光散乱法によるポリスチレン粒子の直径の精密測定

Abstract

Polystyrene latex particles are used generally for calibration of particle size analyzers and electron microscopes, and also for an experiment to verify the light scattering theory, because the particles have excellent characteristics in sphericity and monosize distribution. It is of great importance, therefore, to measure precisely the diameter of the polystyrene particles. This paper describes a light scattering method to measure the particle size, because the method permits an absolute measurement and allow to measure it without any contamination and/or destruction of particles. In this method, the size of suspended particles was determined by fitting theoretical values based on Mie scattering to experimental data for an angular distribution of the intensity of light scattered from particles. A laser scattering photometer used in the experiment has the constitutional features that are insensitive to variation of the intensity of light source (He-Ne laser, 633nm) in measurements of scattered light intensity and to nonlinearity in a photoelectrical detection system, since the photometer adopts a new system of measurement on the basis of a principle of zero method. Light scattering measurements were made for suspensions of 0.9μm particles of the SRM of NIST and 2μm particles. The result for the 0.9μm particles agrees with the value of NIST within 0.3% in the number average particle diameter. The coefficient of variation of repeated measurements are 0.5% for the 0.9μm particles and 0.15% for the 2μm particles. The best fits of measured values for an angular distribution of the scattered light intensity to the theoretical values are within 5% at the scattering angle between 4° and 38°. The experimental results prove good accuracy and usefulness in measurements attained for the polystyrene particles by the laser scattering photometer developed in this work.