Structural relaxation time and rigidity of deionized suspensions of monodisperse polystyrene latex spheres

Abstract

Structural relaxation time (τ) of ordered structures is observed for the first time by the spectrophotometric and conductance stopped-flow techniques for deionized polystyrene latex spheres (35–500 nm in diameter), for which the distributions are both ‘‘crystal-like’’ and ‘‘liquid-like.’’ Two kinds of τ values, fast (τf) and slow steps, are observed. The τf values decrease with latex concentration. Theoretical values for τf, calculated using the translational diffusion constants of the latex spheres evaluated by the Einstein–Stokes equation, agree very well with the observed τf values for the strongly interacting colloids. The results support the hypothesis that electrostatic intersphere repulsion is essential to explain the dynamic properties of the spheres. The effective diameter of the spheres must include the Debye-screening length. The rigidity of the deionized and crystal-like latex suspension, which is estimated from the τf values, ranges from 0.005 to 10 dyn cm−2, and increases as the concentration and the charge density of the spheres increase and/or the size decreases.