Translated Abstract
As a fundamental thermophysical property of liquids, viscosity is essential in the fields of energy, chemical and biological medicine. Dynamic light scattering method (DLS) is a novel, fast and non-contact detection technology and it requires less samples and time compared with other viscosity measurement methods. However, due to the immature application of DLS method in the measurement of liquid viscosity, there are some fundamental issues which need to be improved. In the present work, focusing on the problems of DLS principle, the main work in this thesis are listed as follows:
1. The Doppler effect was caused by particles’ Brownian motion, which induce the frequency shiftting of scattered light. Based on the theory of light scattering, the autocorrelation function (ACF) and power spectral density (PSD) were used to characterize the scattered light signal of the particles. The collective diffusion coefficient used to characterize the Brownian motion of the particles was obtained by the scattered light spectrum. The relationship among the collective diffusion coefficient, the particle size and the fluid viscosity were normally characterized by Stokes-Einstein’s expression. Since the hydrodynamic diameter of particle in the suspension is difficult to determine due to various influencing factors, it may lead to unpredictable deviations when the Stokes-Einstein equation is applied directly in the measurement. Therefore, this thesis deduced the Stokes-Einstein equation and introduced the One-Parameter Models to modify the existing DLS measurement principle. Applying the modified measuring principle, the liquid viscosity can be measured directly when the nominal diameter of the particles is given.
2. A new DLS experimental system was established for the viscosity measurement and the requirement of each component was presented in detail. The experiment process and data processing process were presented. Based on the uncertainty analysis, the combinded uncertainty of the new viscosity measurement system was evaluated to be 3.2 % with a level of confidence of 95 % (k=2).
3. Using the DLS liquid viscosity measurement system constructed in this work, the improved measurement principle was experimentally verified. The viscosity of water and ethanol were measured at temperatures from 293.15 K to 333.15 K. Compared with the literature data, the relative deviation is less than 2%, so the feasibility of the improved measurement principle and the reliability of the experimental system were verified. Then the influencing factors of the DLS experiment were analyzed in detail from the aspects of particle and fluid compatibility and particle concentration. It was concluded that the basic principle for selecting particles is to ensure that the particles can be stably dispersed in the fluid to avoid the phenomenon of particle agglomeration or sedimentation and the scattered light signals of the particles can be detected stably.
4. The interaction between the particles in the suspension was analyzed based on the experimental results. The collective translational diffusion coefficient of the particles in the suspension increases with the increase of the particle volume concentration, indicating that the force between the particles in the suspension is repulsive, and vice versa. In addition, it was confirmed that in the ideal thin suspension, the Brownian motion of the particles increases with the temperature increases. The viscosities of bovine serum albumin (BSA) were measured over the concentration of BSA from 20 – 100 mg·ml-1 at interval of 20 and at T = 293.15 K – 313.15 K. The Vogel-Fulcher ＇s function was applied to evaluate the experimental results. The absolute value of the relative deviation between the experimental data and the calculated results is 2.66 %.
Translated Keyword
[Dynamic light scattering, One-parameter model, The interaction between the particles, Viscosity]
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