Department of Physics

Indian Institute Of Technology Madras , Chennai

What are glasses?

Speaker : Prof. S.S.N. Murthy, Jawaharlal Nehru University, Delhi

2015-12-08

Abstract :

The word "glass" is generally used for kinetic freezing of translation degrees of freedom where the viscosity reaches to about 1013 poise on cooling. Associated with this increase in viscosity is a relaxation process (the main alpha-process), and a step – like transition in CP data at the glass transition temperature Tg. However, this word "glass" has to be redefined as glass like transitions are observed in orientational disordered phase as in glassy crystals and to the kinetic freezing of translational motions as in supercooled liquid crystals. All these definitions allow these groups of substances to be classified as glasses which reveal the so called main process that is non–Arrhenius and non–Debye in relaxation characteristics. In addition, glassy state is not a completely dead state. Some weak relaxation process occur below the glass transition temperature which are vital to the understanding the glasses. Although, it is tempting to attribute to the dynamic heterogeneity to spatial heterogeneity, the observations of similar feature in disordered glassy crystals raises questions about the spatial heterogeneity models.

Glasses can be classified strong or fragile depending upon their deviation from Arrhenius behavior. In the context of the observation of near Debye like alpha - process as in hexa-substituted benzenes indicates that this group may be classified as strong glasses with secondary process located close to the main process. The time scale problem is not unique to glasses. These are observed in ices of water in hexagonal lattice, and also in the cubic structure of clathrate hydrates. It is doubtful whether these systems can be classified as glasses as reorientational motion of water molecules is strongly accelerated on addition of very small quantity of hydroxides like KOH, NaOH. Here in this talk broad band dielectric spectroscopic results and calorimetric data are shown.

ABOUT THE SPEAKER:

Prof. S.S.N. Murthy is an experimental condensed matter physicist working at Jawaharlal Nehru University (JNU). Prof. Murthy is an alumni of IIT Madras, Dept. of Physics, where he completed his PhD in 1985. He then moved to IISc for postdoctoral work before taking up a faculty position at JNU. He has been a full professor at JNU since 2004, has guided five PhDs and authored nearly 60 publications, which have garnered ~1300 citations. He is a sought after speaker internationally and has been a visiting professor at the Donostia International Physics Centre, Sans Sebastian, Spain.

Key Speaker Prof. S.S.N. Murthy, Jawaharlal Nehru University, Delhi
Guests None
Place Seminar Room
Start Time 5:00 PM
Finish Time 6:00 PM
External Link https://physics.iitm.ac.in/colloquium/ssn_murthy_aug15.pdf