Development of a Nitrazine Yellow-glycidyl methacrylate coating onto cotton fabric through thermal-induced radical polymerization reactions: a simple approach towards wearable pH sensors applications

In this paper, the bifunctional monomer glycidyl methacrylate (GMA) was employed in a simple two-step synthetic strategy with the aim of developing a Nitrazine Yellow-based pH-meter wearable sensor. The catalyzed epoxy ring-opening of GMA allowed the formation of a covalent bond with the sulfonate groups of the halochromic dyestuff, while potassium persulfate thermally initiated the radical grafting of the functionalized NY onto cellulose. Both reactions have been confirmed by Nuclear Magnetic Resonance Spectroscopy and by Infrared Spectroscopy, respectively. Furthermore, the morphology of the treated cotton samples was studied by means of Scanning Electron Microscopy. The pH- halochromic behaviour of the functionalized NY molecule was studied both in solution and onto the fabrics, by means of UV–Vis Spectroscopy, UV–Vis reflectance measurements and CIELAB colour changes. All experimental findings confirmed that the immobilized NY dyestuff still pertains consistent and typical halochromic properties in the pH range 6.0–7.0. The novel functional fabric developed in this work paves the way to non-disposable and reversible wearable pH sensors in smart textiles.