Reduced strength and extent of dynamic heterogeneity in a strong glass former as compared to fragile glass formers

TL;DR

This study investigates dynamic heterogeneity in a strong glass-forming liquid, revealing slower growth of correlation lengths compared to fragile glasses and identifying a temperature where heterogeneity characteristics change.

Contribution

It provides the first detailed comparison of dynamic heterogeneity between a strong and a fragile glass former using four-point correlation functions.

Findings

Dynamic correlation length grows slower in strong glass formers.

The exponent relating susceptibility and correlation length is less than 3 at low temperatures.

A change in heterogeneity behavior coincides with the onset of Stokes-Einstein violation.

Abstract

We examined dynamic heterogeneity in a model tetrahedral network glass-forming liquid. We used four-point correlation functions to extract dynamic correlation lengths xi_4^a(t) and susceptibilities chi_4^a(t) corresponding to structural relaxation on two length scales a. One length scale corresponds to structural relaxation at nearest neighbor distances and the other corresponds to relaxation of the tetrahedral structure. We find that the dynamic correlation length xi_4^{a} grows much slower with increasing relaxation time than for model fragile glass formers. We also find that chi_4^a ~ (xi_4^a)^z for a range of temperatures, but z < 3 at the lowest temperatures examined in this study. However, we do find evidence that the temperature where Stokes-Einstein violation begins marks a temperature where there is a change in the character of dynamically heterogeneous regions. Throughout the paper, we contrast the structure and dynamics of a strong glass former with that of a representative fragile glass former.