Particle characterization by AC-electrokinetic phenomena 3. New developments in electrorotational light scattering (ERLS)

Abstract

Dielectric dispersions of the polarizability of suspended particles can be directly measured by electrorotation (ER). The method records particle rotation spectra in rotating electric fields of the radio frequency range. The frequency dependence of ER spectra is characterized by individual rotation peaks which provide information on inherent electric particle structures. To avoid the inconveniences of microscopic registration of particle rotation we developed electrorotational light scattering (ERLS). Results on human red blood cells, platelets and conducting latices are presented. For all particles the obtained ERLS spectra corresponded to microscopic measurements. New methodological developments such as the introduction of optical microstructured chambers are discussed. These chambers possess a simple structure and expand the available frequency and conductivity range. A special measuring procedure which distinguishes between the rotation sense at the measuring frequency relative to the sense at a reference frequency is presented. The procedure is also useful to reject the contributions of field-induced particle motions other than ER and to enhance the sensitivity of ERLS in frequency ranges of smaller particle rotations.