Quantitative characterization of aggregated and agglomerated titanium dioxide nanomaterials by transmission electron microscopy

• The physical properties of four TiO2 nanomaterials are determined quantitatively.
• Size and shape distributions are determined by TEM imaging and semi-automatic analysis.
• Number-based distributions are compared by iterative curve fitting.
• The type of vial (glass or PP) used for preparation of dispersions alters the pH.
• The changes in pH influence the stability and polydispersity of the nanomaterials.

The physical properties of TiO2 nanomaterials are determined quantitatively using a method that combines imaging by transmission electron microscopy (TEM) with semi-automatic particle detection and analysis. The method is applied on four powdered TiO2 nanomaterials, NM-102, NM-103, NM-104 and NM-105, dispersed in distilled water.Qualitative analysis shows that the stability and polydispersity of the dispersed nanomaterials are influenced by the material from which the vial used for dispersion, is made. In glass vials, the uncoated nanomaterials, NM-102 and NM-105, precipitate immediately after sonication, while the coated nanomaterials, NM-103 and NM-104, remain stable in dispersion. In polypropylene vials, stable dispersions are obtained for all nanomaterials. It is shown that the vial material alters the pH of the dispersions, which in turn influences the agglomeration state of the nanomaterials.Quantitative analysis of stable dispersions, based on TEM imaging combined with semi-automatic image analysis, results in number-based distributions of characteristic parameters, measuring the size, shape and surface topology of the unbound, aggregated and agglomerated TiO2 particles. Iterative curve fitting is applied to the number-based distributions of selected parameters and allows objective comparison of the distributions based on the properties of the fitted curves. Using this method, it is shown that the size, the shape and the surface properties of NM-102 and NM-105 and of the coated nanomaterials, NM-103 and NM-104, are significantly different. The physical characteristics of NM-103 and NM-104 are similar. This supports the validity of the method as these are in fact the same material with a different coating.

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