Prof Smarajit Karmakar

Physics of disordered systems : Dynamics and Micro-mechanics

Glasses are ubiquitous in nature, and they have wide applications. Understanding their dynamical and mechanical properties has far-reaching implications in fundamental sciences and applications. A better understanding of vitrification can help one to come up with strategies for better food and drug preservation; on the other hand, a better understanding of mechanical properties at their microscopic level can help one to design better materials for future needs. The major highlights of my research work in the last five years are the following

  • Random Pinning Susceptibility: Understanding the physics of slow dynamics of supercooled liquids near the glass transition using random pinning. This led to the proposal of a new susceptibility called “Pinning Susceptibility” to measure the growth of amorphous static order in these systems. Performed dielectric spectroscopy experiments in collaboration with TN Narayanan on supercooled Glycerol with Sorbitol and Glucose molecules as soft pinning particles to prove the method’s robustness. This paper recently got published in the Journal Proceeding of National Academy of Sciences (USA) Nexus (PNAS Nexus).

Caption: Dielectric Spectroscopy Experiments on Supercooled Glycerol to measure the growth of Static correlations in glassy liquids using Pinning Susceptibility

  • Block Analysis: Developed a new method called “Block Analysis” for finite-size scaling to study the growth of dynamic heterogeneity in glass-forming liquids. The method is superior to previous ones on two counts – one is its better-averaging properties, and the other is the inclusion of important contributions vital to dynamic heterogeneity because of its Grand Canonical ensemble-like features. It is easily extendable to experiments and other biologically relevant systems. Recently showed that the method works equally well in non-equilibrium systems like active glasses. For molecular glass experiments, we proposed a statistical analysis method using an elongated probe particle in supercooled liquids to study the growth of dynamic heterogeneity and static correlation in these systems. The novelty of the proposed method lies in looking at the dynamics with changing probe size and is easily extendable to experiments. This method is found to be equally applicable for non-equilibrium active supercooled liquids in probing the growth of dynamical heterogeneity length scale and static correlation lengths.

Caption: Schematic of Block Analysis method and Dynamics of a Probe rod in Glassy Liquids

  • Effect of Surface Relaxation in Amorphous Solids: Understanding the effects of open surface relaxation in amorphous solid samples at the nanoscale where the surface-to-volume ratio is large. Discovered the existence of an optimal aspect ratio below which the amorphous solid sample shows a neck-like failure and cavity formation above it. This will have important implications for design purposes as many parts of small devices are at length scales where the surface plays an important role in their mechanical stability. Also found an interesting method of annealing glasses using active self-propelled particles and showed that these annealed glasses have better mechanical properties but yield via shear band formation.

Caption: Cavitation in Amorphous solids and Shear band formation in Amorphous nano-pillars

  • Universal non-Debye Vibrational Density of States in Glasses: Our recent work on demonstrating the existence of a novel and universal non-Debye excess density of states (DoS) is very insightful as it shows for the first time that the DoS can have a novel power-law behaviour in amorphous solids with zero bulk shear stress, which is very different from the existing understanding. This paper recently got published in the Journal Proceeding of National Academy of Sciences (USA) Nexus (PNAS Nexus).

Caption: Excess non-Debye Modes in a Glassy Droplets to show their structural aspect

  • Active Glasses: Measured the dynamic heterogeneity and static length scales in glass-forming liquids in the presence of active non-equilibrium driving and showed that many folds enhance dynamic heterogeneity in these systems and also showed that the active glasses are inherently different from their equilibrium counterparts. This work recently got published in the journal Proceeding of National Academy of Sciences (USA) (PNAS).

Caption: Dynamic Heterogeneity gets Enormously Enhanced in Active Glass-forming Liquids and they are very different from their Equilibrium Counterparts. 

One of the major aims of my group’s research so far is to develop statistical methods and proposal of new correlation functions which can be used both in numerical simulations and in experiments equally. This outlook led to the development of some of the methods I highlighted above and below are some of the directions that we are pursuing now.

  1. Length and Time scales in Active and Passive glass Forming Liquids.
  2. Yielding of Amorphous Solids at Bulk and Nano Scale.
  3. Understanding the physics of failure mechanisms in amorphous solids at mesoscale.
  4. Origin of Ferroelectric nematic phase in a model liquid crystal system.
  5. Tuning Brittle Yielding transition in ultra-stable amorphous solids with rod-like inclusion – Micro-alloying.
  6. Anomalous Low Frequency Vibrational Modes in Amorphous solids.
  7. Active micro-rheology of soft deformable objects.
  8. Understanding Active Matter and Active Glasses within Hamiltonian Formalisms.