Electro-optics in Dispersed Systems

That reversing-pulse electric birefringence (RPEB) is an important technique in the study of microspheres was demonstrated with two polystyrene latexes with particle diameters of 430 and 81 nm and a styrene-glycidyl methacrylate copolymer latex with a diameter of 48 nm. RPEB signals were measured at 7°C and at a wavelength of 633 nm in the low electric field region in the presence of and in the absence of added salts (Na + or Ca 2+ ions). The instrument, measurements, and analysis of RPEB signals were described in detail. Well-defined signals were observed for all samples that are electron-microscopically spherical and uniform in the dry state. The particles, dispersed in aqueous media, probably form a solution phase on the outer layer of the spherical core. The charged sulfate groups at the polymeric chain terminal behave as the polyelectrolyte in this solution phase, giving rise to the electro-optic effect. The sign of birefringence is either positive or negative, reflecting a subtle difference in the electric and optical properties of the solution phase. The field-off relaxation time was evaluated from the decay curve of the RPEB signal, and the hydrodynamic diameters of the spherical particles were estimated.