Molecular dynamics simulations of monofunctionalized polyhedral oligomeric silsesquioxane C6H13(H7Si8O12)

Polyhedral oligomeric silsesquioxanes (POSS), functionalized witha single hexyl substituent, have been studied using molecular dynamics (MD) simulations based on a reactive interaction potential. This potential is designed for mixed covalent-ionic interactions and facilitates the charge transfer that is associated with the rupture and formation of covalent bonds. The potential has been optimized to reproduce the known structural characteristics and dynamic properties of POSS. The model was then employed to study the melting behavior of crystalline monohexyl-POSS as well as the structural reorganization during subsequent cooling and glass formation. Simulations predict a melting temperature of crystalline monohexyl-POSS of 430 K. The amphiphilic nature of the structural building block in this compound is evident in the crystal phase through preferred POSS-POSS and hydrocarbon-hydrocarbon groupings, which give rise to a bilayered structure. Melting seems to originate from within the organic layers. A preference for groupings of like species is also apparent in the glass.