Fumed silica particles/polydimethylsiloxane oligomers interface. I. Quantum-chemical modelling of particle surface. Cubic packing

The paper opens a series of publications devoted to a microscopic approach to the intermolecular interaction between fumed silica particles and polydimethylsiloxanes of different structure. The paper presents results on atomic characterization of the surface of both hydroxylated and silylated particles in a supercluster approach. A rhomb-like-four-layer supercluster containing 222 atoms is proposed as the basic unit simulating an individual surface facet of the hydroxylated silica particle with a (111)-like packing of the siloxane elements. The total-energy-minimization procedure for obtaining equilibrated cluster structures has been performed at the level of semiempirical quantum-chemical considerations by using the AM1 method. The optimized basic cluster served as a basis for a microscopic examination of the silylation process. The supercluster characteristics are presented by distribution functions related to atomic charges, bond lengths, and bond angles.