Reversible thermochromic behavior and mechanism of Congo red/palygorskite nanohybrid induced by mechanochromism

• DOI: 10.1007/s10934-021-01158-1
• Publication Date: 2021-09-29T18:11:24Z
• Authors: Hao Chen; Yanxian Jin; Aiguo Zhong; Junyong Wu; Hua Yan; Rongrong Li
• Keywords: 02 engineering and technology; 0210 nano-technology

To better understand the effect of the interaction of dye molecules at the interface of clays on thermochromism, we report here a new preparation strategy for a clay-based reversible thermochromic material, namely a nanohybrid prepared by heavily grinding the Congo red dye with palygorskite. Firstly, the hybrid was prepared by liquid-phase adsorption–desorption method in an acidic system with a pH less than 3.5. The color of the hybrid changed from blue to red through heavy grinding, which is mainly due to such a process producing some Si–O− broken bonds, which capture H+ ions in the protonated dye molecule, thus transforming it from the ammonium and azonium forms to the neutral form, leading to color change. Furthermore, the color of the heavily ground hybrid changed from red to purple after heating, the transition point being around 110 °C. This is mainly due to the fact that both adsorbed and zeolitic water in palygorskite were removed by temperature rise. These two kinds of water can interact with the dye molecules by hydrogen bonding, the destruction of which leads to the change of the balance between the different forms of dye molecules in the hybrid, further affecting the color. The reversible desorption and adsorption of the two kinds of waters determines the reversibility of the thermochromic property in the heavily ground hybrid. A polyvinyl alcohol film prepared with the pigment exhibited an excellent thermochromic property changing color (from red to purple) at 110 °C; and no significant change in performance was observed after repeated use 30 times. This clay-based hybrid can be used as a thermochromic pigment, e.g., in the sterilization of food and medical equipment, the preparation of intelligent tires and other related fields.