Color Tuning of an Acidic Blue Dye by Intercalation into the Basic Interlayer Galleries of a Poly(allylamine)/Synthetic Fluoromica Nanocomposite

The intercalation of an acidic blue dye, Brilliant Blue FCF, into poly(allylamine) (PAA)/synthetic fluoromica (Na-TSM) was investigated as a function of the reaction pH (1.5-12.0) and the loading of the polyelectrolyte and acidic dye. Surprisingly, the colored solids so obtained show a variety of colors from the original blue to yellow through green with only a slight increase in the reaction pH. At low and neutral pH (1.5-9.5), the acidic blue dye molecules were adsorbed/intercalated on/in PAA/Na-TSM mainly through electrostatic interactions between protonated amine groups on the PAA chains and sulfonate groups of the dye, resulting in the original blue color. UV-visible spectroscopic data hint that the adsorbed/ intercalated dye molecules were aggregated. The color shifted to blue-green at pH 10.0 and finally to yellow at pH 12.0. At high pH, the PAA layers have lower charge density and the dye is well-dispersed within the interlayer galleries. The fraction of neutral primary amine groups increases with increasing reaction pH, and interaction of the neutral amine groups to the dye becomes the dominant driving force for intercalation. On the basis of these intercalation results at different pH and some control experiments, the pH-dependent color change of the intercalated dye appears to be caused by inhibition of the intramolecular interaction between N+ in the dye conjugated system and a free sulfonate group.