Relationship between entropic bottleneck in free energy landscape, nonexponential relaxation and fragility of glass-forming liquids

Abstract

A mesoscopic model is proposed to explain the anomalous dynamics in a supercooled liquid as its glass transition temperature is approached from above. The model is based on the assumption of β organized α process, with the requirement of coherent excitation of a minimum critical number N_c of β processes in the surroundings of a total N_β. Numerical evaluation of the model shows that the growth in this critical number in the background of a modest N_β can lead to a severe entropic bottleneck and slow down the dynamics to an extent observed near real glass transition. The fragility of the glass-forming liquid is shown to be correlated with the growth of the ratio γ(= N_c/N_β).