Measurement of orientation distributions of spheroidal particles by light scattering
Abstract
The problem of determination of the orientation distribution by light scattering for an arbitrarily oriented population of Rayleigh-Debye-Gans spheroids has been solved. The solution is based on the conditions of single and independent scattering from nonabsorbing monodisperse spheroids. An algorithm and method, which incorporate a constrained quadratic optimization, have been developed to estimate the orientation distribution function from scattered intensity measure in two dimensions ($\theta$ and $\phi$). The effects of the distribution shape, initial orientation, particle size, and shape on the performance of the inverse algorithm have been elucidated. Because the direct intensity expression was inverted, the orientation distribution functions can be generally estimated precisely over the entire angular range from data obtained over a finite range with error-free simulated data. These results show the power of this approach. The reduction in precision of the estimated orientation distribution which results from experimental error and polydispersity in volume has been considered and shown to be minimal. An instrument has been designed and constructed to measure scattered light intensities as a function of $\theta$ and $\phi$. Monodisperse microspheroids were prepared for use as model particles. Measured intensity data are presented for spheres and oriented spheroids. Furthermore, the spheroid intensity data were utilized to estimate the orientation distribution. Excellent agreement between the estimated distribution and the known distribution was seen. A theoretical expression has been derived for the turbidity from populations of RDG spheroids. This derivation is also based on single and independent scattering from nonabsorbing monodisperse spheroids. Some orientation information is lost because of the coupling between the incident beam polarization and the form factor, which contains all of the orientation information. Also, a general technique for determining the orientation distribution has been developed, using the previously derived expression. Through use of coordinate rotations, the lost orientation information is recovered. Estimation of the entire distribution requires spectroturbidimetry data for many different incident beam directions or sample positions.
Degree
Ph.D.
Advisors
Franses, Purdue University.
Subject Area
Chemical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.