Particle Size Distribution of SBR and NBR Latexes by UV-VIS Turbidimetry near the Rayleigh Region

Abstract

Abstract This paper deals with data treatment problems that arise when turbidimetry is employed to estimate the particle size distribution (PSD) of soft polymer latexes with low diameter limits around 40 nm. Scanning electron microscopy and dynamic light scattering were used as comparison techniques. Industrial latexes of styrene-butadiene rubber (SBR) and of acrylonitrile-butadiene rubber (NBR) were investigated. The data treatment involved the use of Mie's Model to obtain an average diameter and/or the complete PSD. For estimating the complete PSD, a least squares optimization (with an imposed distribution shape) and a numerical deconvolution procedure (without assumptions on the distribution shape) were attempted. A synthetic example was solved to investigate the limits of the applied numerical methods. For the polymer refractive index functions, Cauchy's Law was used — and its adequate adjustment proved essential for good turbidimetric estimations. A reasonable agreement between the turbidity measurements and the other independent estimations was verified. For the SEM observations, the soft latexes were hardened by irradiation before observation, but negligible diameter variations were detected.