Multiple Scattering Correlation Measurements in Fluid/particle Suspensions: Application to Particle Characterization

Scope and method of study. The purpose of this study was to examine different parameters such as transmission, back-scattering, off angle detection, polarization, and different ranges of optical thickness (low to high), in dynamic light scattering measurements from multiple scattering fluid/particle suspensions. In addition, the validity of correlation transfer (CT) theory was investigated and a methodology was provided for finding micron size spherical particle diameter. The experiment has been setup using an Argon-Ion laser, PMT, goiniometer, mirrors, lenses, and beam splitter. Solutions of 0.3 m latex particles mixed with water have been used as the test samples. The measurements have been compared to CT theory using exact and approximate numerical solutions. Findings and conclusions. It was found that the two-dimensional correlation function decays slower as compared to the one-dimensional situation. The correlation function decays faster as effective optical thickness increases. Polarization affects the back-scattering correlation function decay rate for all optical thicknesses, while it may be unimportant for transmission at high optical thicknesses. Transition from single scattering to multiple scattering appears to begin around an optical thickness of 0.05. In addition, the correlation function appears relatively insensitive to off angle detection for effective optical thicknesses of 3 or greater transmission and 1.5 or greater for back -scattering. However, for smaller optical thicknesses, the correlation function appears to be dependent on detection angle. The CT theory has demonstrated promise as a model to bridge the gap from single scattering to multiple scattering correlation. A methodology is proposed herein to allow the determination of particle size using data to match CT predictions, as long as two index of refraction changes at the boundaries and a realistic single scattering phase function are considered in the numerical results. A method of improving the classical P_{rm N}~imation is presented and compared to the exact solution using a 3-term Legendre polynomial single scattering g^1 expansion. Satisfactory agreement is achieved.