Photon Correlation Spectroscopy

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Photon correlation spectroscopy

Photon Correlation Spectroscopy (PCS) is a technique that is used to determine the size distribution of small particles in suspension or polymers in liquid solution. It’s also known as dynamic light scattering. It can also be used to probe the behavior of complex fluids such as concentrated polymer solutions.

When light hits small particles, the light scatters in all directions as long as the particles are small compared to the wavelength. According to the Stokes Einstein’s theory, particle Brownian motion depending on the viscosity of the suspending fluid, temperature of the fluid, diffusion coefficients of polymeric samples, molecular weights of polymers and the size of particles suspending in the fluid. Thus, the graph of scattered light can be used to determine the diffusion of particles which correlates the particle sizes.

PCS is used to characterize size of various particles including proteins, polymers, micelles, carbohydrates, and nanoparticles. If the system is mono-disperse, the mean effective diameter of the particles can be determined. This measurement depends on the size of the particle core, the size of surface structures, particle concentration, and the type of ions in the medium.
Since PCS essentially measures fluctuations in scattered light intensity due to diffusing particles, the diffusion coefficient of the particles can be determined. PCS software of commercial instruments typically displays the particle population at different diameters. If the system is mono-disperse, there should only be one population, whereas a poly-disperse system would show multiple particle populations. If there is more than one size population present in a sample then CONTIN analysis must be applied. For more than two populations CONTIN analysis at several scattering angles is required.

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