Advanced Particle Size Analysis in High-Solid-Content Polymer Dispersions Using Photon Density Wave Spectroscopy

Abstract

High-solid-content polystyrene and polyvinyl acetate dispersions of polymer particles with a 50 nm to 500 nm mean particle diameter and 12–55% (w/w) solid content have been produced via emulsion polymerization and characterized regarding their optical and physical properties. Both systems have been analyzed with common particle-size-measuring techniques like dynamic light scattering (DLS) and static light scattering (SLS) and compared to inline particle size distribution (PSD) measurements via photon density wave (PDW) spectroscopy in undiluted samples. It is shown that particle size measurements of undiluted polystyrene dispersions are in good agreement between analysis methods. However, for polyvinyl acetate particles, size determination is challenging due to bound water in the produced polymer. For the first time, water-swelling factors were determined via an iterative approach of PDW spectroscopy error (Χ2) minimization. It is shown that water-swollen particles can be analyzed in high-solid-content solutions and their physical properties can be assumed to determine the refractive index, density, and volume fraction in dispersion. It was found that assumed water swelling improved the reduced scattering coefficient fit by PDW spectroscopy by up to ten times and particle size determination was refined and enabled. Particle size analysis of the water-swollen particles agreed well with offline-based state-of-the-art techniques.

Critical Review of Techniques for Food Emulsion Characterization

“…It can measure light scattering, and absorption by emulsion droplets, or droplet/particle size. The primary requirement for effective measurement is that the sample should exhibit ample light scattering (with a reduced scattering coefficient µ s' > 0.05 mm −1 ) and that the absorption of the sample should be markedly lower than the scattering (the absorption coefficient µ a << µ s' ) [188]. As UV-Vis or IR spectroscopy measures the absorbance, the important feature of PDW spectroscopy is that it allows the measurement of absorption and scattering properties of turbid materials independently, without calibration [189].…”