Dependent scattering effects in latex-sphere suspensions and scattering powders

The dependent scattering effects in ideal latex-sphere suspensions and beds of irregularly shaped powder grains are theoretically described by means of a coherent addition formalism together with the statistical Percus-Yevic hard sphere model for the particle separation.

Measurements are performed with a light scattering apparatus and a linear photo diode array. The latter allows scattered and directly transmitted radiation to be separated and thus the scattering cross section of the spheres in dependence of their volume fraction to be derived. For high volume fractions, a decrease of scattering efficiency occurs in the calculated as well as the measured cross sections.

For TiO₂ powders a similar behaviour of the effective scattering and absorption cross section is derived for the near- and mid-infrared region. The relevant quantities are obtained from directional-hemispherical transmission and reflection measurements using a three-flux model. Due to the irregular shape of the powder grains Mie scattering theory has to be modified for each powder to fit the experimental data.