associated with the viscous/diffusive transport have been treated in the literature principally as macroscopic phenomena within the framework of phenomenological models and often interrogated using bulk relaxation (volume, enthalpy, shear, dielectric, photon echo) experiments that typically lack a direct microscopic understanding of the atomic scale processes that accompany structural relaxation. On the other hand, the unique combination of the timescale associated with dynamical NMR spectroscopic techniques (ms to s) and the accompanying structural information, is ideally suited for probing the mechanistic aspects of the relaxational dynamics at atomic/molecular level in glasses and viscous liquids. In this talk I will present an overview of the work from our laboratory in the recent years involving the application of such spectroscopic techniques to address the nature and timescales of the various thermally driven configurational changes in a wide variety of inorganic and organic glasses and supercooled liquids and their relationship to macroscopic relaxation and transport processes.

Viernes 13 HR 

Auditorio del IF