New pigments based on carminic acid and smectites: A molecular investigation

Abstract

Hybrid materials based on montmorillonite, a cationic polymer and carminic acid were prepared. The surface charge of montmorillonite was inversed thanks to the cationic polymer, polydiallyldimethylammonium chloride. Samples were characterized by a set of different techniques including Infrared (IR) and Nuclear Magnetic Resonance (NMR) spectroscopies to highlight the nature of the interactions between the organic and inorganic parts. The photo-stability of the samples was tested for different durations, and L*a*b* parameters were measured. It was possible to propose an approach for the degradation mechanism of the supported dye thanks to EPR (electron paramagnetic resonance) spectroscopy. The experimental data were in agreement with the theoretical periodic DFT calculations where a molecular scheme of the adsorption complex was proposed, and the importance of hydration on the stability of the adsorption complex highlighted.