Hydrophilic/Hydrophobic SiO2 Nanoparticles Enabled Janus‐Type Paper through Commercial Glaco Spraying and Air‐Plasma Treatment

Abstract Functional paper‐based microdevices have been receiving wide attention in the research areas of microfluidic chips, soft actuators, etc. This work introduces the design and fabrication of a Janus‐type paper in which one side of the paper remains hydrophilic and the other side is hydrophobic. Such Janus‐type paper is prepared by directly spraying hydrophobic Glaco solutions and following air plasma treatment. The former treatment can cover the paper fibers with numerous hydrophobic SiO 2 nanoparticles. Through optimizing the fabrication parameters of the air plasma, it can penetrate the filter paper in a controllable depth, resulting in effectively regulating the hydrophobic particles into hydrophilic ones. Thereafter, the antirotation and interfacial stability of the Janus paper are investigated. Finally, a liquid storage and contamination‐free analysis devices are demonstrated on the Janus‐type paper platform. Noting that the commercially nonfluoride coating (Glaco) and mature plasma instrument together make the fabrication method simple, rapid, users/environmental‐friendly, and mass‐produced. The method provides a new route to fabricate Janus‐type paper for potential multifunctional applications in microfluidic chips and smart actuators, and may open up new avenue to prepare Janus films in a simple/rapid way.