PHYSICAL STRUCTURE OF POLYSILICATE PARTICLES IN ORGANIC MEDIA

Physical structure was determined for colloidal particles of a hydrophobic polysilicate sample dispersed in nonaqueous media. Some silicone products are compounded with such a material which is made by capping water-soluble silicates with organosilyl groups. Solutions densities and viscosities were measured and GPC, SAXS, and TEM were performed on the sample dispersed in THF and PDMS fluid media. Results showed that particles are relatively compact with little solvation or aggregation and have a reasonably spherical shape. The approximate ranges of particle diameter and molecular weight are, respectively, 2 to 10 nm and 2000 to 200,000 with broad, bimodal distributions. The larger particles seem to have lower densities within their hydrodynamic volumes than do the smaller ones. The average "hard-core" density is 1.17 g/cm3, similar to that of many (RSiO 3 2)x silicone resins but much less than that of amorphous fused silica. The difference is attributed to poorly packed silicate structures in the polysilicate and silicone resins. © 1991.