An experimental study of particle sizing in static condition and in shear flow by diffusing-wave spectroscopy

• Main Author: Huang, Huan
• Other Authors: Zhang, Xiaoxian
• Published: University of Liverpool 2012
• Subjects: 620
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.564259

This thesis focuses on the micro/nanoparticle size measurement by using Diffusing-wave Spectroscopy, investigating the laser power and concentration effect on the measurement and researching the measuring method for particles in shear flow. A DWS-CCD backscattering experiment set-up was used in this project. By using this set-up, in all about 2000 experiments were performed during the project, including system testing, laser power influence study, concentration effect study and shear flow study. In the beginning, a detailed analysis of the particle sizing for particles in static condition was carried out by summarising the principles and procedures. The results revealed that the experimental set-up in this work was reliable and repeatable. A calibration process was still required for the CCD’s frame rate and resolution, the light absorption and the CCD’s position in the set-up. After determining some important parameters, the research was extended to laser power and concentration influence study. The autocorrelation functions were produced under different laser power and for different concentration of particle solution. Analysis confirmed the influences, and the results were expressed in formulas to describe specific effects for laser power and solution concentration. Based on the formulas, new equations for particle sizing were derived for different concentration ranges. After that, particle’s motion and light scattering in shear flow were investigated. It was concluded that three regions could be used to describe the particle’s movement under shear force; in different regions, the autocorrelation functions were different due to the variation of the characteristic time scales. The Brownian motion and shear strain dominated particle’s movement under specific flow velocities. Therefore, for particles subjected to high flow velocities, a new particle sizing formula was produced to distinguish the general formula which was only valid for particles under Brownian motion. Contributions made by this research are applying DWS application to micro/nanoparticle sizing in different conditions. In static condition, the laser power and concentration influence were described in formulas; new equations were produced for particle sizing for different concentration range. In shear flow, the thresholds of Brownian motion domination and shear flow domination were found; a new particle sizing equation was derived for particles only controlled by shear force.