Development of Optical Polyviologen Nanoparticle‐Immobilized Cellulose Nanocrystal‐Reinforced Gum Arabic as Self‐Healing Hydrogel Toward Multi‐Stimuli Responsive and Anticounterfeiting Applications

Photosensitive inks have displayed disadvantages, such as low efficiency and poor durability. In contrast, self‐healable hydrogels can independently repair physical damage to restore their structural properties, proving durability and stability. In this context, a new nanocomposite film with photochromic, thermochromic, and ammonia‐responsive characteristics was prepared from a combination of polyviologen and maleic‐modified cellulose nanocrystal‐supported gum Arabic hydrogel. The viologen polymer was synthesized using an aqueous condensation process involving a viologen dialdehyde and a hydroxyl‐functionalized aryl dihydrazide under acidic conditions. The polyviologen nanoparticles displayed a diameter range of 9–21 nm, whereas CNC showed sizes between 8 and 15 nm. The use of CNC as a dispersant inhibits the agglomeration of viologen nanoparticles. Mechanical and morphological analyses demonstrated superior adhesion, flexibility, and homogeneity of the imprinted films. A reversible thermochromic response was monitored in a temperature range of 25°C–80°C. Exposure to ammonia vapor induced a rapid color change from yellow (447 nm) to green (627 nm), which promptly returned to its original condition upon removal of the ammonia stimulus. The paper sensor identifies aqueous ammonia at values ranging from 0.1 to 350 ppm. The coating layer exhibited a green tint in UV light, as confirmed by CIE colorimetric measurements.