Backscattering DLS is used to characterize inks
Inkjet inks are nanoparticle dispersions which can be characterized by Dynamic Light Scattering (DLS) . Inkjet inks are usually formulated at much higher concentrations than can be normally analyzed with Dynamic Light Scattering DLS without dilution. It is possible to analyze inkjet inks at higher concentrations when the analysis is performed in a way that negates the influence of multi-scattering effects. By focusing the laser beam just inside the cuvette and positioning the detector to receive the back-scattered light that comes out, one can perform DLS measurements on high concentration dispersion. The Nicomp N3000 is unique because with the mini-goniometer it can perform measurements at 90 degrees and at 170 degrees. A special cuvette holder is used to move the cuvette so that the focal point of the laser can be optimized for each type of measurement.
No other DLS instrument can offer this capability.
Figure A has the PSD from an aqueous ink diluted by a factor of 500 and at 90 degrees. This would represent a classic DLS measurement. There is a peak at 30 nm, assigned as the primary particle size and another peak at nearly 100 nm, probably aggregates. Figure B contains the same ink, undiluted, in backscattering mode.