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Dynamic Light Scattering

DLS for Particle Size Analysis


When a directed laser beam shines through a liquid suspension of particles, the incoming laser light will be scattered by the particles and dispersed in all directions. The scattered light intensity can be measured under a certain angle, or under multiple angles in modern instruments.

As the particles undergo Brownian motion in their solution, the intensity of the scattered light fluctuates along with the distance between the particles. From measured fluctuation properties, more specifically from autocorrelation time, the diffusion coefficient of particles can be calculated. By knowing the solution viscosity, we can calculate mean particle size (on instruments that measure at one angle) or a particle size distribution (on multi angle instruments). This is the basis of the dynamic light scattering (DLS) technique in particle size analysis.

Application

DLS is used to measure the size of different particles in a solution, for example micelles, proteins, various polymers and nanoparticles. A big advantage of this method is the ability to measure the size of particles in their natural environment – the liquid medium. Even though very little sample preparation is required, quite reliable and fast measurements can be obtained even for very small particles (down to around 1 nm in diameter). Dynamic light scattering is one of the most often used methods for particle size analysis. However, when using DLS one should bear in mind that it works best for spherical particles in a liquid of known viscosity.

Dynamic Light Scattering
Image: Mike Jones (Creative Commons)

The Cilas Nano DS uses a combination of Static Light Scattering (SLS) and Dynamic Light Scattering (DLS).

Read more about particle size analysis.

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