Particle Sizing using DWS


Besides the measurement of the microrheological properties of a sample, Diffusing Wave Spectroscopy (DWS) can also accurately determine the mean diameter of particles in dispersions. In particular, this clever approach enables particle sizing in samples with turbidity exceeding the turbidity limit accessible by the most sophisticated Dynamic Light Scattering (DLS) technologies. 


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Image depicts the newest version of DWS RheoLab.

DWS Rheolab


Since DWS is a fast and non-invasive technique, it has significant advantages over traditional particle sizing techniques which require sample preparation (scanning or transmission electron microscopy) and allows in situ studies of time dependent phenomena like aggregation kinetics.


The DWS RheoLab from LS Instruments is the only instrument which offers this novel light scattering technology for particle sizing. In particular, the DWS RheoLab performs accurate and reliable measurements in a matter of minutes over a broad range of sizes, concentrations and materials.


DWS can be used to perform particle sizing from 100 nm to 1 micron. For monodisperse particles of particles with a gaussian size distribution, the accuracy is better than 5%.


A - Accuracy of DWS sizing measurements as a function of turbidity, characterized by the inverse of the transport mean free path, l*. Measurements were carried out on aqueous suspensions of spherical polystyrene particles with radii of  (\(\blacksquare\)) 111nm, (\(\bullet\)) 220nm, (\(\blacktriangle\)) 280nm, (\(\blacktriangledown\)) 385nm, and

(\(\blacklozenge\)) 960nm, and on melamine particles with radii of (\( \square\)) 296nm, and (\(\circ\))516nm, at different mass fractions (indicated by the colored numbers in the bottom right-hand corner). Within the size range [100nm, 1μm] and the turbidity range shown, an accuracy of ± 5% is achieved.


B – Examples of inappropriate (left) and appropriate (right) samples for DWS sizing measurements. However, we note that the left sample can be measured using Modulated 3D Cross-Correlation DLS, whereas the right sample cannot.