A urea-modified polydiacetylene-based high temperature reversible thermochromic sensor: Characterisation and evaluation of properties as a function of temperature

- Modification of PCDA with urea improved thermal & thermochromic properties.
- Introduction of reversible thermochromism was achieved.
- Temperature sensor was reversible up to 150 °C (pcd-urea) from just ∼60 °C (PCDA).
- Clearly distinguishable colour patterns of sensor represented temperature ranges.
- Pcd-urea thermal properties/behaviour competes with the best reported in literature.

Modification of polydiacetylene (PDA) with a small compound capable of forming multiple hydrogen bonds resulted in new and improved qualities such as high-temperature reversible thermochromism and higher melting temperature. Several distinct colours were exhibited to indicate different temperatures. Polydiacetylenes often suffer from irreversible thermochromic transitions and that limits their applicability in sensor development. A simple thermochromic PDA sensor that exhibits reversible thermochromism up to 150 °C is reported. This was achieved by introducing urea to the head group of 10,12-pentacosadiynoic acid (PCDA) and shining 254 nm UV light to the resulting fine powders to form a deep-blue-coloured poly-pcd-urea. Thermochromic and thermal properties of the PDA were investigated using ultraviolet-visible (UV-vis) and X-ray diffraction (XRD) spectroscopic techniques; and thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. UV-vis studies revealed that poly-pcd-urea returned to its original blue colour when it was heated up to 150 °C. DSC and XRD revealed that the reason for loss of reversibility was probably because poly-pcd-urea melted at 151 °C and upon solidifying did not fully recover the crystalline structure responsible for its blue colour. TG analysis showed that the polymer was thermally stable up to 315 °C.