COATED SILICAS AND SMALL-ANGLE X-RAY-INTENSITY BEHAVIOR

Porod plots of the small-angle X-ray intensities scattered by porous s ilicas that have undergone different coating processes show deviations from the predicted constant asymptotic behaviour. The deviations are ascribed to the effect of the coating film. We propose a constant-elec tron-density model for these films. The theoretical scattering functio n calculated from the model permits an estimate of the film thickness, electron density and average number of coating molecules per unit are a of the support.