Water-dispersible and stable fluorescent Maya Blue-like pigments

Abstract

Poor water-dispersibility and stability of hydrophobic fluorescent organic pigments (HFOPs) hinder many 5 of their applications. Inspired by the excellent stability of Maya Blue pigments and the water solubility of Laponite RD (LRD), we report facile synthesis of water-dispersible and stable fluorescent Maya Blue-like pigments via the host-guest interaction between LRD and Pigment Red 31 (PR 31), a representative HFOP. The concentration of LRD and solid-state grinding play important roles in effectively dispersing PR 31 into the aqueous solution. The interactions between PR 31 and LRD involve van der Waals, π-π, 10 electrostatic, hydrogen bonding between phenolic hydroxyl groups of PR 31 and silanols of LRD as well as dye-dye hydrophobic interactions. The interactions between PR 31 and LRD occur on the external surface of LRD and the entrance of the micropores of LRD, however, the PR 31 molecules cannot intercalate into the layers of LRD plates. The so-obtained pigments are highly water-dispersible, and very stable to thermal aging and UV irradiation owing to the interactions between LRD and PR 31, and the 15 shielding effect of LRD.

Hybrid Pigments from Anthocyanin Analogues and Synthetic Clay Minerals

“… 30 − 32 Hybrid materials prepared from organic dyes and laponite have attractive colors and stability reminiscent of those of the ancient Maya Blue pigment. 20 , 33 …”

“…Laponite is a synthetic hectorite-type clay mineral consisting of two tetrahedral silicate layers connected to an octahedral Mg 2+ layer via oxygen atoms. − Its highly expansible structure is described as strongly anisotropic platelets or disks that can be exfoliated in an aqueous medium in low concentrations. − The average size of the individual laponite particles is approximately 25 nm in diameter and 0.92 nm in thickness. ,, The net negative charge on the faces of these disks are due to isomorphous substitutions of Mg 2+ by Li + in the octahedral layer and is compensated by exchangeable hydrated cations such as Na + in the interlayer space between the faces. − On the edges of the platelets, the charge can vary due to the presence of amphoteric SiOH and/or MgOH sites with pH-dependent charges. − SYn-1, on the other hand, is a synthetic 2:1 phyllosilicate that possesses random layering of expandable and nonexpandable dioctahedral layers in a 1–2 ratio. − The layers of SYn-1 present negative charges due to partial isomorphous substitutions of higher valence cations by lower valence cations of similar size, as for example replacement of Si 4+ by Al 3+ in the tetrahedral sheets . The external surface sites and those in the expandable layers participate in cation exchange and can therefore host cationic molecules. , Despite the presence of expandable layers, compared to laponite, SYn-1 is essentially a nonswelling clay. , The adsorption of dyes on SYn-1 has been shown to produce promising hybrid materials with interesting luminescence and aggregation properties. − Hybrid materials prepared from organic dyes and laponite have attractive colors and stability reminiscent of those of the ancient Maya Blue pigment. , …”