PARTICLE SIZING OF CONCENTRATED EMULSIONS USING FIBER OPTIC QUASI-ELASTIC LIGHT-SCATTERING

The recently introduced fibre optic quasi-elastic light scattering (FO QELS) technique was shown to be a fast and reproducible characterisati on method for submicron oil-in-water emulsions. The lower concentratio n limit amounted to about 1% (w/w) of dispersed phase; at lower concen trations, the reproducibility greatly decreased. Comparing the fibre o ptic modification to the classical QELS set-up, one has to take accoun t of the influence of the scattering angle, the particle concentration and the wavelength of the laser beam on the estimated value of the av erage particle size. Using a concentration series, it was demonstrated that only an apparent diameter as well as an apparent polydispersity index were obtained; owing to particle interactions and to the homodyn ing effect, both characteristics largely increased at higher particle concentrations. In order to obtain the real values, the experimentally determined data had to be extrapolated to zero concentration.