Structure and dynamics of suspensions of charged rod-like particles

Suspensions of charged rod-like particles are investigated theoretically in a concentration regime where the mean distance between rods is comparable to their length, L. The structure of these systems is studied by Monte Carlo simulations and a perturbation theoretical scheme. Results for the pair distribution function g(12) are obtained, which show the onset of angular correlations at the cross-over concentration c*=L–3. Above c* there is a tendency for local alignments of neighbouring rods, although the systems remain globally isotropic up to c= 4c*, which is the highest concentration investigated. As a consequence, the peak position kmax of the structure factor S(k) scales as kmax∼c1/2 for c > c* in contrast to the c1/3 behaviour for c < c*, where the rods behave as spherical particles. The time-correlation function of quasielastic scattering experiments is derived from a dynamical mean field theory. From it the collective diffusion coefficient and the first cumulant are obtained. The influence of the interaction between rods and of the coupling of translational and rotational diffusion are discussed.