PARTICLE CHARACTERIZATION BY AC-ELECTROKINETIC PHENOMENA - 3 - NEW DEVELOPMENTS IN ELECTROROTATIONAL LIGHT-SCATTERING (ERLS)

Dielectric dispersions of the polarizability of suspended particles ca n be directly measured by electrorotation (ER). The method records par ticle rotation spectra in rotating electric fields of the radio freque ncy range. The frequency dependence of ER spectra is characterized by individual rotation peaks which provide information on inherent electr ic particle structures. To avoid the inconveniences of microscopic reg istration of particle rotation we developed electrorotational light sc attering (ERLS). Results on human red blood cells, platelets and condu cting latices are presented. For all particles the obtained ERLS spect ra corresponded to microscopic measurements. New methodological develo pments such as the introduction of optical microstructured chambers ar e discussed. These chambers possess a simple structure and expand the available frequency and conductivity range. A special measuring proced ure which distinguishes between the rotation sense at the measuring fr equency relative to the sense at a reference frequency is presented. T he procedure is also useful to reject the contributions of held-induce d particle motions other than ER and to enhance the sensitivity of ERL S in frequency ranges of smaller particle rotations. (C) 1998 Elsevier Science B.V.