LINEAR VISCOELASTIC PROPERTIES OF ORDERED LATICES

The frequency-dependent behavior of the storage modulus G' and loss mo dulus G '' has been measured for an ordered latex at different volume fractions. From these measurements the volume fraction dependency of t he static shear modulus was obtained. The theoretical static shear mod ulus has been deduced from a stress tensor expression which only takes into account the electrostatic pair interactions between nearest neig hbors. The electrostatic pair interaction is modeled adequately to acc ount for the multiparticle environment of a particle and for high surf ace charges. The interactions are described by the linear superpositio n approximation for the pair interaction energy between two particles given by Bell et al. [J. Colloid interface Sci. 33, 335 (1970)]. The a pparent surface potential and the effective Debije screening length us ed in this expression are determined from the electrostatic potential which is numerically determined from the Poisson-Boltzmann equation in a spherical cell. The theoretical model is also compared with measure ments of several other investigators. Most of the experimental data ca n be scaled to a single mastercurve resulting from the proposed theore tical model. (C) 1995 Society of Rheology.