The Roughness of Aerosol Particles: Surface Fractal Dimension Measured Using Nitrogen Adsorption

Measurements were made of the surface fractal dimension of materials produced by commercial aerosol processes. A nitrogen adsorption technique was used that requires the measurement of only one adsorption isotherm, in contrast to other methods that require multiple isotherms. The materials analyzed were titanium dioxide (fumed and chloride process) and fumed silica. The chloride process titanium dioxide samples showed evidence that surface roughness is controlled by process conditions, and the fumed titanium dioxide appeared to have a surface structure that is not fractal. Results for fumed silica were compared with data from the literature that were obtained using small angle X-ray and neutron scattering. Adsorption surface fractal dimensions were lower, which is believed to be caused by the smoothing of adsorbed layers of nitrogen, resulting in the loss of replication of surface roughness.