NIR-Triggered Photothermal Responsive Coatings with Remote and Localized Tunable Underwater Oil Adhesion

One-step fabrication of all-in-one three-dimensional porous polypyrrole/polydopamine structure for efficient solar vapor generation

High-quality solar evaporators with all-in-one design are highly desirable for vapor generation, but relevant research is scarce. In this study, a three-dimensional (3D) porous polypyrrole/polydopamine (PPY/PDA) structure was fabricated via a simple heating-assisted rapid oxidative polymerization method. The obtained evaporator has multiple features, and can simultaneously provide rapid water transport channels (average pore sizes ∼ 18.37 nm), low thermal conductivity (0.071 W m-1 K-1), high solar absorbance (97.08%), and good mechanical properties. When it is employed as an evaporator, the calculated water evaporation rate is approximately 2.12 kg m-2h-1, which is comparable to other reported 3D evaporators. Additionally, the evaporator displays great potential for purification toward various nonpotable water, as well as reliable pure water yields in an outdoor application (from 8:00 am to 5:00 pm, the evaporator can produce at least 13.95 L of drinkable water for a 1 m2 sample). We believe that the proposed strategy to fabricate all-in-one evaporators has great significance for scientific research and practical applications.

Dually reactive multilayer coatings enable orthogonal manipulation of underwater superoleophobicity and oil adhesion via post-functionalization

Fish scale-inspired underwater superoleophobic coatings with low oil adhesion can be achieved through the creation of hierarchical surface topography on water-compatible materials (including polymeric hydrogels, metal oxides, and electrostatic multilayers). While promising, these method do not allow for the underwater superoleophobicity and oil adhesion to be independently tuned, limiting their potential applications. Here we report the design of a conceptually novel class of coatings, dually reactive multilayer coatings, whose underwater superoleophobicity and oil adhesion can be independently tuned through the orthogonal functionalization of two types of reactive moieties at ambient conditions. Moreover, the cooperative assembly of amphiphiles on the modified underwater superoleophobic coating gives rise to a switchable oil adhesion while retaining the extreme oil-repellency (advancing oil contact angle >165°). Interestingly, the reversible change in the oil adhesion of the underwater superoleophobic coatings depends on the interplay between the molecular structure and concentration of the amphiphiles and the pH of the aqueous solution. Building on these findings, we developed superoleophobic sensors that enable the real-time and naked eye identification of (1) the charge of synthetic ionic surfactants and (2) the concentration of bile acids. Overall, the results reported in this work provide design principles by which molecular self-assembly and oil adhesion can be coupled at underwater superoleophobic surfaces, and hint at principles by which physiologically important amphiphiles and metabolites can be rapidly sensed with the naked eye using our novel class of superoleophobic surfaces.

Magnetically Driven Tunable 3D Structured Fe3 O4 Vertical Array for High-Performance Solar Steam Generation

Structural design of the solar-absorbing layer has been considered as one of the most direct and effective approaches for improving the solar steam generation performance by maximizing the absorption of sunlight, but great challenges in manipulation simplification and structure controllability still remain. Herein, a polyester (PET) fabric covered with a vertically aligned 3D tower-like ferrosoferric oxide (Fe₃ O₄ ) array via a convenient magnetically driven spray-coating method is reported, and both the spatial density and height of the Fe₃ O₄ array are tunable upon spraying time. It shows an extremely high solar absorbance (98.6%) in the entire solar spectrum, which is superior to the corresponding 2D Fe₃ O₄ structure (91.1%). Combining the obtained 3D Fe₃ O₄ /PET with a yolk-shell hydrophobic/superhydrophilic modified melamine-formaldehyde (mMF) sponge, the carefully designed and fabricated 3D Fe₃ O₄ /PET-mMF evaporator can realize a high water evaporation rate of 1.59 kg m^-2 h^-1 under 1 kW m^-2 solar illumination, outperforming most related solar steam generation systems. With the advantages of cost-effectiveness, high evaporation rate, reliable endurance, and structural controllability, this 3D structural design provides an avenue to build up high-performance solar energy-driven water steam generation systems.

Electrically Induced Underwater Superaerophilicity/Superaerophobicity Switching on Polypyrrole-Coated Mesh Films for Selective Bubble Permeation

Recently, materials with controllable superwettability have attracted much attention. However, almost all studies focused on controlling wetting of water and oil; research on underwater gas bubble wetting control is still rare. Herein, we report a mesh film prepared by coating polypyrrole (PPy) film on Ti mesh. Briefly, the film mesh is underwater superaerophilic when PPy is doped with perfluorooctanesulfonate ions (PFOS^- ), and becomes underwater superaerophobic as the PFOS^- are removed. The transition of the wettability can be triggered by electrical stimuli, which is attributed to the cooperative effect between the rough structure and chemical components variation. The controllable wettability allows adjustable bubble permeation. It can be envisioned that the film will provide potential applications in the future, such as underwater bubble capture/release and microfluidic devices.

3D MXene Sponge: Facile Synthesis, Excellent Hydrophobicity, and High Photothermal Efficiency for Waste Oil Collection and Purification

Photothermally assisted superhydrophobic sponges play a vital role in the fields of waste oil collection, oil purification, and solar desalination. However, the widely reported superhydrophobic sponges with photothermal efficiency usually suffer from a post-/premodification process of harmful materials, high loading content of photothermal agents, and low photothermal efficiency. Herein, an MXene-based melamine sponge (MS) was facilely fabricated by hydrogen bonding interaction between the amino groups on the skeleton of the MS and the polar groups on the surface of the as-exfoliated 2D MXene Ti₃C₂T_x nanosheets. Interestingly, the as-fabricated MXene sponge exhibits excellent hydrophobicity and high photothermal efficiency under an extremely low loading of MXene Ti₃C₂T_x nanosheets (0.1 wt %). Moreover, the highly hydrophobic sponge also possesses a high oil absorption capacity as high as 176 times of its own weight and keeps stable under multiple absorption/desorption cycling tests. Surprisingly, the surface temperature of the MXene sponge can quickly reach 47 °C under illumination and has good reproducibility during multiple light on/off cycles. The excellent photothermal performance and large oil absorption capacity of the MXene sponge endow the highly hydrophobic sponge with fast solvent evaporation speed and high-purity waste oil collection (99.7 wt % dichloromethane) under illumination, which holds great promise for oil/water separation, leaked oil collection, and photo-driven waste oil collection and purification applications. It is envisioned that this work can open a new strategy for new designs of 3D multifunctional sponges for high-performance waste oil collection and purification.

Bioinspired programmable wettability arrays for droplets manipulation

The manipulation of liquid droplets demonstrates great importance in various areas from laboratory research to our daily life. Here, inspired by the unique microstructure of plant stomata, we present a surface with programmable wettability arrays for droplets manipulation. The substrate film of this surface is constructed by using a coaxial capillary microfluidics to emulsify and pack graphene oxide (GO) hybrid N-isopropylacrylamide (NIPAM) hydrogel solution into silica nanoparticles-dispersed ethoxylated trimethylolpropane triacrylate (ETPTA) phase. Because of the distribution of the silica nanoparticles on the ETPTA interface, the outer surface of the film could achieve favorable hydrophobic property under selective fluorosilane decoration. Owing to the outstanding photothermal energy transformation property of the GO, the encapsulated hydrophilic hydrogel arrays could shrink back into the holes to expose their hydrophobic surface with near-infrared (NIR) irradiation; this imparts the composite film with remotely switchable surface droplet adhesion status. Based on this phenomenon, we have demonstrated controllable droplet sliding on programmable wettability pathways, together with effective droplet transfer for printing with mask integration, which remains difficult to realize by existing techniques.

Light and latex: advances in the photochemistry of polymer colloids

Unparalleled temporal and spatial control of colloidal chemical processes introduces immense potential for the manufacturing, modification, and manipulation of latex particles.