Effect of Volume Fraction and Particle Size on Depletion Flocculation of a Sterically Stabilized Latex Dispersion Induced by Addition of Poly(ethylene oxide)

Abstract

The effect of particle size, a, and volume fraction, φ s, of sterically stabilized polystyrene latex dispersions on depletion flocculation was studied using theological measurements. Three latex particles with diameters of 147, 435, and 915 nm were investigated using "free" poly(ethylene oxide) (PEO) with molecular weights of 20,000, 35,000, and 100,000. The results showed a linear relationship between the yield value τ β and (φ p - φ + p), where φ p, is the free polymer volume fraction and φ + p is the critical value at which depletion flocculation begins. This linear relationship could be represented by a scaling law with an exponent of ∼2.8 in φ s. From τ β, the energy of separation of flocs into single units was calculated using a number of assumptions. The free energy of attraction clue to depletion, G dep, was calculated using both the models of Asakura and Oosawa and of Fleer, Scheutjens, and Vincent. The latter theories show no dependence of G dep on φ s whereas E sep shows a clear increase with an increase in φ s. A scaling law could be used to illustrate the dependence of E sep on the various parameters of the system: the particle radius a, the volume fraction of the dispersion φ s, the concentration of free polymer phis; p, and the molecular weight of the free polymer.