Also known as Low Angle Light Scattering (LALS), Fraunhofer diffraction, or Mie Scattering.

Fraunhofer diffraction is the simplest method of determining particle size from light scattering measurements. It applies to particles larger than approximately one micron.

For particles larger than the wavelength of light, the light scatters from the edge of the particle at an angle which is dependent on the size of the particle. Larger particles scatter light at relatively smaller angles than light scattered from smaller particles. From observing the intensity of light scattered at different angles, we can determine the relative amounts of different size particles.

As the particles get close to or smaller than the wavelength of light, more of the light intensity is scattered to higher angles and back-scattered. The Mie Scattering Theory accounts for this different behavior and requires that we input information about the optical properties of the particles, such as refractive index. In order to make particle size measurements, the light intensity pattern must be measured over the full angular range. The Mie Theory applies to all sizes. When the particle size is larger that the wavelength of the incident light, the Mie equation reduces to the Fraunhofer equation. This allows one algorithm to cover the entire size range.

HORIBA incorporates the full Mie Scattering Theory over the entire size range of interest. An array of detectors. including high-angle and back-scatter detectors, and multiple light sources of different wavelengths are employed to provide an instrument that allows measurement of the full size range in one analysis. There is no need to combine results from two optical systems or analysis techniques, along with the problems that entails.

HORIBA offers a range of static light scattering particle size analyzers with different size ranges and with a range of capabilities.

• Partica LA-950 0.01-3000µm
• LA-930 0.02-2000µm
• LA-300 0.1-600µm

Other HORIBA particle size analyzers

Also known as Photon Correlation Spectroscopy (PCS).

Dynamic light scattering (DLS) (also known as photon correlation spectroscopy or quasi-elastic light scattering) is an analytical technique used to determine the size distribution of small particles in suspension or polymers in solution. Particles in this size range experience Brownian motion as the result of the interaction with the molecules of the suspending fluid, with larger particles moving more quickly and smaller particles moving more slowly. The velocity of the moving particles can be used to determine the translational diffusion coefficient through the use of an auto-correaltor and correlation function. The Stokes Einstein equation, below, is then used to calculate particle radius (or diameter).

The size value reported is the hydrodynamic diameter - the diameter of a sphere that diffuses at the rate detected by the instrument. This diameter includes both the core particle plus any surface structure such as bonded polymer. The hydrodynamic diameter is also affected by the presence of the attached electric double layer so surface chemistry such as ionic strength of the suspending medium can also influence the reported results.

The SZ-100 can perform particle size measurements at both 90° and backscatter (173°) in order to accommodate the widest possible range of samples. Certain samples may scatter light more efficiently at 90° while high concentration samples may be better analyzed near the cell wall at 173° in order to minimize multiple scattering effects. Automatic attenuators optimize the amount of scattered light reaching the detectors, facilitating the analysis from small, low concentration samples to highly concentrated suspension.

The same instrument can also be used to measure other particle properties including molecular weight (MW), second virial coefficient (A2), and zeta potential. MW and A2 data is generated from a Debye plot using static slight scattering measurements at several sample concentrations. Zeta potential is determined using a range of cells that apply an electric field to the sample and measuring the frequency shift from the motion of the particles due to the applied field.

HORIBA offers the SZ-100 nanoPartica Dynamic Light Scattering Particle Size Analyzer, covering a range of 03nm to µm.

Learn more about the SZ-100

Learn more about other HORIBA particle size analyzers

Digital image processing captures images of the particles of interest with a CCD camera. Image analysis software interprets these images to provide particle size information, as well as particle shape parameters. The CCD camera is similar to those found in digital cameras.

Developed by Retsch Technology and distributed by HORIBA Instruments, the Camsizer utilizes two Full Frame cameras with matched scales of reproduction to capture images of particles in the measurement zone. This patented technique allows a full frame measurement for the larger particles and the zoom camera to provide high resolution images of the smaller particles.

The Camsizer's software package provides powerful data analysis and reporting capabilities, allowing the user to select from a wide range of particle size or shape parameters. The technique also allows for a very wide size range, 30 microns to 30 millimeters, although particles up to 90mm can be measured.

Camsizer

Other HORIBA particle size analyzers