Aqueous Suspensions of Poly(ethylene Glycol)/Pyrocarbon/Fumed Silica

Adsorption of organic molecules on silica surface

“…The interaction of suspension of fumed silica and pyrocarbon silica (CS) in presence of dissolved PEG was studied using PMR spectroscopy [188]. The study showed that in the aqueous suspension of fumed silica or CS, PEG molecules are localized in the solid/liquid interface and do not form the bulk solution even at large concentration.…”

Influence of the Partial Hydrophobization of Fumed Silica by Hexamethyldisilazane on Interactions with Water

“…One can assume that a portion of the silanols remaining after silica modification by OSC in contact zones between adjacent primary particles or in narrow pores are difficult to access for OSC molecules; however, these surface patches can be easily accessible for water molecules with the size significantly smaller than that of OSC. Therefore, the 1 H NMR spectroscopy investigations show that a similar surface can disturb a relatively thick interfacial water layer (unfrozen at T < 273 K), and its thickness can exceed that of a similar layer at a hydrophilic surface. , One of the possible reasons of the observed effects is polarization of the heterogeneous surface with different charging of the hydrophobic and hydrophilic patches 13 and changes in the structure of the water layers near totally hydrophobic and hydrophilic surfaces . Besides, the nonuniform electrostatic field of the oxide surface can reorient dipoles of water molecules, which results in the enhancement of their rotational mobility and disordering of the hydrogen bond network in the interfacial water, especially near hydrophilic/hydrophobic surface patches.…”

“…Consequently, one can expect the essential dependence of the structure of the interfacial water on amounts of grafted hydrophobic TMS groups. The use of the 1 H NMR spectroscopy in combination with freezing out of bulk water and level-to-level freezing out of the interfacial water allows one to determine the thickness of the water layers disturbed differently by the surface and frozen at different temperatures, changes in the Gibbs free energy of these layers, radial dependences of interaction forces between the surface and the aqueous medium, and amounts of strongly and weakly bound waters. − …”

“…Despite published results of the investigations of the surface properties of modified silicas and the corresponding interfacial water layers, − many questions related to the relationships between the structural characteristics of modified oxides and the properties of bound water remain unclear. Therefore, the aim of this work was to study the relationships between the characteristics of the fumed silica surface partially modified by HMDS at different TMS loadings ( C TMS ) and the properties of the interfacial water layers in different media (air, liquid and frozen water, and weakly polar chloroform) at different temperatures by means of adsorption, desorption, spectroscopic, and theoretical methods.…”