A new durable pigment with hydrophobic surface based on natural nanotubes and indigo: Interactions and stability

Covering with polyorganosilane (POS) was proved as an effective way to enhance the chemical and thermal stability of clay/dye hybrid pigments. But the photostability and interactions with clay minerals, dyes and POS layer has never been reported. In order to investigate above issues, new organic-inorganic hybrid pigments based on halloysite (Hal) and indigo (In) were prepared by grinding method. X-ray diffraction, transmission electron microscopy, thermogravimetry, Fourier transform infrared spectroscopy were applied to characterize the structure of In-Hal (without POS layer) and In-Hal-POS (with POS layer) pigments. Solid state nuclear magnetic resonance (NMR) was employed to reveal the interactions between Hal, In and POS. Reflection spectra and CIE 1976 color space system were used to evaluate the color parameters and color changes of pigments. Thermal stability, chemical resistance to ethanol, 1 mol·L^-1 HCl and 1 mol⋅L^-1 NaOH, and light fastness to visible light were tested. Indigo molecules dispersed on the surface of Hal nanotubes. POS layer homogeneously covered on the surface of hybrid pigments, without changing the crystal structure and morphology of Hal. Covering with POS layer seldomly affect the color of hybrid pigments. However, In-Hal-POS exhibited better stability than In-Hal, due to hydrophobic surface which can prevent indigo molecules from chemical reactions and degradation. A new route was proposed to prepare organic-inorganic hybrid pigments, ignoring the interaction between dye molecules and substrates.

Highly fluorescent hybrid pigments from anthocyanin- and red wine pyranoanthocyanin-analogs adsorbed on sepiolite clay

Flavylium cations serve as models for the chemical and photochemical reactivity of anthocyanins, the natural plant pigment responsible for many of the red, blue and purple colors of fruits and flowers. Likewise, pyranoflavylium cations serve as models of the fundamental chromophoric moiety of pyranoanthocyanins, molecules that can form from reactions of grape anthocyanins in red wines during their maturation. In the present work, hybrid pigments are prepared by the adsorption of a series of five synthetic flavylium cations (FL) and five synthetic pyranoflavylium cations (PFL) on sepiolite clay (SEP). The FL are smaller in size than the PFL, but both can in principle fit into the tunnels and/or external grooves (with dimensions of 3.7 × 10.6 Å) of SEP. Measurements of the fluorescence quantum yields of the adsorbed dyes indicate that they are at least as fluorescent as in acidic acetonitrile solution, and in a few cases substantially more fluorescent. The observation of biexponential fluorescence decays is consistent with emission from dye molecules adsorbed at two distinct sites, presumably tunnels and grooves. These hybrid materials also have improved properties in terms of stability of the color in contact with pH 10 aqueous solution and resistance to thermal degradation of the dye. SEP thus appears to be a promising substrate for the development of highly fluorescent flavylium or pyranoflavylium cation-derived hybrid pigments with improved color and thermal stability.

Ethanol–NaOH solidification method to intensify chitosan/poly(vinyl alcohol)/attapulgite composite film

Chitosan/poly(vinyl alcohol) (CS/PVA) films have recently attracted considerable attention.