| Recently, studying the properties of nano-particles in colloidal suspension is an important research field with great promise. The ion concentration, valence, temperature and so on of the electrolyte can change the hydrokinetics radius of the nano-particles in colloidal suspension by varying the double electrode layer thickness. Dynamic light scattering method can measure translational scattering coefficient of the colloidal suspension with the slight frequency shift quantity of the scattered light caused by the Brownian movement. With that, we can obtain the properties of particles. The dynamic scattering light technology has been widely used at the measurement of particle radius,as a non-contact\non-destruction method in optical detection.In this paper, We introduced the fundamental theories of low-coherence dynamic scattering light and set up our experiment system, also studying the diffusion properties of nano-particles in the colloidal suspension. We made an introduction of double electrode layer theory and its model. According to the single scattering theory and considering the effective diffusion coefficient, we discussed the influence of electrolyte on the particle radius in the colloidal suspension on the basis of the double electrode layer theory. We respectively measured the influence of electrolytic ion concentration and valence on hydrodynamic radius of particles in the polystylene suspension, with radii of 400nm and 550nm, respectively. The volume fraction of both suspensions were 10%. The experiment results implied that:in the electrolytes, added with different ion concentrations of Nacl and CaCl2, the vary of double electrode layer declined as the increase of ion concentrations, as a result, the hydrodynamic radius of particles declined too. In the electrolytes, added with the same ion concentration of NaCl and CaCl2, the vary of double electrode layer caused by the CaCl2 was small, and the hydrodynamic radius of particles become small as well. |
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