Stable low temperature reversible thermochromic indicators for vaccine storage and transportation.

The thermal properties and stability are key to low temperature reversible thermochromic materials for their application in monitoring the temperatures of vaccine during storage and transportation. In this study, stable low temperature reversible thermochromic indicators (LT-RTIs) suitable for the storage and transportation of temperature-sensitive products were prepared by regulation of the intermolecular interactions in the ternary thermochromic materials (TTMs) via the rational design of components. The thermal stability of low temperature phase transition solvents (PTSs) was correlated to their intermolecular van der Waals force and hydrogen bond interaction to address the volatile issue. The interactions of the PTSs with thermo-sensitive Red and different color developers were analyzed and related to the thermochromic properties of TTMs. It was revealed that thermal-stable PTS together with a strong interaction between the color developer and color former would significantly enhance the stability of TTMs. LT-RTIs with outstanding thermal, thermochromic cycling and low-temperature storage stability displayed two discoloration temperatures at 6 ∼ 8 °C and -23 ∼ -18 °C, enabling temperature indication of OPV and IPV vaccines during storage and transportation.