There are many methods in finding polydispersity, one method could be light scattering. In this method, the scattering of light and other electromagnetic radiation will be used. That the deflection of rays in random directions using irregularities in propagation medium. To a surface between two media. It is also called diffuse reflection. Using the interaction of light with matter can shed light on important information about the structure and dynamics of the material being examined.
If the scattering centers are in motion, then the scattered radiation is doppler shifted. An analysis of the spectrum of scattered light can thus yield information regarding the motion of the scattering center. Periodicity or structural repetition in the scattering medium will cause interference in the spectrum of scattered light. Thus, a study of the scattered light intensity as a function of scattering angle gives information about the structure, spatial configuration, or morphology of the scattering medium.
In regards to light scattering in liquids and solids, primary material considerations include Crystalline structure is How close-packed its atoms or molecules are, and whether or not the atoms or molecules exhibit the long-range order evidenced in crystalline solids. Glassy structure is scattering centers include fluctuations in density and/or composition. Microstructure Scattering centers include internal surfaces in liquids due largely to density fluctuations, and microstructural defects in solids such as grains, grain boundaries, and microscopic pores.
In the process of light scattering, the most critical factor is the length scale of any or all of these structural features relative to the wavelength of the light being scattered. An extensive review of light scattering in fluids has covered most of the mechanisms which contribute to the spectrum of scattered light in liquids, including density, anisotropy, and concentration fluctuations. Thus, the study of light scattering by thermally driven density fluctuations (or Brillouin scattering) has been utilized successfully for the measurement of structural relaxation and viscoelasticity in liquids, as well as phase separation, vitrification and compressibility in glasses.
In addition, the introduction of dynamic light scattering and photon correlation spectroscopy has made possible the measurement of the time dependence of spatial correlations in liquids and glasses in the relaxation time gap between 10? and 10? 2 s in addition to even shorter time scales – or faster relaxation events. It has therefore become quite clear that light scattering is an extremely useful tool for monitoring the dynamics of structural relaxation in glasses on various temporal and spatial scales and therefore provides an ideal tool for quantifying the capacity of various glass compositions for guided light wave transmission well into the far infrared portions of the electromagnetic spectrum.
So, in application we could use Brillouin scattering that could result from the interaction of light photons with acoustic or vibrational quanta (phonons). The scattering is caused by the diffraction of incident planar monochromatic light waves by spontaneous, sinusoidal density fluctuations (i. e. standing thermal sound waves, or acoustic phonons). The light wave is considered to be scattered by the density maximum or amplitude of the acoustic phonon, in the same manner that X-rays are scattered by the crystal planes in a solid.
The role of the crystal planes in this process is analogous to the planes of the sound waves or density fluctuations. The interaction consists of an inelastic scattering process in which a phonon is either created or annihilated. The energy (and thus the frequency) of the scattered light is slightly increased or decreased. In this way we could put a chamer in the factory with the means of scattering light. It is good in temperature cause it does not emit much. Due to it uses a very small wavelength. By scattreing light we could easily determine the polydispersity of the material.