AUC and HDC characterization of heterogeneous polymer dispersions

Particle size distributions with high statistical relevance can be assessed by analytical ultracentrifugation (AUC) and hydrodynamic chromatography (HDC) that are based on fractionation. In this paper, we highlight that these techniques are complementary, showcase failures for spherical colloids that are heterogeneous in diameter and density and report remedies. The AUC with well-known turbidity optics measures particle size distributions in the diameter range 20–3000 nm for typical aqueous polymer dispersions. We report the high-resolution evaluation of AUC turbidity time-scan data, with consistent interdependence of diameter, chemical composition, Mie scattering and concentration. For validation, we retrieve correct diameters and shares in mixtures of known components. The method is then applied to a multimodal adhesive raw product. We find drastic effects on relative shares of components. Finally, we confirm the retrieved diameters with the density-insensitive HDC. This commercial apparatus features moderate fractionation power, short measurement times, high repeatability and <3% accuracy on diameters (20–1200 nm), but the obtained shares are misleading in heterogeneous samples.