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Laser diffraction is a widely used particle sizing technique for materials ranging from hundreds of nanometers up to several millimeters in size. The main reasons for its success are:

  • Wide dynamic range - from submicron to the millimeter size range.
  • Rapid measurements - results generated in less than a minute.
  • Repeatability - large numbers of particles are sampled in each measurement.
  • Instant feedback - monitor and control the particle dispersion process.
  • High sample throughput - hundreds of measurements per day.
  • Calibration not necessary - easily verified using standard reference materials.
  • Well established technique - covered by ISO13320 (2009).

Principles

Laser diffraction measures particle size distributions by measuring the angular variation in intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles relative to the laser beam and small particles scatter light at large angles, as illustrated below. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory of light scattering. The particle size is reported as a volume equivalent sphere diameter.

Optical properties

Laser diffraction uses Mie theory of light scattering to calculate the particle size distribution, assuming a volume equivalent sphere model.

Mie theory requires knowledge of the optical properties (refractive index and imaginary component) of both the sample being measured, along with the refractive index of the dispersant. Usually the optical properties of the dispersant are relatively easy to find from published data, and many modern instruments will have in-built databases that include common dispersants. For samples where the optical properties are not known, the user can either measure them or estimate them using an iterative approach based upon the goodness of fit between the modeled data and the actual data collected for the sample.

A simplified approach is to use the Fraunhofer approximation, which does not require knowledge of the optical properties of the sample. This can provide accurate results for large particles. However it should be used with caution whenever working with samples which might have particles below 50µm or where the particles are relatively transparent.

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Particle Sizing Masterclass 3: method development Webinar - Live (English)

In this third webinar in the particle sizing masterclass we will look at method development and we will concentrate on the techniques of laser diffraction and automated image analysis. The most important thing in method development is always to make ...

Date:
April 28 2015
Language:
English

Keywords: English Particle size Laser diffraction Webinar - Live Eastern Time 

Masterclass 2: Desarrollo de métodos de dispersión líquida utilizando la técnica de difracción láser Webinar - Recorded (Spanish)

Este webinario cubrirá el desarrollo de métodos para muestras dispersas en líquidos. Se hará un análisis de los factores que afectan la medición, como el muestreo y la dispersión, y la importancia relativa de estos factores en diferentes rangos de ta...

Product:
Mastersizer 3000
Date recorded:
March 25 2015
Language:
Spanish

Keywords: Mastersizer 3000 Particle shape Particle size Laser diffraction Webinar - Recorded Mexico Time Spanish 

What are the benefits of owning a Malvern particle size analyzer? Whitepaper (English)

Why can you trust Malvern when purchasing a particle size analyzer? These results of a recent customer survey highlight the reasons why Malvern's customers chose the Mastersizer and Spraytec laser diffraction systems to meet their particle size measu...


Keywords: English Whitepaper Mastersizer range Spraytec Particle size Laser diffraction 

Particle Size Masterclass 2: which technique is best for me? Webinar - Recorded (English)

In the second webinar in the particle size masterclass series, we follow on from why you need to measure particle size, covered in the first masterclass, by looking at how to measure particle size. We started with considerations for choosing a partic...

Date recorded:
March 19 2015
Language:
English

Keywords: English Particle size Dynamic Light Scattering Image analysis Laser diffraction Webinar - Recorded Eastern Time Nanoparticle Tracking Analysis 

Suspension Stability: Why particle size, zeta potential and rheology are important Poster (English)

Why particle size, zeta potential and rheology are important. This poster discusses the importance of particle size, zeta potential and rheology for dispersion stability and how they can be manipulated to enhance stability


Keywords: Suspensions, slurries and pastes English Poster Particle size Rheology and viscosity Zeta potential Electrophoretic Light Scattering Laser diffraction Rheometry - rotational 
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