Laser diffraction (LD) is used for particle size distribution analysis, it detects particle sizes from 0.02 µm to 2 mm. LD is used to analyse liquid and dry powder samples. Particle size is one of the most important analysis parameters of powders and particulate materials. LD is a nondestructive method.
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Laser diffraction (LD), also known as static laser light scattering (SLS) is one of the most popular ways to analyse the particle size distribution. Laser beam is passed through a sample that is in liquid suspension or in dry powder dispersion. LD has a wide dynamic range, it can detect particles from 0.02 µm to 2 mm.
Particle size is an important characteristic of powders and particulate materials. It is a valuable analysis parameter for research and product development applications.
In LD particle sizes are measured indirectly from diffraction patterns. LD measures scattering intensity from particles in suspension as a function of scattering angle, light wavelength and light polarization. A mathematical model based on the Fraunhofer theory and the Mie theory is applied to determine the particle size distribution.
Diffraction phenomenon occurs when monochromatic, coherent and polarized light hits an object. Light propagates from the edges of particle as spherical wave fronts, interactions between light and particle lead to the diffraction phenomenon.
LD detects intensity distributions of laser light scatters from multiple particles simultaneously. Fraunhofer diffraction theory states that the intensity of light scatter is directly proportional to the particle size. Large particles scatter light to small angles, decrease in particle size increases logarithmically the scattering angle. Also, particle size affects scattering intensity. Large particles scatter light at high intensity and small particles scatter intensity is low.
LD is used for wet and dry samples. Wet samples like emulsions are suspended to liquid. Recirculation system sample ensures the total homogenization of the sample. Powders are analysed in an air stream.
LD assumes that all signals originate from particles that are ideal sphericals. Therefore particle shape can not be identified. Irregular shaped particles induce broad size distributions because both width and length are considered as individual particles.
Suitable sample matrices
- Coating materials
Ideal uses of laser diffraction
- Laser Diffraction is used to analyse particle size distributions in liquid suspension or in powder dispersion.
- Particle size distribution analysis is used in food development because particle size has a significant influence on food flavor.
- Dry powders like pigments are analysed with a laser diffractometer because particle size affects the colouring power of a pigment.
Frequently asked questions
Laser diffraction is used for analysing particle size distribution in liquids and dry powders.
LD is used in soil studies, to analyse grain size distributions in soil, and, and sediment samples.
Laser diffraction assumes that all particles are ideal sphericals, therefore particles with irregular shape induce broad size distributions.
Laser Diffraction does not provide information about particle shape.
Laser diffraction samples can be liquids and dry powders.
In some cases samples are suspended into liquid, this is done for example to emulsions.
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