Light transport and rotational diffusion in optically anisotropic colloidal suspensions

2 Magnetic and optical properties of liquid crystalline colloidal particles 33 2. Introduction This work is concerned with the solution of an important problem of influence of a magnetic field on rotational diffusion in anisotropic colloidal solutions. It describes the results of experimental investigations of the author carried out using the method of diffusing-wave spectroscopy and the method of static anisotropy in the Soft condensed matter group in the University of Konstanz within the framework of International Graduate College. The topicality of the work is defined by the barest necessity of understanding of the rotational diffusion of colloidal particles in external fields and application of this particles in new technological instruments of processing (modulation, representation) of the optical information. One of the most promising objects for this purpose are the anisotropic colloidal particles which combine the properties of anisotropic bodies and colloidal particles. Anisotropic colloidal particles consist of a nematic liquid crystalline material in crystalline phase. The combination of optical and magnetic anisotropy with the simple control of rotational diffusion provides the unique physical properties of anisotropic colloidal suspensions and defines the prospect of their use for the control of optical switching. On the other hand the magnetic field is the convenient instrument for high speed influence on the electrically neutral objects with the purpose of the modulation of their properties. The magnetic field affects the rotational Brownian motion of the anisotropic colloidal particles and changes the properties of the suspension. The diamagnetic properties of anisotropic colloidal particles cause the requirement of relatively strong magnetic fields for the noticeable change of their optical properties. That is why until the present time the properties of suspensions of anisotropic colloidal particles in magnetic fields are studied not sufficiently. Thus the investigation of insufficiently explored sides of the rotational diffusion of anisotropic colloidal particles in magnetic fields is currently a problem of vital importance. The aim of this work is establishment of the relationship between the parameters of scattering and transmission of light by the anisotropic colloidal suspension and its physical properties (concentration of the suspension, the degree of anisotropy of 5 6 CONTENTS colloidal particles, the magnitude and direction of magnetic field, the polarization of the laser beam). In conformity with the goal of this work the following problems have been posed and solved: 1. To develop the method of production of monodisperse highly anisotropic colloidal particles with high parameters of optical …