The ACF can be evaluated by the CONTIN algorithm according to Provencher ( 1982), which allows to fit even a complex decay of correlation in polydisperse solutions to calculate the respective diffusion constants (D) and process the data.
Decay time constants of small particles are shorter in agreement with the dependency of diffusion speed on particle mass (Fig. Depending on how fast particles are diffusing, the correlation decay time constants, which are derived from the exponential auto-correlation function (ACF) are individually different. Scattering intensity pattern are correlated with themselves (auto- correlation) after short delay intervals of time (τ) to monitor the continuous decay of correlation. 6.2), which results in characteristic size- dependent fluctuation intervals of the electric field component of the scattered light. This is explained by Brownian motion of particles in and around the sample volume that is in focus of the laser (Fig. The number of photons hitting the detector, which can be a photo-multiplier tube, is fluctuating over time.
The laser light that is scattered by the particles inside a small focal volume of a DLS sample is continuously recorded and quantified by a photon-counting detector positioned at a specific angle if not hindered by other geometrical restraints, an angle of 90° might be suitable for the experimental setup.
In this paper, the theory of dynamic light scattering technique and the mathematical principles of measurement are briefly presented.In general, all kinds of particles scatter electromagnetic waves in all directions, depending on their size isotropically or anisotropically. The application of this technique is expanding in the fields of nanomaterials, physics, chemistry, biology, medicine and fluid mechanics rapidly. Due to the reliable results providing by the technique, it is very popular in universities laboratories and industrial institutes. It is also a non-invasive, fast, easy, accurate, reliable and relatively inexpensive technology which requires very low amount of sample and low maintenance cost.Īlthough, this technique has got limitations such as: results fluctuations due to changes in temperature and viscosity sample preparation refractive index and a must for dispersed particles in Solution regarding to the physical and chemical interaction of the particles with the liquid, finding a right solution is a matter of difficulty. This spectroscopy method performs measurements at the nano scale and micro scale indirectly. When monochromatic light beam incidents to moving particles the intensity of the incoming light changes randomly, depending on the size of the particles. Brownian motion phenomena of the particles in solutions is used to determine the particle size distribution. This approach is one of the most general methods used to determine the particle size distribution. Dynamic light scattering is an optical measurement technique for describing nanoparticle systems. Particle size characterization affects many material properties and is a valuable factor of quality and performance.
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