static light scattering vs dynamic light scattering

To still evaluate the weak signals from very small particles, scattered light measurement is performed with shorter wavelengths, which generally provides stronger signals. With decreasing particle size, the overall intensity of the scattered light decreases, and less light is scattered in forward direction, and more is scattered to the side. The light scattering pattern is rather diffuse, but more light is scattered in forward direction than to the side or back. Furthermore, the intensity of the diffraction maxima would increase.įor the 1 µm particles these diffraction rings are no longer observed. For larger particles, the diffraction angles would be smaller, and the rings would be closer to the center. The figure shows the scattered light patterns of suspensions with 1 µm and 10 µm particle size, respectively.įor the 10 µm particles, the scattered light pattern shows a characteristic ring structure, which can be explained mainly by diffraction. Static light scattering is often referred to as laser diffraction or laser diffractometry, even independent of the size of the particles considered and the phenomena that occur. Literature values are available for the refractive indices of almost all solids, so Mie theory can be applied very reliably for static light scattering. This is described by the Mie theory, which, however, also includes diffraction and therefore allows a comprehensive evaluation of light scattering phenomena. 'Large particles' in this context means 'significantly larger than the wavelength of light'.įor the description and evaluation of scattered light patterns of smaller particles, the optical properties, essentially the refractive index, must be considered. This is sufficiently described by the so-called Fraunhofer theory. The characteristic light scattering patterns which are formed when a laser interacts with particles are caused by diffraction, refraction, reflection, and absorption (as shown on the figure).įor large particles, diffraction, which occurs at the contour of particles, is the dominant mechanism.

Static light scattering vs dynamic light scattering