Dynamic Light Scattering
- Particles suspended in a liquid are subject to Brownian motion.
- Small particles diffuse“faster”.
- Large particles diffuse “slower”.
- The time variation of the scattered intensity is analyzed by examining their auto-correlation. From this a diffusion coefficient can be derived. Please see our literature section for additional infornmation.
- 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.
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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.
- Available algorithms can be used to extract “true” size distributions from complex samples - NNLS, CONTIN.
Two instruments which use this principle to determine particle size are our 90Plus bench top and our BI-200SM goniometer units.
Estimates of Protein Molecular Size and Polydispersity can be obtained using this method.