![]() ![]() The results may be impacted by sedimentation though.įor the process of dynamic light scattering measurement particles are irradiated by a laser. The Stokes-Einstein equation relates the particle speed and the particle size to the hydrodynamic radius. ![]() Some of these necessary factors are the viscosity of the dispersion as well as its temperature. ![]() Subsequently, if you measure the speed of the particles by the dynamic light scattering method and also use further factors that influence the movement of the particles you can determine the hydrodynamic radius. For this you compare the intensity of the scattered light at two different moments on the same intensity track to receive the correlation function. The already discussed autocorrelation function serves as a mathematical description of the fluctuations of the scattered light and is used to determine the diffusion coefficient. As this transfer of energy is relatively constant, it has a bigger influence on smaller particles so they move much faster than bigger ones. Energy is passed on through these collisions of molecules, which causes particle movement. Thanks to this physical model from the 19th century we know that particles in a viscous medium randomly move in all directions and thereby collide with the particles of the solvent. The theoretical principle of dynamic light scattering is based on measuring Brownian motion. The curve decreases quickly for small particles and slowly for bigger particles. Hidden in this exponential decrease of the autocorrelation function is the information for particle size. This indicates the movement of a particle. For dynamic light scattering the autocorrelation function proceeds linearly at the beginning and then decreases exponentially. The measurement results are hidden in these fluctuations and interferences and can be converted into particle sizes and particle sizes distributions through autocorrelation. As the intensity of the scattered light varies, the fluctuation of smaller particles is faster, while bigger particles show higher amplitudes between the minimum and the maximum. For dynamic light scattering measurements this process is repeated multiple times over a period of time. Subsequently, a photo-electron multiplier (specific measurement diodes – mostly Avalanche photo-diodes for their light enhancing qualities) captures the interferences at a certain angle. The interaction between the particles and the laser beam forms scattered waves and when these waves overlap interferences occur, which can be directed through another polarizer (if one is present). As soon as the laser beam hits small particles inside the sample it is diffracted and scattered in all directions. Afterwards, the laser hits the sample that is located in a cuvette. If the phase position of the laser is precise enough, no polarizer is needed. In the DLS method a monochromatic laser beam is directed through a polarizer. ![]()
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