Particle-size determination by low-angle light scattering: effect of refractive index

Area of Science:

• Physics
• Optical Sciences
• Materials Science

Background:

• Accurate particle size determination is crucial in various scientific fields.
• Mie theory provides an exact solution for light scattering by homogeneous spheres.
• The Sloan method utilizes the angular position of a scattering intensity maximum to estimate particle radius.

Purpose of the Study:

• To validate the accuracy of the Sloan method for particle radius determination.
• To investigate the influence of sphere size and refractive index on scattering intensity maxima.
• To assess the applicability of the Sloan method across a range of particle sizes and optical properties.

Main Methods:

• Exact Mie theory calculations were performed for light scattering intensity.
• Simulations covered sphere radii from 0.1 to 100 micrometers at a wavelength of 5461 Å.
• Calculations included transparent (m' = 0) and absorbing spheres with varying real (m) and imaginary (m') refractive indices.

Main Results:

• The location of the first maximum in I(theta)θ² was analyzed.
• The Sloan method's assumption of refractive index independence was confirmed for radii > 10 micrometers.
• For particles smaller than 10 micrometers, the refractive index significantly affected the maximum's angular position.

Conclusions:

• The Sloan method is a reliable technique for particle radius determination for spheres above 10 micrometers.
• The refractive index must be considered when applying the Sloan method to smaller particles.
• These findings refine the understanding of light scattering applications in particle sizing.