Intermolecular hydrogen bond and phase change-induced ternary complex for positive/negative reversible thermochromic fabric

Positive/negative thermochromic dyes achieved via hydrogen bond competition. • Adjustable phase change behavior controlled by long alkyl chain integration. • Thermochromic fabrics changed at 47°C (white to red) and 35°C (red to white). Thermochromic ternary complexes relying on phase change materials to switch color currently lack effective measures to regulate their color-changing direction. In this work, a brominated fluorane dye (BDF) was synthesized via condensation reaction and subsequently incorporated with dodecyl gallate (DG, color developer) and 1-tetradecanol (TD, phase change solvent) to form a positive thermochromic ternary complex. The DG participated in the melting and crystallization process of the phase change solvent due to the presence of multiple phenolic hydroxyl groups and long alkyl chains (C12), thereby generating a distinct colorless-to-colored transition upon heating. The positive thermochromic fabric prepared via dip-coating exhibited excellent thermal cycling stability. In contrast, a negative thermochromic complex was constructed with BDF, bisphenol A (BPA, color developer), and TD. Because BPA lacks long alkyl chains to integrate into the phase change process of TD, this negative complex altered its color from red to colorless upon heating. To stabilize the negative thermochromic ternary complex and address phase separation, melamine-urea-formaldehyde (MUF) resin was employed as a protective shell to provide nanoscale spatial confinement for the phase-changing process. The thermochromic capsules (TC) prepared via in situ polymerization exhibited an average diameter of 536 nm, a well-defined core-shell structure, and superior thermochromic reversibility. The reflectance difference of the microcapsules reached approximately 20%, enabling distinct optical color changes. This regulatory mechanism for controlling color-changing direction and stabilizing phase separation through nanoscale confinement effects provides a promising approach for developing high-performance thermochromic textiles. Download: Download high-res image (408KB) Download: Download full-size image