Non-Fluorine Oil Repellency: How Low the Intrinsic Wetting Threshold Can Be for Roughness-Induced Contact Angle Amplification?

Surface chemistries for realizing oil repellency are mostly based on perfluoro compounds (PFCs) owing to their low surface energy. However, PFCs are not sustainable because of their persistent and bioaccumulative properties, and their usage, even short-chain ones, has begun to be phased out. To date, studies on non-fluorine oil repellency have been extremely rare, and the obtained oil repellency has been limited. Here, we report the non-fluorine oil repellency of a coating prepared on a tightly woven plain-weave fabric through hydrolysis and polycondensation of difunctional chlorosilane. The coated fabric exhibited a contact angle of 119.0° for castor oil and 81.4° for hexadecane, as well as a contact angle of 51.9° for decane with a surface tension as low as γLV = 23.5 mN m-1. According to the standard ISO 14419:2010, oil repellency was rated Grade 6. The solid surface tension of the coating was calculated to be γSV = 22.1 mN m-1. Through the test of the difference in contact angles between rough and smooth surfaces, the intrinsic wetting threshold (θIWT) for such a surface chemistry was determined to be ranging from 8.9 to 14.5°. A study on the effects of surface morphologies suggests that the realization of an oil-repellency rating of 6 and a θIWT as low as 8.9-14.5° strongly depends on the roughness topographies. We hope that this study will be useful for the design─and our understanding─of non-fluorine oil repellency for applications including stain-resistant textiles and grease-resistant food packaging.

Multifunctional MXene/Aramid Nanofiber Composite Films for Efficient Electromagnetic Interference Shielding and Repeatable Early Fire Detection.

Rapid development of highly integrated electronic and telecommunication devices has led to urgent demands for electromagnetic interference (EMI) shielding materials that incorporate flame retardancy, and more desirably the early fire detection ability, due to the potential fire hazards caused by heat propagation and thermal failure of the devices during operation. Here, multifunctional flexible films having the main dual functions of high EMI shielding performance and repeatable fire detection ability are fabricated by vacuum filtration of the mixture of MXene and aramid nanofiber (ANF) suspensions. ANFs serve to reinforce MXene films via the formation of hydrogen bonding between the carbonyl groups of ANFs and the hydroxyl groups of MXene. When the ANF content is 20 wt %, the tensile strength of the film is increased from 24.6 MPa for a pure MXene film to 79.5 MPa, and such a composite film (9 µm thickness) exhibits a high EMI shielding effectiveness (SE) value of ∼40 dB and a specific SE (SSE) value of 4361.1 dB/mm. Upon fire exposure, the composite films can trigger the fire detection system within 10 s owing to the thermoelectric property of MXene. The self-extinguishing feature of ANFs ensures the structural integrity of the films during burning, thus allowing for continuous alarm signals. Moreover, the films also exhibit excellent Joule heating and photothermal conversion performances with rapid response and sufficient heating reliability.

A Durable, Flexible, Large-Area, Flame-Retardant, Early Fire Warning Sensor with Built-In Patterned Electrodes.

Fire has been giving rise to enormous loss of life and property worldwide annually. Early fire warning represents an active and effective means to avoid potential fire hazards before huge losses occur. Despite encouraging advances in early fire warning systems, to date there remains an urgent lack of the design of a durable, flexible, and universal early fire warning sensor for large-area practical applications. Herein, facile fabrication of a durable, flexible, large-scale early fire-warning sensor is demonstrated through constructing a hierarchical flame retardant nanocoating, composed of graphene oxide, poly(dimethylaminoethyl methacrylate), and hexagonal boron nitride, on cotton fabric in combination with the parallelly patterned conductive ink as built-in electrodes. As-designed large-scale sensor (>33 cm and extendable) exhibits a short alarming time of <3 s in response to external abnormal high temperature, heat, or fire. In addition to high washability, flexibility, resistance to abrasion and wear, this hierarchical nanocoating can self-extinguish, thus enabling the sensor to continue warning during fire. This work offers an inventive concept to develop a universal and large-scale very early fire-monitoring platform, which opens up new opportunities for their practical applications in effectively reducing fire-related casualties and economic losses.

Crafting Mussel-Inspired Metal Nanoparticle-Decorated Ultrathin Graphitic Carbon Nitride for the Degradation of Chemical Pollutants and Production of Chemical Resources.

The development of efficient photocatalysts for the degradation of organic pollutants and production of hydrogen peroxide (H2 O2 ) is an attractive two-in-one strategy to address environmental remediation concerns and chemical resource demands. Graphitic carbon nitride (g-C3 N4 ) possesses unique electronic and optical properties. However, bulk g-C3 N4 suffers from inefficient sunlight absorption and low carrier mobility. Once exfoliated, ultrathin nanosheets of g-C3 N4 attain much intriguing photocatalytic activity. Herein, a mussel-inspired strategy is developed to yield silver-decorated ultrathin g-C3 N4 nanosheets (Ag@U-g-C3 N4 -NS). The optimum Ag@U-g-C3 N4 -NS photocatalyst exhibits enhanced electrochemical properties and excellent performance for the degradation of organic pollutants. Due to the photoformed valence band holes and selective two-electron reduction of O2 by the conduction band electrons, it also renders an efficient, economic, and green route to light-driven H2 O2 production with an initial rate of 0.75 × 10-6 m min-1 . The improved photocatalytic performance is primarily attributed to the large specific surface area of the U-g-C3 N4 -NS layer, the surface plasmon resonance effect induced by Ag nanoparticles, and the cooperative electronic capture properties between Ag and U-g-C3 N4 -NS. Consequently, this unique photocatalyst possesses the extended absorption region, which effectively suppresses the recombination of electron-hole pairs and facilitates the transfer of electrons to participate in photocatalytic reactions.

Bioinspired Soot-Deposited Janus Fabrics for Sustainable Solar Steam Generation with Salt-Rejection.

Inspired by lotus leaves, self-floating Janus cotton fabric is successfully fabricated for solar steam generation with salt-rejecting property. The layer-selective soot-deposited fabrics not only act as a solar absorber but also provide the required superhydrophobicity for floating on the water. With a polyester protector, the prepared Janus evaporator exhibits a sustainable evaporation rate of 1.375 kW m-2 h-1 and an efficiency of 86.3% under 1 sun (1 kW m-2) and also performs well under low intensity and inclined radiation. Furthermore, no special apparatus and/or tedious processes are needed for preparing this device. With a cost of less than $1 per m2, this flexible Janus absorber is a promising tool for portable solar vapor generator.