Signal variation is due to the random Brownian motion of the particles. The light scattering is observed at a certain angle over time. In DLS analysis the sample suspension is illuminated by a laser beam, after which the laser light scatters in all directions. By measuring the random motion changes in the intensity of light scattering, DLS allows for the particle size and particle size distribution to be determined. Therefore, the distance between the scatterers in the solution is constantly changing with time. It is due to the collisions between the particles and the medium molecules. The scattered light intensity is not a constant value because the scattering intensity fluctuates over time as the result of the random movement of particles called the Brownian motion. The scattered light intensity is affected by the physical properties of the particle, such as size and molecular weight. The theory of Brownian motion states that small particles move faster than larger particles in a liquid or gas medium. Size distribution information is obtained from the Brownian motion of particles. DLS is a spectroscopy method that is used to determine the size distribution of particles in solution or suspension. Similar to electron microscopy and differential centrifugal sedimentation, dynamic light scattering is considered as a confirmatory technique following the European Commission’s guidelines on nanomaterial identification, providing direct evidence of the presence of nanoparticles and the nanoparticle size distribution.What is DLS analysis and how does it work?ĭynamic light scattering (DLS) is also called photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS). Analysis of the size distribution on the nanoparticles released into the air as airborne nanoparticles can be obtained by the EN 17199-4 small rotating drum methodology in which an electronic impactor and a nanoparticle counter are being used. The DLS particle size analysis in the liquid phase provides information on the hydrodynamic particle size of the nanoparticles. Nanoparticles down to 3 nanometers can be identified and measured. The upper limit of the technique is in the size range of approximately 10 micrometers and the strong focus of dynamic light scattering is clearly on the nanoparticle size range. The measurement range of the dynamic light scattering technique is therefore also limited on the upper range since larger particles are simply to heavy to display Brownian motion and will also settle too fast. The faster movement of the smaller particles is due to the energy transfer of liquid molecules to the solid particles and nanoparticles will experience a greater effect of this energy transfer than larger and heavier particles. The Brownian motion of particles in the liquid phase occurs randomly in every direction and smaller particles will typically travel faster than larger particles. The technique uses a laser to track the Brownian motion of particles and in particular nanoparticles. Analysis of the nanoparticle size distribution and nanoparticles identification can be obtained by means of Dynamic Light Scattering (DLS), sometimes also referred to as Photon Correlation Spectroscopy.
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