DYNAMIC LIGHT-SCATTERING FROM ORIENTED, ROTATING PARTICLES - A THEORETICAL-STUDY AND COMPARISON TO ELECTROROTATION DATA

In recent years, electrorotation has developed in the held of biology as a technique for characterization of single cell dielectric properti es. Applications to colloidal particles are scarce, although the metho d provides information on the electrical structure of the particle's i nterior. The method explores the frequency-dependent polarizability di fference of the particles and the suspension medium by using rotating fields in the frequency range of 1 kHz to 200 MHz to induce individual particle rotation. To allow interpretation of the electrorotation spe ctra measured with light scattering techniques, the theoretical autoco rrelation function of light scattered from rotating particles of cylin drical symmetry has been calculated. All particles were assumed to pos sess a single scattering site and the rotation axes were assumed to be parallel. An appropriate expression for the rotational diffusion arou nd the longitudinal angle was also derived. Diffusion around the azimu thal angle could be neglected. The theoretical result consists of a we ll structured autocorrelation function. The theoretical limits of part icle size and rotation speed that allow detection of electrorotation w ere explored. Experimental autocorrelation functions from electrorotat ion of human red blood cells could be explained theoretically when rea sonable parameters for the cells' properties were assumed.