![]() ![]() The amplitude of the cross-correlation function, which depends on the proportion of multiple scattering, enables direct measurement of changes in particle number and particle size. Therefore, a single scattering signal is sufficient to start the particle size analysis. The single scattered light is thus separated from the multiple scattered light. By the cross correlation of both signals the single scattered light, used for the correct calculation of the particle size distribtion, is filtered out from the multiple scattered light part. PCCS acquires two separately induced scattered light intensities. The PCCS technology will help to eliminate the influence of multiple scattered light in principle. However, this conventional technology requires extremely diluted samples in order to deliver meaningful results. The principle of dynamic light scattering traditionally is realised with Photon Correlation Spectroscopy (PCS) which uses auto-correlation of scattered light intensities in order to determine particle size distribution. Unwanted sample dilution can be avoided and particle size measurements in the original concentration of the respective application are possible. The application of cross-correlation significantly enhances the concentration range for samples which can be measured with dynamic light scattering. PCCS opens possibilities for analysis of nanoparticles in suspensions and emulsions with hundreds of times higher solids concentrations than before. The particle size distribution can be calculated with the correlation function, which follows an exponential decay. The scattered signal is correlated with itself at different points in time (a comparison of the time lagged and the original function). With the help of a photodetector the scattered light intensity is monitored over time and then autocorrelated. Thus the intensity of the entire scattering wave fluctuates between a minimum (destructive interference) and a maximum value (constructive interference) over time. The random motion (Brownian motion) of the particles changes the distance to each other and therefore the spatial superposition (interference) of the individual scattering waves. ![]() Due to optical interference of all partial waves an overall scattered wave is generated. The particles interact with the laser light and generate single scattering waves. The principle of DLS traditionally is realised with Photon Correlation Spectroscopy (PCS) where one laser beam is transmitted through the sample. ![]()
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