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 is not necessary - easily verified using standard reference materials.
- Well established technique - covered by ISO13320 (2020).
For these reasons, laser diffraction is becoming the standard particle sizing technique across many industry sectors, being faster, simpler and having better resolution than more traditional sizing techniques such as sieve analysis.
Principles of laser diffraction
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. 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.
Applications of laser diffraction technology
Laser diffraction technology finds extensive applications across a wide range of industries due to its versatility, accuracy, and efficiency in particle size analysis.
Here are some key areas where laser diffraction, including products like the Mastersizer, Spraytec, and Insitec, play a crucial role.
Pharmaceutical Industry
In the pharmaceutical industry, laser diffraction analyzers such as the Mastersizer are used for the characterization of drug particles, excipients, and formulations.
They enable precise control over particle size distribution, ensuring uniformity and stability of pharmaceutical products.
Additionally, instruments like the Spraytec are utilized for the analysis of spray particle size in inhalation drug delivery systems, optimizing aerosol performance and drug delivery efficiency.
Chemical Industry
Laser diffraction technology is utilized for the analysis of various particulate materials including polymers, pigments, and catalysts.
Instruments like the Mastersizer provide valuable insights into particle size distribution and surface area, facilitating quality control and process optimization.
Moreover, the Insitec range of analyzers offers real-time particle size monitoring in chemical manufacturing processes, ensuring product consistency and minimizing waste.
Food and Beverage Industry
In the food and beverage industry, laser diffraction analyzers play a crucial role in the analysis of ingredients, additives, and powders.
The Mastersizer series is used for assessing particle size distribution in food ingredients such as flour, sugar, and spices, ensuring the desired texture of food products.
Similarly, the Spraytec analyzer is employed for characterizing the particle size distribution of emulsions and suspensions, optimizing product stability and shelf life.
Environmental Monitoring
Instruments like the Mastersizer and Insitec, are employed in environmental monitoring applications for the analysis of particulate pollutants, aerosols, and sediments.
These analyzers provide valuable data for assessing air and water quality, studying particle dynamics, and understanding the impact of pollutants on ecosystems.
Real-time monitoring capabilities of instruments such as the Insitec range enable timely intervention and management of environmental contaminants.
Research and Development
Across various research fields, laser diffraction analyzers such as the Mastersizer, Spraytec, and Insitec serve as valuable tools for studying particle size distribution, morphology, and aggregation behavior.
They facilitate fundamental research in areas such as materials science, nanotechnology, and colloidal chemistry, driving innovation and discovery.
The flexibility and accuracy of these instruments enable researchers to explore new applications and push the boundaries of scientific knowledge.
Process Control and Optimization
In manufacturing and industrial processes, laser diffraction technology is employed for real-time monitoring and control of particle size parameters. Instruments like the Insitec range provide continuous particle size analysis, enabling operators to optimize process efficiency, ensure product quality, and minimize waste and production costs. The Mastersizer and Spraytec analyzers offer robust solutions for offline particle size measurement, supporting process optimization across various industries.
By offering rapid and reliable particle size analysis, laser diffraction technology - including products like the Mastersizer, Spraytec, and Insitec - continues to revolutionize diverse industries, enabling advancements in product development, quality assurance, and scientific research.
