Sensitive Colored Hybrid Inorganic/Organic Pigments Based on Polymer-Coated Microsized Particles

Abstract

We present herein the preparation of colored hybrid organic/inorganic pigments: poly(styrene- co-alizarin)/mica. We have used direct nitroxide-mediated radical polymerization of styrene and modified alizarin from mica-bound bicationic azo compounds as initiator. The color of the P(S-co-A)-mica composites is related both to the adsorption density of polymers on mica surface and to the length of the macromolecular chains. The longer the polymerization time is, the more the chains are crushed onto the mica surface and the nearer the dye is to the surface. Consequently, the dye will be strongly influenced by the oxanions of the surface leading to color variation. This variation has been attributed to the superimposition of different adsorption of the alizarin due to different states: when closer to the surface, alizarin is more influenced by oxanions and its color tends to pink, when farther away from the surface, the alizarin electronic state is less changed and its color tends to yellow. Finally, the global color is due to the mix of the different electronic states leading to orange pigments. This behavior could be represented as a gradient of alizarin position from the mica surface to the air/polymer interfaces. Depending on the synthesis methodology, the color of such pigments can be easily tuned not only by adjustment of the length and the grafting density but also by the number of dyes in the chains.