Superomniphobic Papers for On‐Paper pH Sensors

Paper-based superomniphobic surfaces are of great interest because paper is flexible, inexpensive, lightweight, breathable, and recyclable. Prior reports on paper-based superomniphobic surfaces have failed to demonstrate high mobility with low surface tension liquids. In order to overcome this issue, in this work, superomniphobic papers are developed through growth of nanofilaments on inherent microfibers of papers without noticeably altering their microscale features (i.e., diameter and distance of the microfibers). These superomniphobic papers display very low roll-off angle, indicative of ultra-high droplet mobility, even with low surface tension liquids. Here, a facile method is also developed to control the motion and adhesion of the droplets on the superomniphobic paper. Utilizing such liquid mobility in a controlled manner on these superomniphobic papers, a simple on-paper pH sensor is fabricated. It is anticipated that this on-paper, simple, and rapid detection methodology can also be extended to the colorimetric sensing of protein and chemical assays. Further, these superomniphobic papers have potential applications in water-oil separation and enhanced weight-bearing capacity.