Influence of ultrasonic vibration on the mesoporosity and surface fractal dimensions of resultant silica xerogels

The present work has investigated the influence of ultrasonic vibration during sol preparation on the mesoporosity and surface fractal dimensions of resultant silica xerogels, in comparison with magnetic stirrings. The xerogels are derived from hydrochloric acid-catalyzed TEOS (tetraethyl orthosilicate) systems (acetone as solvent). The sols were agitated under ultrasonic vibration (of high or low intensity) or by magnetic stirring in sealed containers for 30 minutes, and then gelled in the air with solvent evaporation. The resultant wet gels were dried in ambient conditions after 11 days of aging or not, and became xerogels. Image analyses based on the FE-SEM (field emission gun-scanning electron microscopy) images of these xerogels showed that high intensity of ultrasonic vibration caused a distinct mesoporosity decrease of the resultant xerogels, and that despite the different ultrasonic intensities, samples prepared under ultrasonic vibrations showed similar surface fractal dimensions which were different from those of classic samples. The influence of aging is also presented.