Order/disorder transitions in concentrated electrocratic dispersions

Abstract

The order/disorder phase transition in concentrated polymer latex dispersions in discussed in terms of the packing of “effective spheres” consisting of the latex particle surrounded by its electrical double layer, which adds an amount λ/κ to the particle radius. For the systems considered here, of 85 nm radius polystyrene particles in KCl, λ is approximately 1.9. The dependence of the Debye screening length 1/κ on particle concentration is examined in an Appendix: the effect is relatively small. If the onset of ordering of the spheres is supposed to commence when the volume fraction of “effective spheres” reaches 0.50, and ordering is complete at a volume fraction of 0.74, then the experimentally observed phase diagram is well reproduced. The effect of particle size on the phase diagram is predicted.