Structural anisotropy of fractal aggregates and its exhibition in electrooptical effects

The first experimental examination of orientational turbidimetric effect [d ifferential orientational spectrum of optical density deltaD(lambda) in sus pensions of fractal clusters was presented. Experiments were performed for aqueous suspensions of powdered Aerosil OX-50 aggregates ordered by the alt ernating electric field oriented along or across the unpolarized light beam . Experimental differential spectra deltaD(lambda) are essentially differen t from the known spectra for bacterial and yeast suspensions. In particular , the points of zero effect lie in the red (but not in the blue) region of spectrum, and the \deltaD(lambda)\ dependence is a decreasing function in t he range 300-800 nm. To explain these results, a theory was developed based on the three-dimensional lattice model of cluster-cluster aggregation and the optical model of interacting dipoles. This theory confirms main conclus ions obtained previously in the Rayleigh-Debye-Hans approximation (Khlebtso v, N.G. and Mel'nikov, A.G., Kolloidn. Zh., 1998, vol. 60, no. 6, p. 843) a nd agrees with experimental deltaD(lambda) spectra. It was shown experiment ally and theoretically that the structural anisotropy of aggregates exhibit ed scale invariance, and the differential spectra for the aggregates with v arious numbers of particles are described by a single universal curve delta D(kR(g)), where k = 2 pi/lambda and R-g is the mean radius of gyration of a ggregates.