![]() The instrumental implementation of static light scattering in a measuring device is shown in the Figure. This must be taken into account accordingly when evaluating and calculating the particle size distribution. Real samples usually contain many different particle sizes, all of which contribute to the total scattered light. The figure also shows light scattering patterns from a mixture of 1 µm and 10 µm particles, with the scattering patterns of the two sizes overlapping. 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. ![]() Irregularly-shaped particles induce broad size distributions because both width and length are considered as individual particles.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. Therefore, particle shape can not be identified. Laser diffraction assumes that all signals originate from particles that are ideally spherical. ![]() The recirculation system of the equipment ensures the total homogenization of the sample. Wet samples like emulsions are suspended in a liquid, and powders are analyzed in an air stream. Laser diffraction is suitable for wet and dry samples. It is a valuable analysis parameter for research and product development purposes in multiple industries. Particle size is an important characteristic of powders and particulate materials. Large particles scatter light at a high intensity, while small particles do so at a low intensity. Particle size also affects scattering intensity. Large particles scatter light at small angles, and a decrease in particle size increases the scattering angle logarithmically. Laser diffraction equipment detects the intensity distributions of laser light scatters from multiple particles simultaneously.įraunhofer diffraction theory states that the intensity of light scattering is directly proportional to particle size. Light propagates from the edges of particles as spherical wavefronts, and interactions between the light and the particles lead to the diffraction phenomenon. The diffraction phenomenon occurs when monochromatic, coherent, and polarized light hits an object. A mathematical model based on the Fraunhofer and Mie theories is applied to determine the particle size distribution. Laser diffraction measures the scattering intensity of light from particles in a suspension as a function of scattering angle, light wavelength, and light polarization. Laser diffraction is based on the indirect calculation of particle sizes from the diffraction patterns of particles. Laser diffraction has a wide dynamic range, as it can detect particles from 0.02 µm to 2 mm. During the analysis, a laser beam is passed through a sample in liquid suspension or dry powder dispersion form. Laser diffraction (LD), also known as static laser light scattering (SLS) is one of the most popular ways to analyze particle size distribution. Particle size distribution analysis with laser diffraction
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |