Enabling the measurement of particle sizes in stirred colloidal suspensions by embedding dynamic light scattering into an automated probe head

Measuring particle sizes and size distributions in colloidal suspensions is of great importance in many technical processes. These processes are necessary for the production of polymers, pharmaceutical active ingredients and additives for the food-, cosmetic- and paint-industry. For a better process monitoring of these technical processes, online measurements of the particle size without time-consuming sampling are needed.


A novel probe head design is introduced, which enables in-line monitoring of particle sizes in undiluted stirred fluids using dynamic light scattering. The novel probe head separates a small sample volume of 0.65 ml from the bulk liquid by means of an impeller. In this sample volume, particle sizing is performed using a commercially available fiber-optical backscatter probe. While conventional light scattering measurements in stirred media fail due to the superposition of Brownian’ motion and forced convection, undistorted measurements are possible with the proposed probe head. One measurement takes approximately 30 s used for liquid exchange by rotation of the impeller and for collection of scattered light. The probe head is applied for in-line monitoring of the particle growth during microgel synthesis by precipitation polymerization in a one liter laboratory reactor. The in-line measurements are compared to off-line measurements and show a good agreement. Fulltext available at dx.doi.org/10.1016/j.measurement.2015.11.024

Authors: Martinus de Kanter, Julian Meyer-Kirschner, Jörn Viell, Alexander Mitsos, Michael Kather, Andrij Pich, Christoph Janzen.