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Study on Measurement of Nanoparticle in Concentrated Dispersion Based on Backscattering Dynamic Light

Author: YangZuo
Tutor: ZhengGang
School: University of Shanghai for Science and Technology
Course: Optical Engineering
Keywords: concentrated nanoparticle dispersion particle sizing backscattering dynamic light modern power spectrum estimation
Type: PhD thesis
Year: 2009
Downloads: 180
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As one of the important subjects in the21st century, nanotechnology has broughtmaterials science extensive and profound changes. Our country has identified"nanotechnology research" as one of the four major scientific research programs in theoutline of development planning, which was announced in medium and long-termNational Science and Technology in9th Feb.2006. Nanoparticle sizing is extremelyimportant in nano-technology. Especially in recent years, with the nano-technologywidely used in pharmaceutical, biotechnology, electronics, optoelectronics, energy,catalytic and ceramic and other fields, the requirements of various industries for themeasurement and monitoring of nanoparticle are increasingly stringent. And itsdevelopment level has become a standard to measure the level of a NationalNanotechnology and overall strength in this area. Compared with advanced countries,Our country has a distance in the nanoparticle sizing techniques and equipment,particularly in the measurement of nano-particle size in concentrated dispersion.Dynamic light scattering (DLS) technique is the most widely used nano-particlesizing technique currently. However, the traditional dynamic light scattering method isgenerally applied only to the measurement in dilute dispersion. In this paper, a methodwas proposed to solve the difficulty of the measurement of nanoparticle in concentrateddispersion, which was based on backscattering dynamic light, as well as themeasurement by dynamic light scattering spectrum based on the modern powerspectrum estimation.The main researches are as following:The factors, which limit the measurement by traditional DLS in concentrateddispersion, are studied. It was proposed that the focus should be first put on theelimination of the multiple scattering effect, when measuring the nanoparticle inconcentrated dispersion. And a review on research status at home and abroad wasanalyzed for this difficulty. Finally the method and equipment for nanoparticle sizingbased on backscattering dynamic light in concentrated dispersion was developed.Starting from the Maxwell’s equations, the expressions of the general equation ofthe scattered light based on the fluctuation of the signal were derived. According to thestatistical properties of particles with Brownian motion, the characterization method ofthe intensity fluctuation of scattering light was studied, and the expressions of the particle size related to the fluctuation of the signal were set up.The relationship between the particle size and the spectrum density of scatteredlight field was set up, using the characteristic function of particle movement and that itis a double Fourier transform in time and space between the scattering spectra based onthe model of the movement of particle and characteristic function of movement.The development and existence of the problems of dynamic light scatteringspectrum measurement technique were studied. A new method was proposed based onthe modern power spectrum estimation. From the counting statistical characteristics ofthe Photomultiplier tubes, the spectral density expression of the intensity of scatteringlight was deduced by converting the time-domain auto-correlation function to frequencydomain power spectral density according to Wiener-Khintchine theorem; The powerspectral density estimation of the dynamic scattering light was implemented by the useof autoregressive (AR) model of modern power spectrum estimation with FFT; Finallythe problem that the number of p-order could not be determined because of theunknown particle size in application was resolved by calculating the rank of the matrixof signal auto-correlation.The measurement system for nanoparticle sizing in concentrated dispersion wasdeveloped based on backscattering dynamic light scattering, which includes: preparationof test nanoparticle dispersion, optical system (the selection of light source, the incidentand scattering optical path), the devices for signal detecting and treatment (the digitalcorrelator and photon counter were used separately based on two methods of signalanalysis). The experiments were carried out by correlation spectroscopy in time-domainand spectral density in frequency domain separately, and the results were compared andanalyzed with the measurements using traditional photon correlation spectroscopy.A number of problems about the practical application of measurement werediscussed, which includes: The impact of the measurement result from the changes ofthe Polarization of light source; the change in measurement results led by the samplingtime, as well as the problem of the best detection aperture in traditional dynamic lightscattering system.

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