The reversible thermochromic fabric for the double-stage temperature monitoring

The three-component thermochromic materials have been widely used for temperature monitoring due to abundant colors and thermochromic temperatures. Nevertheless, there are still limitations in depicting broader temperature variations. So we propose to construct a double-stage thermochromic response strategy. We synthesize thermochromic microcapsules with dual thermochromic temperatures by in situ polymerization using melamine–formaldehyde (MF) resin as the encapsulating shell. The thermochromic microcapsules exhibit color changes from pink or blue to white under the control of 6′-(Diethylamino)-1′,3′-dimethylfluoran (DDF) and the crystal violet lactone (CVL), respectively. Furthermore, the thermochromic microcapsules exhibit exceptional thermal properties and possess a uniform spherical morphology. Simultaneously, a double-stage thermochromic fabric is produced using screen printing techniques in order to track variations in the surrounding temperature. The double-stage thermochromic fabric has the ability to alter its color state at 25 °C and 35 °C and further divide the temperature range into four segments: below 20 °C, 20 °C–25 °C, 25–35 °C, and above 35 °C. More interestingly, the double-stage thermochromic fabric still retains the thermochromic property even after being heated and cooled 25 times or immersed in various organic solvents for 24 h. This remarkable characteristic of the double-stage thermochromic fabric offers a promising avenue for temperature display across a wide range.