High performance reversible thermochromic composite films with wide thermochromic range and multiple colors based on micro/nanoencapsulated phase change materials for temperature indicators

The thermochromic films have considerable potentiality in application as temperature sensors. In this work, the reversible thermochromic films with a wide color change temperature range and multiple colors are presented. Two types of thermochromic microcapsules (TCM) and polylactic acid (PLA) were used to prepare a series of reversible thermochromic composite films via the blown film method. The films were thermochromically transformed over the temperature range of 25–50 °C, within which they gradually changed color from green to yellow and colorless. The morphological, thermal, mechanical, thermochromic, and optical properties and thermal cycling durability of the films were subsequently investigated in detail. The results showed that with different mass ratios of blue and yellow thermochromic microcapsules, the films exhibited different colors, while all the films demonstrated a light transmission of over 80% at 750 nm at any temperature. Compared with PLA films, the elongation at break was increased by about 536%. Moreover, the films showed excellent stability even after 60 thermal cycles. Furthermore, the prepared thermochromic composite films were applied to temperature signaling as temperature indication and sensors.