Theoretical analysis of light scattering properties of encapsulated rutile titanium dioxide pigments in dependent light scattering regime

Abstract Using numerical simulation, we study and compare the optical properties of model systems representing three types of scatterer: (a) standard TiO 2 pigments, (b) standard TiO 2 pigments encapsulated by a hard polymer shell and (c) standard TiO 2 pigments encapsulated by a layer of air and a polymer shell. Calculations are performed taking into account multiple and dependent light scattering regimes. Assuming an equivalent amount of TiO 2 in each system, results show that a standard TiO 2 pigment particle encapsulated by air could be a better opacifier than a standard un-encapsulated TiO 2 pigment because the presence of air could provide: (a) additional volume to the existing particle to scatter light; (b) better redistribution of the scattered field in the backward hemisphere; (c) a scattering cross-section less affected by crowding and (d) spacing effects due to the presence of the thin hard polymer shell which is required to encapsulate the air layer. Nonetheless, results also suggest that such benefits could probably not be exploited in real paint systems as encapsulated TiO 2 would only be more efficient than standard TiO 2 in a range of pigment volume filling fractions (PVC) that would not generate enough scattering efficiency to yield complete hiding as required by international standards.