Estimation of fractal dimension of colloidal gels in the presence of multiple scattering.

Colloidal dispersions of fluorinated polymer particles with a refractive index very close to that of water, have been used to investigate the effect of multiple scattering on the estimated fractal dimension of colloidal gels, at high-particle volume fractions. The extent of multiple scattering was varied by using cuvettes of different internal diameters, from 3 to 18 mm. Three gelation systems with different sizes and volume fractions of primary particles have been characterized by static light scattering SLS. The obtained results indicate that multiple scattering affects only the magnitude of the scattered radiation, but not the estimated fractal dimension of the gels. This result confirms the conclusion of the theoretical study reported by Chen et al. [Phys. Rev. B 37, 5232 (1988)]. As a further confirmation, the same gels have been formed in a specially designed cell, with only 0.1 mm thickness (where multiple scattering is negligible) and characterized using small-angle neutron scattering (SANS). It is found that the fractal dimension estimated from SANS measurements, without multiple scattering, is the same as that estimated from SLS measurements, in the presence of substantial multiple scattering.