Kredentser S. Optical, magnetic and structural investigations of lyotropic suspensions with rod-like components.

The aim of this thesis is to study the liquid crystal director orientation and reorientation induced by the magnetic field in two-component aqueous suspensions of non-magnetic and magnetic rods. The magnetically induced birefringence and the reorientation of the non-magnetic component occurred due to the magnetic properties of the dilute component. The colloidal stability of an inorganic LC suspension with the addition of a magnetic component in the dispersion was studied. The stability region covers both the isotropic and nematic phases of the dispersion. The chain formation in a suspension of slightly anisotropic nanoparticles in water and in an aqueous suspension was studied. The measurements of the magnetization in fluid and frozen suspensions, and observations of the magnetic anisotropy in frozen magnetically aligned samples allowed us to confirm the existence of chains of nanoparticles in both suspensions. The single particle magneto-induced anisotropy is much smaller than many-particle (chains) anisotropy. It was established that the irradiation of an organic lyotropic suspension of absorbing pigment nanoparticles of RED176 by a laser beam with a Gaussian distribution of light intensity leads to a strong spatial redistribution of particles in the suspension. In the temperature gradient in the irradiated region, the nanoparticles were moving along the gradient and pushed out to the periphery of the beam where the spatial modulation of the particle concentration occurs. Subsequent exposure leads to the reversal of the diffusion of the nanocrystals back to the center of the laser beam. The light-induced Soret effect can be used for the recording of dynamic holograms in the isotropic phase of the colloid. The possibility of recording of stationary gratings due to the effect of light-induced adsorption of nanocrystallites onto the cell surfaces has been also demonstrated. When recording holographic gratings, the nonlinear optical coefficient had a value similar to that in a thermotropic nematic liquid crystal (so-called giant optical nonlinearity of liquid crystals).