The Use of an Exact Light-Scattering Theory for Spheroidal TiO2 Pigment Particles

• Published in: Particle & particle systems characterization 2006-08, Vol.23 (2), p.159-164
• Main Author: Jalava, Juho-Pertti
• Format: Article
• Language: English
• Subjects: light scattering; optical properties; particle size; process and quality control; titanium dioxide
• ISSN: 0934-0866; 1521-4117
• DOI: 10.1002/ppsc.200601025

Titanium dioxide pigments are widely used, e.g., in paints, printing inks, plastics, and papers, because of the excellent and whiteness they provide. As is well known, the opacity and to it related optical properties depend on the pigment's crystal‐ and particle‐size distributions (CSD, PSD). Therefore, the process and quality control of the CSD and PSD are very essential. The development of a straightforward and sophisticated method for process and quality control is presented here. The principal component is a new determination method for the PSD based on an accurate theory of light scattering of spheroidal particles. In this new method, called the turbidity spectrum method (TSM), the whole turbidity spectrum is measured. This spectrum, which is due to the particle‐size distribution of the pigment particles, is then solved using the T‐matrix method by taking into account the shape of the particles. After that the CSD is extracted from the PSD. The T‐matrix method is one of the most powerful and widely used tools for the rigorous computing of electromagnetic scattering by non‐spherical particles. The repeatability of the mean PSD (∼200 nm) obtained by the TSM is excellent, with a standard deviation of 0.1 nm (0.05 %). Linear regression models based on TSM results were developed for undertone and tint‐reducing power, which are important optical parameters of the pigment. The excellent repeatability of the TSM results was necessary for the production of representative models. A new method for process and quality control by measuring crystal and particle size distributions is presented. The so‐called turbidity spectrum method measures the whole turbidity spectrum which is then evaluated using a T‐Matrix calculation of light scattering by spheroidal particles. An excellent repeatability of the measurements is shown.