CHE Seminars  

Speaker Dr. Vijayakumar Chikkadi
Postdoctoral Scholar at ENS Lyon, France
Topic A microscopic understanding of the flow of glasses using hard sphere colloids
Date 13,November 2015 (Friday)
Place L-6 Lecture Hall Complex (LHC)
4 pm. - 5 pm.

Glasses are amorphous solids that have widespread applications due to their exceptional mechanical properties. Despite decades of research our understanding of the flow of glasses is far from complete. To develop a microscopic understanding of their deformation and flow, we need to resolve the motion of individual particles in three dimensions. Performing such experiments in atomic systems is extremely difficult. Here we have used soft glasses made of colloidal suspensions as a model system to elucidate the microscopic physics of their flow. Micron sized colloidal particles are easy to visualize and their trajectories can be followed in three dimensions using the technique of confocal microscopy.

We have constructed spatial maps of microscopic strain fluctuations in sheared colloidal glasses using the trajectories of individual particles. These maps reveal that the deformation of glasses is heterogeneous – most of the plastic strain occurs in localized regions that are often referred as shear transformation zones (STZs). The formation of a STZ, due to irreversible rearrangement of particles, gives rise to a long-range quadrupolar strain field around it. The existence of this long-range strain field is a direct evidence of the elastic nature of glasses. We have shown that elastic interaction between the STZs plays a central role in the flow of glasses, and the onset of shear banding instability.

Dr. Vijayakumar Chikkadi is mainly interested in colloidal soft matter and microscopic imaging techniques. He completed his B.E. in Mechanical Engineering from NIT Tiruchirappalli in 2001, M.S. in Engineering Mechanics from JNCASR in 2007 and PhD in soft matter at the University of Amsterdam with Peter Schall and Daniel Bonn in 2011. During his PhD the applicant developed new experimental tools to study flow of colloidal glasses, and also to visualize collective vibrations in colloidal solids. Following his PhD, he was at the Leiden University and the Weizmann Institute as a postdoctoral researcher. Currently the applicant is a CNRS postdoctoral fellow at Ecole Normale Supreieure Lyon (ENS Lyon), where he is working on colloidal active matter with Denis Bartolo.

List of Seminars