Statistical model of synchronized cooperative motion in glass-forming liquids

This paper presents a theoretical framework describing the tendency for synchronized positional rearrangements of any two structural species in a multicomponent glass-forming liquid. Such correlated motions are especially important as the glass-forming liquid approaches the glass transition. It is established that the expected cage-breaking probability of a structural unit is proportional to the dynamical propensity of the structural unit calculated via the isoconfigurational ensemble method. This theoretical framework supports the notion that spatial heterogeneities in composition result in dynamical heterogeneities, enabled by synchronized positional rearrangements. Using this model, an alkali borosilicate glass is investigated as an example, and results indicate that structural species with large differences in enthalpy might inhibit the expansion of cooperative rearranging regions and increase the number of such regions. The physical impact on relaxation time distribution and configurational entropy are also discussed.