Application of a new light scattering technique to avoid the influence of dilution in light scattering experiments with milk

Colloidal systems are a subject of great interest in soft condensed matter research as well as in industry. But the ability to characterize colloidal systems with dynamic light scattering (DLS) is in general limited to systems with negligible contributions from multiple scattering of light. Therefore a variety of systems is excluded from investigations with DLS at high concentration and therefore increased turbidity. Often these samples were investigated under high dilution with, at least for some systems, a high probability of measuring artefacts. A promising solution to this problem consists of suppressing multiple scattering in a DLS experiment with a cross-correlation technique. Therefore we developed a so-called 3d cross-correlation instrument which enables us to characterize extremely turbid suspensions. After having found that the instrument works very well with model systems, we now demonstrate that complex ‘real world’ systems can successfully be characterized using this technique. An investigation of milk shows a strong dependence of the measured particle size distribution upon dilution. With the 3d instrument, however, the undiluted milk can be measured and artificial changes of the sample properties can be excluded.