![]() Therefore, the diffusion coefficient and either particle size or viscosity can be found by fitting the measured correlation function to a single exponential function.Ī characteristic autocorrelation function of the scattered light is shown below where the baseline b is proportional to the total intensity I, and it can be determined experimentally. For the simplest case of spherical monodisperse non-interacting particles in a dust-free fluid, the characteristic decay time of the correlation function is inversely proportional to the linewidth of the spectrum. Information about the light-scattering spectrum can be obtained from the autocorrelation function G(τ) of the light-scattering intensity. Where k B is the Boltzmann constant, T the temperature, and η the shear viscosity of the solvent. With the assumption that the particles are spherical and non-interacting, the mean radius is obtained from the Stokes-Einstein equation N is the refractive index of the medium, λ the laser wavelength, and θ the scattering angle. The linewidth of the light scattered spectrum Γ (defined as the half-width at half-maximum) is proportional to the diffusion coefficient of the particles D (Eq.1): ![]() This in turn results in fluctuations of intensity of the scattered light. The disperse particles or macromolecules suspended in a liquid medium undergo Brownian motion which causes the fluctuations of the local concentration of the particles, resulting in local inhomogeneities of the refractive index. The PCS method consists in determining the velocity distribution of particles movement by measuring dynamic fluctuations of intensity of scattered light. The diffusion coefficient can be translated into a hydrodynamically effective radius via the Stokes-Einstein relation.Photocor particle size analyzers is based on the Dynamic light scattering (DLS) technique and designed for measurements of sub-micron particle sizes, diffusion coefficients, viscosities, molecular weights of polymers in basic and applied studies. Squared radius of gyration, form factor and diffusion coefficient are z-averaged values. The molar mass is a weight averaged molecular weight. This enables to follow growth processes with a time resolution of 10 s.Īccessible Quantities: molar mass, squared radius of gyration, form factor, diffusion coefficient and its distribution. The Instrument makes available for the first time a simultaneous recording of the time resolved evolution of the particle mass, the geometric size and the diffusion coefficient (together with the corresponding hydrodynamically effective radius) and its distribution. The particles usually are smaller than a micrometer.Įvaluation of dynamic light scattering reveals a diffusion coefficient (and its distribution in case of polydisperse samples) of scattering polymers and colloids. ![]() Regime of momentum transfer: 0.0050 nm -1 < q < 0.027 nm -1 (depends on solvent)Įvaluation of static light scattering reveals a weight averaged molar mass, a mean squared radius of gyration and a form factor of scattering polymers and colloids. Regime of observation angles: 20° < Θ < 136° A laser at a wavelength of 632.8 nm and a power of 35 mW (Soliton HeNe) is used as a light source. The ALV/CGS-3/MD-8 Multidetection Laser Light Scattering Goniometer System simultaneously analyzes static and dynamic light scattering at 8 different observation angles. ![]()
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