Структурні та адсорбційні особливості аморфного нанокремнезему, модифікованого додаванням різної кількості поліметилсилоксану

The aim of this study was to elucidate the effects of polymethylsiloxane (PMS) and pretreatment conditions on the behavior of bound water, as well the properties of the PMS/nanosilica blends. Amorphous nanosilica A-300 with addition of PMS hydrogel (PMS/A-300 weight ratio of 1:9 for dry matters) was studied in various dispersion media (air, chloroform alone and with addition of trifluoroacetic acid, TFAA) in comparison to PMS and A-300 alone and PMS/A-300 (1:1) using low-temperature 1 H NMR spectroscopy and cryoporometry. Dried nanosilica and PMS alone and in the blends were characterized using microscopy, nitrogen adsorption, infrared spectroscopy, thermogravimetry, and quantum chemistry. It was shown that the properties of the blends depend not only on the components content but also on mechanical treatment causing stronger compaction of the secondary structures of nanoparticles (aggregates of nanoparticles and agglomerates of aggregates) with increasing mechanical loading. Note that a similar behavior of various blends with hydrophobic and hydrophilic nanostructured materials was observed after hydro-compaction under different mechanical loadings. Theoretical modelling shows that the structure of bound water located at a surface of hydrophilic and hydrophobic nanoparticles changes with compaction of aggregates because of changes in the confined space effects and polarity of bound water molecules. These results reflect a general regularity appearing at appropriate amount of added water and certain mechanical loading onto the blends of hydrophilic and hydrophobic nanostructured materials, which become hydrophilic but renew the hydrophobic properties after subsequent drying.