FIBEROPTIC QUASI-ELASTIC LIGHT-SCATTERING IN CONCENTRATED DISPERSIONS- THE ONLINE PROCESS-CONTROL OF CAROTENOID MICRONIZATION

The article reviews the application of fiber-optic quasielastic light scattering (FOQELS) for the on-line and in-situ characterization of co ncentrated dispersions. In the typical configuration a single optical fiber is directly immersed in the system and is used both for illumina ting the particles by laser light and recollecting part of the scatter ed light. Specifically, when a single-mode telecommunication fiber is used, only singly scattered light is intercepted even from highly turb id dispersions. In this case the autocorrelation function of the scatt ered light can be analyzed directly in terms of the diffusion coeffici ent of the particles which is strongly related to their size. The appl ication range of the single-fiber approach in terms of concentration, particle size and dispersant viscosity is complemented by two-fiber te chniques, which, e.g., can be used to measure the light multiply scatt ered from the dispersions (fiber-optic diffusing-wave spectroscopy, FO DWS). As an example for the application of the FOQELS method, the on-l ine control of the carotenoid micronization process is described.