Depletion-Induced Flocculation of Concentrated Emulsions Probed by Photon Density Wave Spectroscopy

Stable, creaming-free oil in water emulsions with high volume fractions of oil (ϕ = 0.05–0.40, density matched to water) and polysorbate 80 as an emulsifier were characterized without dilution by Photon Density Wave spectroscopy measuring light absorption and scattering behavior, the latter serving as the basis for droplet size distribution analysis. The emulsion with ϕ = 0.10 was used to investigate flocculation processes induced by xanthan as a semi-flexible linear nonabsorbing polymer. Different time regimes in the development of the reduced scattering coefficient μs′ could be identified. First, a rapid, temperature-dependent change in μs′ during the depletion process was observed. Second, the further decrease of μs′ follows a power law in analogy to a spinodal demixing behavior, as described by the Cahn–Hilliard theory.