COLLOIDAL SILICA-BEARING HYDROSILANE GROUPS

Stober silica was functionalized with three silyl coupling agents: tri ethoxysilane (TES), dimethylethoxysilane (DMES, and vinyltrimethoxysil ane (VM). Microelectrophoresis, dynamic light scattering, and elementa l analysis were used to study the degree of interaction between the si lyl coupling agents and the silica surface. Small changes in the elect rophoretic mobilities and particle diameters between the unmodified (S i-OH) and DMES silica (Si-DMES) showed that Si-DMES coupled to the sur face through a single point of attachment. In contrast, the surface co upling reaction with TES (Si-TES) led to multilayered, oligomeric spec ies bound to the surface. The electrophoretic mobilities in acetone de creased from -4.47 x 10(-8) m(2) V-1 s(-1) for Si-OH to -3.87 x 10(-8) m(2) V-1 s(-1) for Si-TES and the particle diameter of Si-TES was 13 nn larger than the bare silica. Although VTM has three alkoxy groups c apable of forming large cross-linked oligomeric species, the mobility of the VTM-modified silica (Si-VTM) decreased to only -4.41 x 10(-8) m (2) V-(l) and the particle diameter increased by only 4 nm. The surfac e reaction with VTM showed that the nature of the functional group on the silyl coupling agent played an important role in determining the r eactivity of alkoxy groups with the silica surface. Using the Pt-catal yzed hydrosilation reaction, Si-TES was reacted with vinylnaphthalene (Si-TES-VN), styrene (Si-TES-ST), and vinyl-terminated poly(dimethylsi loxanes) (Si-TES-PDMS). These reactions demonstrated that Stober silic a modified with TES can lead to a variety of colloidally stable model dispersions in solvents varying in polarity from water to hexane. The modified silica systems were characterized by C-13 and Si-29 solid-sta te NMR, diffuse reflectance infrared spectroscopy (DRIFTS), elemental analysis, transmission electron microscopy, fluorescence and UV-vis ab sorption spectroscopy.