Dynamics of Glass Forming Liquids with Randomly Pinned Particles.

Saurish Chakrabarty,Chandan Dasgupta,Smarajit Karmakar

doi:10.1038/srep12577

Abstract

It is frequently assumed that in the limit of vanishing cooling rate, the glass transition phenomenon becomes a thermodynamic transition at a temperature TK. However, with any finite cooling rate, the system falls out of equilibrium at temperatures near Tg(>TK), implying that the very existence of the putative thermodynamic phase transition at TK can be questioned. Recent studies of systems with randomly pinned particles have hinted that the thermodynamic glass transition may be observed for liquids with randomly pinned particles. This expectation is based on the results of approximate calculations that suggest that the thermodynamic glass transition temperature increases with increasing concentration of pinned particles and it may be possible to equilibrate the system at temperatures near the increased transition temperature. We test the validity of this prediction through extensive molecular dynamics simulations of two model glass-forming liquids in the presence of random pinning. We find that extrapolated thermodynamic transition temperature TK does not show any sign of increasing with increasing pinning concentration. The main effect of pinning is found to be a rapid decrease in the kinetic fragility of the system with increasing pin concentration. Implications of these observations for current theories of the glass transition are discussed.

Highlights

It is frequently assumed that in the limit of vanishing cooling rate, the glass transition phenomenon becomes a thermodynamic transition at a temperature TK
Using standard methods to analyze the observed temperature dependence of the structural relaxation time τα, we find that the Mode Coupling Theory (MCT) temperature tical temperature (TC) increases and the VFT-divergence temperature TVFT remains nearly constant or decreases slowly with increasing pin concentration
The observed dependence of TC on ρpin is consistent with the prediction of Ref. 17, but the dependence of TVFT on ρpin is in disagreement with the theoretical prediction of Ref. 17 and the numerical results reported in Refs 24 and 35 if we assume that a thermodynamic transition at which the configurational entropy density sc goes to zero coincides with a divergence of τα

Summary

OPEN Dynamics of Glass Forming Liquids with Randomly Pinned Particles

Saurish Chakrabarty[1], Smarajit Karmakar2 & Chandan Dasgupta[1,3] received: 16 April 2015 accepted: 26 June 2015 Published: 24 July 2015. Recent progress[5,6,7,8,9,10,11,12,13,14,15,16] in understanding various dynamical aspects of this phenomenon has shed some light on this subject, but the question of whether an “ideal” thermodynamic glass transition, signaled by the vanishing of the configurational entropy density, can occur at a temperature lower than the experimentally defined (dynamic) glass transition temperature remains unanswered It was proposed in Ref. 17, that the difficulty in observing the putative ideal glass transition in simulations and experiments can be bypassed by considering liquids in the presence of quenched disorder and studying the effects of varying disorder strength on the thermodynamic and dynamic properties of the liquid. We have carried out a detailed study of the dynamics for two model glass forming liquids in the presence of random pinning using extensive numerical simulations

Theoretical predictions

Systems and Methods

Results

As shown in

Conclusion

Additional Information