DETERMINATION OF THE PARTICLE SIZE DISTRIBUTION IN POLYMER LATEX USING QUASIELASTIC LIGHT SCATTERING AND DIELECTRIC SPECTROSCOPY.

摘要

Methods of assessing the particle size distribution of submicron particles are reviewed, with a focus on their potential as on-line measurements. Quasielastic light scattering (QLS) was selected for further experimental investigation. A novel method using dielectric spectroscopy is also considered.;Analysis of QLS data to determine the particle size distribution is not difficult when the distribution is monodisperse but the analysis is more complex when the distribution is polydisperse. Several methods of analysis for polydisperse particle size or molecular weight are reviewed. These methods' comparative performance on sets of simulated and experimental data from unimodal and bimodal, broad and narrow distributions is evaluated.;Two of the better methods, constrained regularization and Non-Negative Least Squares (NNLS) are extended to include the Mie scattering factor; it follows that the resulting particle size distribution is based on mass rather than on relative intensity scattered by each particle size. QLS data collected at several scattering angles and correlation sample times is used to determine the structure of the particle size distribution.;The dielectric spectrum of polymer latex is sensitive to particle size. In particular, the critical frequency, where the imaginary part of dielectric permittivity is maximal, is inversely proportional to the square of the particle radius. The literature on dielectric measurement of polymer molecules in aqueous or non-aqueous solution and colloidal suspensions is reviewed. One of the modern theories explaining the dielectric enhancement phenomenon in colloidal suspensions is used for a simulation study. An instrument capable of quickly measuring the spectra of relatively highly conductive polymer latex is designed, built and tested; the instrument uses a four electrode cell and a frequency multiplex technique. Testing indicates that the instrument accurately measures the spectra of synthetic circuits. However, lead capacitance becomes a more severe problem when measuring latex samples. Further modification of the instrument is recommended to minimize the lead capacitance problem.