Measurement of Particle Size and Stability of Nanoparticles in Opaque Suspensions and Emulsions with Photon Cross Correlation

PCCS is a novel technique allowing for simultaneous measurement of precise particle size and stability in the range of about 1 nm to some µm in opaque suspensions and emulsions. The key principle of PCCS is a 3D crosscorrelation technique. In a special scattering geometry, the crosscorrelation of the scattered light is calculated allowing for precise filtering of the single scattered fractions from the scattered intensity. This filtering is of decisive importance, as the well established theory for the evaluation of Photon Correlation Spectroscopy (PCS) data is only valid for light being scattered once. Any contribution of multiple scattered light to the detected signals would lead to erroneous results and misinterpretations. As a consequence, the former PCS required highly diluted suspensions in order to avoid multiple scattering. PCCS overcomes this limitation and extends the field of application to opaque suspensions and emulsions. This simplifies strongly sample preparation and handling. Clean room environments for sample preparation, as usually requested for the well established PCS, is no longer necessary. This broadens the field of applications, and many samples can be investigated even in the original state without dilution, now. As an additional benefit, the stability of the sample can be investigated simultaneously, showing if the sample is in a stable state or a sedimentation, growth, or flocculation process is taking place. Basing on this 3D cross correlation technique, a novel instrument has been developed and optimized for industrial use. Housed in a small table top unit it contains all necessary parts such as light source, detectors, the correlator and the sample containing vial and is ready four routine measurements in any laboratory. The operation is much simpler than with a conventional PCS system, because the samples are not diluted or at the utmost diluted moderately. Costly cleaning and sample preparation effort is avoided.