Preparation of hydrophobic layered double hydroxide-based composite pigments via octyltriethoxysilane surface modification for cosmetic applications

Abstract

Pigments play a pivotal role in the cosmetic industry, in which the development of pigments with concurrent color diversity, hydrophobicity, biocompatibility and photostability remains a great challenge. Herein, we report organic–inorganic composite pigments synthesized via a combination of organic dye anions (Ponceau SX and acid green (AG)), layered double hydroxides (LDHs) and octyltriethoxysilane (OTEOS) (denoted as O/Dye-LDHs: O/SX-LDHs and O/AG-LDHs).The prepared composite pigments were characterized via a comprehensive investigation based on X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS-mapping), Fourier transform infrared (FT-IR) spectroscopy, CIE 1976 L*a*b* color scales, static contact angle measurement and HET-CAM assay. The results confirm the successful intercalation of organic dye anions into the interlayer region of LDHs via host–guest interactions and the surface modification of OTEOS on the layer surface, forming a new kind of hydrophobic organic–inorganic composite pigment with a sandwich structure. LDH layer protection and OTEOS coating play crucial roles in the high photostability, good hydrophobicity and satisfactory biocompatibility of pigments. In addition, O/Dye-LDHs exhibit rich color and color adjustability. Impressively, we applied mixture composite pigments with different O/SX-LDH-to-O/AG-LDH ratios to formulate an eye shadow cream, which present a series of popular and natural colours with water resistance to enhance one's attractiveness and appearance. This work provides a promising strategy for the design of safe and efficient composite pigments, demonstrating their potential application in the field of makeup.