The effect of the size of particles on optical and electrooptical properties of colloids

We have considered optical and electrooptical properties of disperse systems that contain particles with different optical characteristics, sizes, and shapes. Our investigations of the refractive index of a series of disperse systems have shown that, if the particle size does not exceed a few tens of nanometers, the refractive index does not depend on the particle concentration and is equal to the refractive index of a molecular medium that surrounds particles. We have shown that, in an external electric field, systems with these particles almost do not possess birefringence but possess dichroism. Our investigations of systems with a low concentration of particles allowed us to find that the intensity of light transmitted through a Kerr cell that is filled with colloidal particles with a size comparable with the wavelength and that is placed between crossed polarizers varies proportionally to the squared dichroism induced in the colloid by the external field. Linearly polarized light transmitted through this cell in the electric field remains to be linearly polarized, but its plane of polarization rotates by an angle the tangent of which is proportional to the dichroism of the colloid. We propose a method for determining the contributions from birefringence and dichroism to the observed electrooptical effects.