Hydrophobic-hygroscopic, pH indicator-based fabric coatings with humidity tolerance for rapid colorimetric NH3 sensing

Although pH indicator-based, chromic fabrics are advantageous for monitoring the pH of aqueous solutions, they usually require a long time to respond to acidic or alkaline gases. Endowing hygroscopicity to such fabrics could significantly shorten the response time to gas, but moisture-absorption-driven color changes tend to decrease their reliability. Herein, we report the fabrication of hydrophobic-hygroscopic, pH indicator-based chromic fabric coatings with humidity tolerance for rapid colorimetric NH 3 sensing. The fabric coatings were fabricated by grafting a polymerizable pH indicator (cresol red), hygroscopic monomer, and hydrophobic monomer onto cotton fabrics. The resulting fabrics exhibited opposing hygroscopicity and hydrophobicity. Hydrophobicity, reflected by high water contact angles up to 139.4°, prevented color change induced by various aqueous solutions, and hygroscopicity, with moisture absorption capacity up to 11.3 %, did not have an influence on color change, with color preserved in all relative humidity ranges. After moisture absorption, the fabrics possessed a remarkable color change from yellow to purple upon exposure to alkaline gases (such as NH 3 ), and the color change could be realized within 5 s. The color change was reversible, and a reusability over 10 cycles was confirmed without obvious deterioration in color change. The simple fabrication, hydrophobicity-hygroscopicity, and rapid response to NH 3 via visual color change make the fabrics an excellent candidate for rapid NH 3 sensing and food spoilage monitoring via changes in color.