Fumed silica particles polydimethylsiloxane oligomers interface. 2. Quantum chemical modelling of particle surface. Tetragonal packing

Two model configurations of a silica supercluster have been considered usin g two identical quantum-chemical techniques, AM1 and PM3. Differences in th e technique parameters allowed to examine the impact of the straightened (A M1) and bent (PM3) configurations of the siloxane chains on the vibrational spectra of the models. Comparing the calculated spectra with the experimen tal ones, a bent configuration of the siloxane chains of the fumed silica, particles is suggested to be a reality. Quantitative characteristics of the supercluster irregularity are presented in the internal coordinates and th e reasons for the fumed silica amorphicity are discussed.