Title : In situ structural modification and drying of pigment particles PI :

Pigments are widely-used commercial additives to impart color to inks, plastics, coatings and cosmetics. Being insoluble in the dispersing medium, compatibilization of pigments is essential to form stable pigment dispersions. This is achieved through the use of surfactants. The pigment particles display a multi-level hierarchical structure composed of primary particles on the nanoscale, a size too small to effectively scatter light, that are clustered into aggregates of about 10 to 100 nm in size.[1] Our recent work demonstrated that the size and density of these aggregates depends partly on the primary particle size and the surface interaction between particles in the carrier medium moderated by the surfactant.[2] For organic pigments the primary particles are solid clusters of elemental single crystals whose size depends on the quality of the surfactant/solvent/pigment interface. For these colloidal systems, we mapped out the thermodynamics of reversible aggregation using a new theory proposed by Vogtt.[3] We discovered that the affinity of the surfactant for the pigment crystallite surface increased as its solubility decreased with temperature (LCST behavior) by demonstrating a change in primary particle and aggregate size with temperature using USAXS / SAXS / WAXS as shown in Figure 1. The pigment particles collapsed and precipitated at the phase separation temperature of the surfactant also shown in Figure 1 (supporting document).