Dynamic Light Scattering
Particles suspended in a liquid are subject to Brownian motion
Small particles diffuse“faster”
Large particles diffuse “slower”
From the measured diffusion coefficient particle size is calculated
A beam of laser light is focussed in the sample
Particles in the scattering volume scatter light in all directions
The scattered photons are measured by a photomultiplier tube
The Intensity appears to fluctuate randomly
A digital correlator is used to compute the autocorrelation function
The autocorrelation function is an exponential decay:
Each monodisperse population of particle sizes produces its own unique autocorrelation function - a single exponential decay
Mixtures of more than one size population produce sums of exponentials
Commercially available algorithms can be used to extract “true” size distributions from complex samples - NNLS, CONTIN.
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