Relationship between Entropic Bottleneck in Free Energy Landscape, Nonexponential Relaxation and Fragility of Glass-Forming Liquids

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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 Nc of β processes in the surroundings of a total Nβ. Numerical evaluation of the model shows that the growth in this critical number in the background of a modest Nβ 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(= Nc/Nβ).