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a method of dynamic light scattering

Dynamic light scattering (DSR) - Dynamic light scattering (DLS), also known as photon correlation spectroscopy (photon correlation spectroscopy (PCS)) represents a method of measurement of particle sizes, is routine in a submicronic range.

Fig.

2.3. The evaluator «Zetasizer ZS» («Malvern Instruments Ltd.», the Great Britain) with He-Ne the laser (λ =633 nanometers) capacity 4 mvt

In the yielded work by means of method DSR on the device «Zetasizer ZS» firms «Malvern Instruments Ltd.» (Fig. 2.3) is measured particle size of filler in an aqueous slurry. Experiments by method DSR made in laboratory conditions at temperature 23°С with hallmarks of suspensions of powders of fillers described above in partition 2.1.1.

The size of submicronic particles is defined by method DSR by measurement of a diffusivity of disperse particles on the basis of the analysis of dynamic fluctuations of intensity of a diffused light. The disperse particles weighed in a liquid, participate in a thermal Brownian movement. Method DSR allows to measure a diffusivity of these particles and, hence, the size of disperse particles which is connected with a diffusivity.

On the basis of the measured speed of a Brownian movement the factor of forward diffusion D of particles directly pays off. This diffusivity is connected with hydrodynamic diameter of particles (Dh) the Stoke-ejnshtejna equation:

Where to - a Boltzmann's constant, T - absolute temperature, η - viscosity of solvent. The bottom dimensional limit of method DSR is defined by intensity of superfluous dispersion. Superfluous dispersion is a difference between dispersion from an investigated molecule or a particle and dispersanta in which it is. This difference in turn, depends on several factors, such as index of refractions of a particle and dispersanta, concentration of the sample, capacity and wave length of the used laser,

65 sensitivity of the detector and optical configuration of the evaluator. The size of a particle less, the it is less intensity of superfluous dispersion.

Depending on evaluator model «Zetasizer Nano ZS» there are distinctions in optical configuration (fig. 2.5). These distinctions are caused by angle of detecting of a diffused light: 173 ° - optical configuration () and 90 ° - optical configuration (). In the course of measurement of particle size the ray of light irradiated by the laser (1), passes through attenjuator (4) and gets to a dish with the sample (2). Dispersed by particles of the sample light is registered by the detector (3). Then the electric signal of the detector proportional to intensity of light, is processed by the correlator (5) on the mathematical algorithms which have been put in pawn in the software, and the calculated result in a kind of corresponding parametres of particle sizes is displayed on the screen of the computer (6). Attenjuator it is applied to easing of intensity of light incidenting on the sample of a beam as intensity of light dispersed by particles can appear out of detection limits of the detector because of excessive concentration of particles in the sample.

Fig. 2.4. The schema of measurement of particle sizes on evaluator "ZetasizerNano" [176]

Necessary level of easing of light attenjuatorom steals up automatically the evaluator software. Registration

Diffused light at angle 173 ° it is carried out in evaluator "ZetasizerNano" on the basis of the patented technology of detecting of back-scattering of light - NIBS (Non-InvasiveBack-Scatter), that allows to make measurements of particle sizes in a wide range of concentration.

2.2.3.

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A source: Sitnikova Vera Evgenievna. SPECTROSCOPIC STUDYING of STRUCTURE of POLYMERIC DISPERSE SYSTEMS. The dissertation on competition of a scientific degree of a Cand.Chem.Sci. Tver - 2015. 2015

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