ELECTROOPTICS IN DISPERSED SYSTEMS .2. REVERSING-PULSE ELECTRIC BIREFRINGENCE OF POLYSTYRENE LATEX-PARTICLES IN AQUEOUS-MEDIA

That reversing-pulse electric birefringence (RPEB) is an important tec hnique in the study of microspheres was demonstrated with two polystyr ene latexes with particle diameters of 430 and 81 nm and a styrene-gly cidyl methacrylate copolymer latex with a diameter of 48 nm. RPEB sign als were measured at 7 degrees C and at a wavelength of 633 nm in the low electric held region in the presence of and in the absence of adde d salts (Na+ or Ca2+ ions). The instrument, measurements, and analysis of RPEB signals were described in detail. Well-defined signals were o bserved for all samples that are electron-microscopically spherical an d uniform in the dry state. The particles, dispersed in aqueous media, probably form a solution phase on the outer layer of the spherical co re. The charged sulfate groups at the polymeric chain terminal behave as the polyelectrolyte in this solution phase, giving rise to the elec tro-optic effect. The sign of birefringence is either positive or nega tive, reflecting a subtle difference in the electric and optical prope rties of the solution phase. The field-off relaxation time was evaluat ed from the decay curve of the RPEB signal, and the hydrodynamic diame ters of the spherical particles were estimated. (C) 1994 Academic Pres s, Inc.