Analysis of Light Scattered by Turbid Media in Cylindrical Geometry

摘要

The angle dependence of the transmitted light through a cylindrical turbid sample (latex suspension, developing milk gel, draining/coarsening milk, and protein foams) in a standard light scattering setup was analyzed in terms of the transport mean free path length or scattering length l~* (a measure for the turbidity) and the absorption length l_(abs). By variation of the concentration of an absorbing dye, the independence of l~* and l_(abs) was demonstrated. The resulting value of the specific extinction coefficient of the dye was found to be in fair agreement with direct spectroscopic determination and practically identical in milk and latex suspensions. The validity of this technique for obtaining l~* was demonstrated by monitoring the acid-induced gelation of milk. The possibility to simultaneously determine l~* and l_(abs) was used to follow the time development of a draining and coarsening protein foam which contained an absorbing dye. It was shown that l_(abs) can be used as a measure for the volume fraction of air in the foam. This method of monitoring the transmission of multiple light scattering provides an easy way to determine l~* and, specifically for foams, quantitative data dominated by the bulk of the foam.