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

Using numerical simulation, we study and compare the optical properties of model systems representing three types of scatterer: (a) standard TiO2 pigments, (b) standard TiO2 pigments encapsulated by a hard polymer shell and (c) standard TiO2 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 TiO2 in each system, results show that a standard TiO2 pigment particle encapsulated by air could be a better opacifier than a standard un-encapsulated TiO2 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 TiO2 would only be more efficient than standard TiO2 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.