A Study on the Correlation between Fragility and Cooperativity in Wide Class of Glass-forming Substances

The understanding of the cooperativity and heterogeneity in various kinds of glass forming liquids is a hot topic. In the present paper, the relationship between the cooperativity and the fragility has been studied based on the bond strength- coordination number fluctuation model. The model describes the temperature dependence of the viscosity of many kinds of glass forming liquids in terms of the mean values of the bond strength, coordination number and their fluctuations of the structural units that form the melt. According to the model, the cooperativity increases with the increase of fragility. The model indicates that the length scale of the cooperativity region in typical fragile systems is about 1 to 3 nm.