S. Di Stasio, Feasibility of an optical experimental method for the sizing of primary spherules in sub-micron agglomerates by polarized light scattering, APP PHYS B, 70(4), 2000, pp. 635-643
The possibility of inferring by a non-invasive experimental method the size
of primary particles (spherules), which constitute the agglomerated soot g
enerated in an ethylene-air diffusion flame, is investigated. In contrast t
o the predictions from the Mie theory for isolated spheres, experimental ev
idence is provided here about the fact that the size of spherules (some ten
s of nanometers), which stick together to form agglomerates (some hundreds
of nanometers), can be recognized from polarization ratio measurements. Val
idation of the proposed scattering technique is obtained by first performin
g standard measurements of the primary particle size by SEM analysis of soo
t samples taken on quartz inserted directly in the flame along the burner a
xis. Then, the polarization ratio P(theta) = sigma(HH)/sigma(VV) of scatter
ed light is measured at the same locations and for the same flame condition
s for different polar scattering angles theta. As major result, evidence is
provided of a linear relationship existing between the primary sizes, obta
ined independently by SEM analysis, and the measurements of the polarizatio
n ratio P(90 degrees). Finally, a procedure is reported and applied to retr
ieve the absolute spherule size from the direct observation of the transiti
on between the power-law and Pored's scattering regimes, which correspond t
o the domains of long-range (fractal) and short-range (not fractal) interac
tions between primary particles, respectively.