非対称フロー場分級法によるナノメートルからマイクロメートルまでの様々なシリカ系材料のサイズ評価

Silica materials vary widely in size, structure, and applicability, making their accurate characterization essential for ensuring proper performance across research and industrial applications. A strategy for hydrodynamic size assessment of silica materials ranging nanometers to micrometers is proposed here. Silica nanoparticles (SiO₂NPs) of different sizes, halloysite as silica nanotubes, and silica obtained from rice straw combustion residues have been characterized employing asymmetrical flow field flow fractionation technique in combination with a DLS detector (AF4-DLS). Additional analyses were performed using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and batch-mode DLS.

Firstly, the different silica materials were dispersed using alkaline treatment. For halloysite, a detailed dispersibility assay was performed using a wide variety of compounds to identify optimal conditions for stable suspensions. The sizes of SiO₂NPs obtained by AF4-DLS ranged between 15 and 200 nm, according to the type of NPs and their aggregation state. Halloysite exhibited sizes around 240-280 nm, corresponding to the transversal length. Additionally, the functionalization of this material with pigments was evaluated. As an example of micro material, silica extracted from combustion residues of rice straw was studied, resulting in average hydrodynamic diameters reaching up to 4 μm. Finally, analytical parameters were evaluated, and the results demonstrated suitable precision values, with limit of detection (LOD) in the range of 1.5∙10^-4 % (w/v) to 7.2∙10^-4 % (w/v).

These findings demonstrate the utility of the proposed AF4-DLS analytical strategy as an effective tool for silica characterization. By enabling assessment of hydrodynamic size across nanometer to micrometer scales, this approach enhances the understanding of particle behavior, aggregation, and functionalization, thereby supporting more informed decisions in the design and applications of silica materials.