Bioinspired Free-Standing One-Dimensional Photonic Crystals with Janus Wettability for Water Quality Monitoring.

Materials with specific wettability properties have aroused enormous interest and research for their broad application prospects in chemical reaction, medical diagnosis, biological analysis, etc. Here, inspired by the unique Janus wettability of lotus leaf and Bragg stacks of beetles, we present a free-standing film with Janus wettability and tunable structural color for water quality monitoring. This film is constructed by using a flexible polymer polyurethane (PU) to pack poly(N-isopropyl acrylamide-bis-acrylamide-acrylic acid) (P(NiPAAm-bis-AA))/TiO2 one-dimensional photonic crystals (1DPCs) into a free-standing state with Janus wettability and tunable structural color. The outer top surface of the film could achieve vivid structural color and a superhydrophobic ability; meanwhile, the outer lower surface could achieve a superhydrophilic ability. Owing to the outstanding pH-sensitive property of the P(NiPAAm-bis-AA), the Janus films could switch its structural color under different pH conditions. This imparts the free-standing film with stability and an antirotation property on the air-water interface. Based on this phenomenon, we have demonstrated a Janus wettability film, together with tunable structural color for water quality monitoring, which gives the bioinspired materials high potential applications in environmental protection.

Superhydrophobic Hybrid Paper Sheets with Janus-Type Wettability.

We introduce the design of Janus-type paper sheets where one side of the paper exhibits superhydrophobic properties, whereas the other side of the sheet remains hydrophilic and therefore can take up aqueous solutions by capillary wicking. Such papers are being prepared by chemically immobilizing a thin hybrid coating on paper sheets that consists of cross-linked poly(dimethylsiloxane) (PDMS) and inorganic particles of various sizes ranging from nanometers to several tens of micrometers. Both commercially available Whatman No. 1 filter paper and lab-engineered cotton linters-based paper substrates were treated with this approach. The hybrid paper sheets have high chemical durability, mechanical stability, and flexibility because of a covalent attachment of the particles to paper fibers and the inherent elasticity of PDMS chains. In spite of the superhydrophobicity of the coating, the untreated side of the paper substrates preserved its hydrophilicity, resulting in Janus-type wetting and wicking properties, respectively. The functionalized paper samples remained porous and permeable to gases, while possessing a gradual change in chemistry between the two sides exhibiting a dramatic wetting contrast. Such two-sided properties open up new applications for such hybrid paper materials, such as in wound dressings and/or bandages with a liquid directing and confinement ability.