Studies of Ordered Monodisperse Polystyrene Latexes. I. Shear Ultrasonic Measurements

Abstract

The rigidity G and the viscosity η of monodisperse polystyrene latexes were measured by the torsional quartz crystal method at 70 kHz, and an abrupt change in G and η was found at the order-disorder transition of the latexes. The torsional quartz crystal method was improved for measurements with aqueous conductive samples, and a careful calibration showed that G and η are obtained if the dielectric constant of the sample is known. In the ordered state of latex with a volume concentration of 9.3%, the apparent rigidity G and the viscosity η were about 1.5×103 dyne/cm2 and 0.6 cp, respectively, while in the disordered state G was small and η was 0.95 cp. Ordered latex is a "crystal" formed by the screened Coulomb repulsion and is a good model not only for crystals but also for ordered structures in some biological systems.