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Introduction to Laser Diffraction

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Ian Treviranus, Product Line Manager for HORIBA Particle, discusses fundamental principles and practical considerations of laser diffraction for particle size analysis. …

Ian Treviranus, Product Line Manager for HORIBA Particle, discusses fundamental principles and practical considerations of laser diffraction for particle size analysis.

This presentation is archived with the original webinar video in the Download Center at www.horiba.com/us/particle.

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  • 1. Introduction to Laser Diffraction Fundamental Principles and Everyday Uses Ian Treviranus ian.treviranus@horiba.com www.horiba.com/us/particle© 2011 HORIBA, Ltd. All rights reserved.
  • 2. Plan of Attack How does it work? What can diffraction do? How does it help you? Strong points, weak spots Q&A© 2011 HORIBA, Ltd. All rights reserved.
  • 3. Core Principle Can investigate a particle with light and derive its size© 2011 HORIBA, Ltd. All rights reserved.
  • 4. Core Principle Why? Because the angle and intensity of the scattered light depends on its size Larger Particle Smaller Particle© 2011 HORIBA, Ltd. All rights reserved.
  • 5. Core Principle So all we need is a light source, a particle, light detectors, and a German mathematician Joseph von Fraunhofer Gustav Mie or …but this guy has a better solution© 2011 HORIBA, Ltd. All rights reserved.
  • 6. Four Types of Interaction Diffraction Reflected Refracted Refraction Absorbed and Reradiated Reflection Diffracted Absorption© 2011 HORIBA, Ltd. All rights reserved.
  • 7. Edge Diffraction© 2011 HORIBA, Ltd. All rights reserved.
  • 8. Diffraction Patterns© 2011 HORIBA, Ltd. All rights reserved.
  • 9. Why a “pattern”?© 2011 HORIBA, Ltd. All rights reserved.
  • 10. Double Slit = Single SlitSingle slit diffraction pattern Double slit diffraction pattern© 2011 HORIBA, Ltd. All rights reserved.
  • 11. A “particle” in disguise Light Scatter occurs whether from a slit, a pinhole or a particle. It occurs at the edge of an object. A SLIT and θ PARTICLE of the same size produce the same diffraction pattern θ θ© 2011 HORIBA, Ltd. All rights reserved.
  • 12. Size affects angle Large particles scatter light through SMALLER angles θ Small particles scatter light through LARGER anglesLarge Particle θ Small Particle © 2011 HORIBA, Ltd. All rights reserved.
  • 13. Size affects intensity LARGE PARTICLE: Low angle scatter Large signal Wide Pattern - Low intensity SMALL PARTICLE: Narrow Pattern - High intensity High Angle Scatter Small Signal© 2011 HORIBA, Ltd. All rights reserved.
  • 14. Other factors Size, Shape, and Optical Properties also affect the angle and intensity of scattered light Extremely difficult to extract shape information without a priori knowledge Assume hard sphere model Optical properties (refractive index) explain refraction Key difference between Fraunhofer and Mie© 2011 HORIBA, Ltd. All rights reserved.
  • 15. Plan of Attack How does it work? What can diffraction do? How does it help you? Strong points, weak spots Q&A© 2011 HORIBA, Ltd. All rights reserved.
  • 16. Most flexible size analysis The core relationship between size and scattered light works for: Nanoparticles Small micronized particles Large micronized particles Wide dynamic size range© 2011 HORIBA, Ltd. All rights reserved.
  • 17. Most flexible size analysis The core relationship between size and scattered light works for: Suspensions – solid-liquid Powders – solid-gas Emulsions – liquid-liquid Flexible sample types© 2011 HORIBA, Ltd. All rights reserved.
  • 18. Most flexible sizing Wide dynamic size range Multiple sample types No a priori information needed to monitor size change Accuracy is improved with refractive index (when smaller than approx. 30 microns) Very fast measurement think seconds, not minutes Easy to use, easy to interpret First principal measurement no calibration© 2011 HORIBA, Ltd. All rights reserved.
  • 19. Nanoparticle Sensitivity Laser diffraction can measure 30 nm! Typical setup is 2 light sources: red & blue 30, 40, 50, 70 nm latex standards 30 nm colloidal silica© 2011 HORIBA, Ltd. All rights reserved.
  • 20. Nanoparticle Sensitivity Some (unfounded?) concerns with particles < 100 nm Diffraction good at determining sub-100 nm particles in presence of larger particles Software set to display % under any given size Data shown left is for skin cream and TiO2 suspension© 2011 HORIBA, Ltd. All rights reserved.
  • 21. Large Particle Sensitivity 14 100 90 12 80 10 70 60 8 Coffee Results q(%) 50 6 40 4 30 20 2 10 0 0 10.00 100.0 1000 3000 Diameter(µm)© 2011 HORIBA, Ltd. All rights reserved.
  • 22. Flexible Sample Handlers 10 ml 35 ml 200 ml powders •Wide range of sample cells depending on application •High sensitivity keeps sample requirements at minimum •Technology has advanced to remove trade-offs© 2011 HORIBA, Ltd. All rights reserved.
  • 23. Plan of Attack How does it work? What can diffraction do? How does it help you? Strong points, weak spots Q&A© 2011 HORIBA, Ltd. All rights reserved.
  • 24. Monitor Process Quality •Black size distribution is internal standard •Red result is considered a passing batch •Blue result is a bad batch •Highlights problem in production •All accomplished with complex product formulation© 2011 HORIBA, Ltd. All rights reserved.
  • 25. Monitor Product Quality Median (Peak 1) : 0.031 μm Median (Peak 2) : 1.75 μm 0.05wt% •Product quality and performance can be located at tails •Diffraction is “resolution limited” technique, but can still have success finding outlier populations© 2011 HORIBA, Ltd. All rights reserved.
  • 26. Minimize Sample (MiniFlow) Colloidal Silica (weak scatterer) Magnesium Stearate Median (D50): 35 nm Median (D50): 9.33 μm Sample Amount: 132 mg Sample Amount: 0.165 mg Bio-degradable Polymer Median (D50): 114 μm Sample Amount: 1.29 mg© 2011 HORIBA, Ltd. All rights reserved.
  • 27. Measurement Workflow Prepare the sample Good sampling and dispersion a must! May need to use surfactant or admixture© 2011 HORIBA, Ltd. All rights reserved.
  • 28. Measurement Workflow Prepare the system Align laser to maximize signal-to-noise Acquire blank/background to reduce noise© 2011 HORIBA, Ltd. All rights reserved.
  • 29. Measurement Workflow Introduce sample Add sample to specific concentration range Pump sample through measurement zone Final dispersion (ultrasonic)© 2011 HORIBA, Ltd. All rights reserved.
  • 30. Measurement Workflow© 2011 HORIBA, Ltd. All rights reserved.
  • 31. Measurement Workflow Measurement Click “Measure” button – Hardware measures scattered light distribution – Software then calculates size distribution© 2011 HORIBA, Ltd. All rights reserved.
  • 32. Iterative Calculation© 2011 HORIBA, Ltd. All rights reserved.
  • 33. LA-950 Method Expert There are four important tests… Circulation Concentration Dispersion Duration© 2011 HORIBA, Ltd. All rights reserved.
  • 34. LA-950 Method Expert There are two important tests… Real RI Imaginary RI© 2011 HORIBA, Ltd. All rights reserved.
  • 35. LA-950 Method Expert Why is the test important? What does the test do? How will the results be displayed? What is the best value? User selects up to 5 values for testing© 2011 HORIBA, Ltd. All rights reserved.
  • 36. LA-950 Method Expert Method Expert guides user to prepare the LA-950 for each test Results displayed in multiple formats: PSD, D50, R-parameter© 2011 HORIBA, Ltd. All rights reserved.
  • 37. LA-950 Method Expert© 2011 HORIBA, Ltd. All rights reserved.
  • 38. LA-950 Method Expert© 2011 HORIBA, Ltd. All rights reserved.
  • 39. Plan of Attack How does it work? What can diffraction do? How does it help you? Strong points, weak spots Q&A© 2011 HORIBA, Ltd. All rights reserved.
  • 40. Diffraction Drawbacks Assumes hard spherical model Most materials are aspherical Error is introduced Data cannot be directly compared to other techniques measuring different property© 2011 HORIBA, Ltd. All rights reserved.
  • 41. Diffraction Drawbacks “Optical” concentration range Dilution can cause stability issues Especially difficult for creams and pastes© 2011 HORIBA, Ltd. All rights reserved.
  • 42. Diffraction Drawbacks Volume basis by default Although excellent for mass balancing, cannot calculate number basis without significant error Number Volume Area© 2011 HORIBA, Ltd. All rights reserved.
  • 43. The Benefits Wide size range Most advanced analyzer measures from 30 nano to 3 milli Flexible sample handlers Powders, suspensions, emulsions, pastes, creams Very fast Allows for high throughput, 100’s of samples/day Easy to use Many instruments are highly automated with self-guided software Good design = Excellent precision Reduces unnecessary investigation/downtime First principle measurement No calibration necessary Massive global establishment© 2011 HORIBA, Ltd. All rights reserved.
  • 44. Plan of Attack How does it work? What can diffraction do? How does it help you? Strong points, weak spots Q&A© 2011 HORIBA, Ltd. All rights reserved.
  • 45. For More Information ISO 13320:2009 – the go-to guidance resource Particle Size Measurements; Fundamentals, Practice, Quality by Henk Merkus Visit www.horiba.com/us/particle Previously recorded webinars: -- Laser Diffraction Performance -- LA-950 Method Expert Software -- Understanding and Interpreting Your PSA Results -- Setting Attainable Size Specifications -- “Boot Camp” Laser Diffraction 6-part Training Course Many application and technical notes Ask a question at labinfo@horiba.com Keep reading the monthly HORIBA Particle e-mail newsletter! Visit the Download Center to find the video and slides from this webinar.© 2011 HORIBA, Ltd. All rights reserved.

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