Analysis of the nanoparticle size distribution and nanoparticles identification can be obtained by means of Dynamic Light Scattering (DLS). The technique uses a laser to track the Brownian motion of particles and in particular nanoparticles. 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 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 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 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. Nanoparticles down to 3 nanometers can be identified and measured, the lower limit also depends somewhat on the particle density.
Nanoparticle size DLS equipment and analysis conditions
The DLS particle size analysis is always executed in the liquid phase, also for dry powders and provides information on the hydrodynamic particle size of the nanoparticles. The nanoparticle size analysis can be executed in water but also in other liquids in order to avoid disssolution of the particles. We have several types of equipment in our laboratory such as the Coulter N4 and also the Malvern Zetasizer Nano ZS. The latter cannot only measure the size distribution of nanoparticles but it also is capable of measuring the Zeta potential. Analysis of the Zeta potential is critical in assessing the stability of the nano particle dispersion and can prevent or promote nanoparticle agglomeration.
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 on the presence of nanoparticles and information on the nanoparticle size distribution.
Nanoparticle size measurement in air
Analysis of the size distribution of 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 as detectors for information on not only the size of the nanoparticles but also the number of nanoparticles. We have a separate page on this methodology that we have developed in house.
Dynamic Light Scattering FAQs
Dynamic light scattering, or DLS, is a technique used to measure the size distribution of particles dispersed in a liquid. A laser detects fluctuations in the light scattered by particles undergoing Brownian motion, and this information is used to calculate their hydrodynamic particle size.
DLS measures the hydrodynamic diameter of particles in suspension. This represents how the particles move through the liquid and can include the influence of particle shape, surface coatings, solvation layers and agglomeration.
The exact measurement range depends on the material, concentration and measurement conditions. DLS is primarily used for particles in the nanoscale range and can measure nanoparticles down to approximately 3 nanometres. The upper limit is approximately 10 micrometres, although the technique is most suitable for smaller particles in suspension.
DLS measures particles in a liquid dispersion. A dry powder must therefore be dispersed in a suitable liquid before analysis. The choice of liquid and dispersion conditions is important because dissolution, agglomeration or poor dispersion can affect the measured particle size.
DLS measures particle size and particle size distribution in a liquid dispersion. Zeta potential analysis measures the electrical potential around dispersed particles and can provide information about dispersion stability. Zeta potential data can help assess whether nanoparticles are likely to remain dispersed or form agglomerates.
