Dynamic Laser Light Scattering
Dynamic light scattering (also known as Photon Correlation Spectroscopy (PCS)) is the general designation for a method of determining the size of extremely small particles in the submicron range. These particles are found in Brownian motion in suspension or emulsion. The diffusion speeds for this are inversely proportional to the dimension dp (hydrodynamic diameter) of the particles.
(k = Boltzmann's contant)
Temperature T and viscosity η of the liquid are important parameters, which must be accurately known for the measuring of particle sizes.
Because of the Brownian motion of the particles, the back scattered light got a frequency shift (Doppler shift). The resulting intensity variation is recorded by a highly sensitive detector.
Because many conventional analyzers mathematically resolve the time dependency of the intensity variation by auto-correlation, the term photon correlation spectroscopy (PCS) has also become commonly used for this method. With these devices, the detection of the scattered light is made at a 90° angle to the incident laser light. However, the use of such analyzers is restricted to very dilute dispersions.
In contrast, the LB-550 works by utilizing the back scattering and employs modern evaluation algorithms based on Fast-Fourier transformation.