Restructuring of Soot Fractals in Flames: Small-Angle X-ray and Light Scattering Experiments

This lecture proposes the comparative analysis of Polarized Laser Light Scattering (PLLS) and small angle X-ray scattering (SAXS) experimental studies performed on diffusion flame systems. The wavelengths of the two kinds of electromagnetic radiation differ of about 4 order of magnitudes (lambda=514.5 nm for PLLS and lambda=0.077 nm for SAXS at 16 keV energy in this work). The complimentary character of the two techniques is evident if one observes that the phase shift on the minimum observable particle lighted by the incident electromagnetic radiation must be detectable. A standard rule-of-thumb fixes at about lambda/10 the minimum size of particles for which scattering techniques can be applied. This rough experimental criterion justifies the fact that a particle smaller than 20 nm very hardly will be detected by laser light. Vice versa, SAXS has an ideal down-size limit of a few Ångströms, and allows for detecting of very small particles and molecular clusters (di Stasio, 2001a; di Stasio et al, 2006).