Small-angle X-ray scattering of silica dispersions at low particle concentrations

Abstract

Small-angle X-ray scattering was used to determine the particle size distribution of a colloidal silica suspension. Four methods of data analysis, all corresponding to different moments of the particle size distribution, were chosen. The values thus found for the average particle size were consistent and in good agreement with the particle size distribution which was also determined. The maximum of the distribution was at a radius of 18 nm and the standard deviation was 4 nm. This fitted very well with the size distribution obtained with electron microscopy. The particle interactions were also studied with small-angle X-ray scattering. It was found that the interaction could be described by a hard sphere potential if a specific hard sphere volume of 0.64 ± 0.09 cm 3 g −1 was assumed. This corresponds well with the reciprocal mass density which was found to be 0.58 ± 0.01 cm 3 g −. Static and dynamic light scattering and sedimentation experiments confirmed these results. From the molar mass which was also determined with SAXS, M = (4.7 ± 0.9) · 10 7 g mole −1, and from the specific hard sphere volume, the hard sphere diameter was calculated to be 45.6 ± 3.6 nm. The hard sphere diameter found from the concentration dependence of the radius of gyration was 12.6 nm, which is unrealistically low compared with the particle radius. A qualitative explanation has been found.