Inkjet Printing Enabled Controllable Paper Superhydrophobization and Its Applications

Papers' intrinsic interconnected porous structures and hydrophilic properties usually results in difficulty and complexity in partial functionalization and regulation processes because the capillary effect may lead to the fast diffusion of modifiers from one side to the other. Here, we report a simple and innovative inkjet printing approach that led to precise hydrophobic functionalization controllable in both planar and steric dimensions. Fabrication of Janus superwetting papers and superwettable patterned papers with high precision was achieved by computer-controlled inkjet printing. Elaborate controls of ink quantity enabled superhydrophobic functionalization on one side of the paper substrate, with the opposite side superhydrophilic. Static water contact angles up to 154° were obtained on the inkjet-printed side of the paper, thanks to an appropriate combination of surface chemistry with dual-scale surface roughness. Furthermore, paper-based microfluidics were fabricated and the resolution of which were estimated to be ca. 600 μm. Meanwhile, a paper-based analytical device for colorimetric sensing of Ni(II) was designed and demonstrated based on superwettable patterned papers by inkjet printing. The inkjet printing approach reported here represents a key step forward in fabricating Janus materials and complicate patterns for practical applications.