Elastic Halochromic Fiber as a Reversible pH Sensor

Abstract

Wearable textile colorimetric sensors are extremely effective for expressing danger or warning, as they are non‐invasive and exhibit easily recognizable color changes. However, unlike conventional sensors, these devices are actually worn by individuals and should, therefore, not only detect hazardous chemicals in real time but also maintain the reversibility, durability, and stability of color change upon exposure to sweat, repetitive movement, and environments involving continuous exposure to chemical substances. Herein, a halochromic fiber maintaining excellent pH sensing properties upon continuous exposure to chemical and physical stimuli is fabricated. The fiber surface is rendered hydrophobic by phosphonic acid treatment, and a composite pH indicator dye capable of simultaneously detecting acids and bases is embedded into the fiber pores. The halochromic fiber could accurately detect pH while maintaining a clear color transition even after repeated changes in the acidic–basic environment, returning to the neutral state within several seconds after termination of exposure to the test solution. Thus, the presented technique allows one to significantly improve the reversibility, durability, and stability of color change—a problem faced by conventional wearable sensors—and, thus, greatly contributes to the development of halochromic textile sensors applicable to real‐life work environments.

A Three-Dimensional-Printed Recyclable, Flexible, and Wearable Device for Visualized UV, Temperature, and Sweat pH Sensing

“…The one-to-one relationship between color and sweat pH proves the feasibility of visualized sweat pH sensing via methyl red. In order to assess the reversibility of sweat pH sensing, artificial sweat containing methyl red was repeatedly adjusted the pH 49 to either 4.0 or 7.0. As can be seen from Figure 3 e, artificial sweat solutions containing methyl red exhibit red and yellow periodically as sweat pH switches between 4.0 and 7.0, implying a certain reversibility of sweat pH sensing via methyl red.…”

Functional Textiles with Smart Properties: Their Fabrications and Sustainable Applications

“…To directly observe the responding behavior, Hong et al developed a halochromic fiber via the phosphonic acid treatment of PU-SnO 2 fiber and following embodiment of a composite pH indicator dye, maintaining excellent pH sensing properties upon continuous exposure to chemical and physical stimuli. [436] The halochromic fiber could accurately and reversibly detect acids and bases in both liquid and vapor phases, exhibiting at least five types of color changes, which is expected to promote the commercialization of halochromic textile sensors. Inspired by the colorimetric gas sensor based on visually discernible changes in the color of the sensing material, Kim et al chemically functionalized a composite nanofiber yarn with an ionic liquid as an effective H 2 S adsorbent and lead acetate as a colorimetric dye to prepare a colorimetric sensor via a meterscale synthesis (Figure 12i).…”

Recent advances in the material design for intelligent wearable devices

“…Hong et al used halogenated color-changing fibers to fabricate a wearable pH sensor, which could show excellent sensing performance in environments with continuous chemical and physical stimuli. 206 By embedding a composite pH indicator dye that could detect both acids and bases in the fiber pores and treating the fiber surface with phosphonic acid to hydrophobized it, the pH indicator dye was prevented from leaking onto the outer surface of the fiber when is in contact with acidic and alkaline solutions. As shown in Fig.…”