Reversible halochromic PLA film for naked-eye detection at the extreme base condition

Abstract

ABSTRACT Exposure to extreme base conditions in indoor environments may lead to adverse health effects on living beings. Proper ventilation and real-time detection are very important upon exposure. A simple and highly sensitive reversible base sensor is successfully prepared for real-time detection of the extreme base condition of aqueous base analytes. Halochromic poly lactid acid (PLA) pH film sensor containing thymolphthalein (THY) dye and polyethylene glycol (PEG) was developed by solution casting method. To increase the effectiveness of PLA pH film capabilities as a base sensor, the impact of altering the concentration of THY and PEG substrate was explored. The interactions between PLA, THY, and PEG were observed by Fourier transform infrared (FTIR), and the intensity of color changes was measured using UV-VIS spectroscopy. It was found that the PLA pH film has a clear color response from colorless to blue at pH 11–13 with a rapid response time within a minute. The results also revealed that varying PEG content showed a significant effect on response time compared to varying the THY content. Real-time visual color changes of the PLA pH film with different THY content and PEG content on total color difference, (∆E) values over pH and time were observed. Color changes after immersion in buffer solutions with different pH values were evaluated spectrophotometrically using CIELAB color space. The results indicated that varying the PEG content in the film leads to a faster and more distinct reversible color change. This outcome can be attributed to PEG ability to augment the free volume within the PLA material and enabling PEG and the dye and become trapped between PLA chain. The addition of PEG and THY has improved the flexibility of PLA film, which enables great potential in many applications such as medical, textile, and packaging in base environments.