EFFECT OF PARTICLE-SIZE ON DIFFUSE-REFLECTANCE INFRARED-SPECTRA OF POLYSTYRENE SPHERES

Particle size and its distribution in powdered samples presents potent ial problems for accurate measurement in diffuse reflectance infrared Fourier transform spectrometry. Applications of the Kubelka-Munk theor y to calculate the infrared spectrum from diffuse reflectance data ass umes that the sample is a continuous medium. Particle size is not acco unted for in the transformation. However, powdered samples of the same concentrations but with different particle sizes give different diffu se reflectance spectra. A qualitative interpretation of the effects of particle size on the diffuse reflectance spectra was made by measurin g different concentrations of mixtures of potassium bromide and polyst yrene spheres with defined diameters. Principal component analysis was used to show the differences in the intensities of absorption with pa rticle size variation. Spectral similarity (or dissimilarity) of the p olystyrene spheres as a function of diameter was easy to compare using the score plots of the multivariate data. Additionally, the linearity of the Kubelka-Munk function was tested for three different particle sizes and concentrations. The Kubelka-Munk seems to be linear for lowe r concentrations. Deviation from Kubelka-Munk function starts at an ea rly stage for the smaller particles.