Redox-switchable superhydrophobic silver composite

Plasmon-Driven Photochemical Reduction Reaction on Silver Nanostructures for Green Fabrication of Superhydrophobic Surface

Green fabrication of superhydrophobic surface by water-based processing is still challenging, because introduction of the substances with hydrophilic moieties compromises its superhydrophobicity. Herein, a plasmon-driven photochemical reduction reaction under ultraviolet light (UVA) irradiation is first discovered and is applied to deoxygenation of hydrophilic organic adsorbates on rough nano-Ag coating for the formation of stable superhydrophobic surface. A nano-Ag coating with strong localized surface plasmon resonance in the UVA region is prepared by a water-based silver mirror reaction and results in a unique chemical reduction reaction on its surface. Consequently, the low residual hydrophilic functionalities and the formed cross-linked structure of the adsorbate on Ag nanoparticles (NPs) enables the coating to exhibit stable superhydrophobicity against to both air and water. The superhydrophobic Ag NP-coated sandpaper can also be used as a surface-enhanced Raman scattering (SERS) substrate to concentrate aqueous analytes for trace detection.

Floatable superhydrophobic Ag2O photocatalyst without a modifier and its controllable wettability by particle size adjustment

In this research, a controlling mechanism of particle size on the wettability of Ag2O particles is reported, and an interesting floatable Ag2O photocatalyst with superhydrophobicity and superoleophilicity is prepared based on this mechanism. Stable superhydrophobic and superhydrophilic Ag2O without a low-surface-energy modifier can be obtained only by adjusting its particle size, and its wettability can switch mutually by changing the particle size. The wettability of Ag2O converts from superhydrophilic to hydrophobic when the average particle size is more than 1.08 μm. The operation parameters of the Ag2O crystallization process significantly influence the wettability of the Ag2O particles. The obtained superhydrophobic Ag2O floated on the water surface, and exhibited excellent photodegradation performance with various floating oils. This attractive superhydrophobic Ag2O photocatalyst is promising for practical applications, and provides a strategy for the development of functional photocatalysts and superhydrophobic materials.

In situ and controllable synthesis of Ag NPs in tannic acid-based hyperbranched waterborne polyurethanes to prepare antibacterial polyurethanes/Ag NPs composites

In this research, a simple and facile method was developed for preparation of antibacterial polyurethanes/Ag NPs composites, where tannic acid-based hyperbranched waterborne polyurethanes (THWPU) was employed as both reductant and stabilizer to in situ and controllably synthesize Ag NPs at mild room temperature. The resultant Ag NPs in THWPU was confirmed by UV spectrophotometer, SEM and EDX. The effects of reaction temperature on the properties of the formed Ag NPs were investigated, and the results showed that the formed Ag NPs under room temperature and 80 °C were both spherical, whereas increasing the reaction temperature benefits for promoting the formation of Ag NPs and narrowing the size distribution of the formed Ag NPs. Furthermore, triangular Ag NPs were in situ synthesized in THWPU via adding strong reductant (NaBH₄) during the formation of Ag NPs. Both spherical and triangular Ag NPs enhanced the mechanical property, thermal stability and antibacterial performance of THWPU. More importantly, our results demonstrated that formation of spherical Ag NPs in THWPU were beneficial for improving the mechanical property and thermal stability of THWPU, while the formation of triangular Ag NPs enabled THWPU better antibacterial performance against E. coli and S. aureus. Given these advantages, our obtained Ag NPs nanocomposites could be suitable for a broad range of commercial applications, such as medical products, children's products.

A simple and facile method was developed for preparation of antibacterial polyurethanes/Ag NPs composites by using tannic acid-based hyperbranched waterborne polyurethanes (THWPU).

Surfactant-free switchable emulsions using CO2-responsive particles

Surfactant-free emulsions are prepared using bi-wetting particles which occupy the oil-water interface to effectively reduce the oil-water interfacial area. The equilibrium position of the particle at the interface is determined by its wettability. CO2-reponsive chemical functional groups are grafted onto the surface of silica particles. Particles with only CO2-switchable functional groups are capable of stabilizing oil-in-water emulsions. Particles prepared with both CO2-responsive and hydrophobic chemical functional groups on its surface are capable of stabilizing water-in-oil emulsions. Emulsion stability is disturbed when the wettability of the stabilizing particle is altered by introducing CO2 gas to the biphasic mixture, leading to phase separation of emulsions prepared using the functionalized particles. The emulsion stability can be re-established by the removal of CO2 through air sparging. The presence of CO2 imposes positive surface charge to the responsive particles, increasing wettability and, consequently, the ability of the particles to destabilize emulsions.

Reversible superhydrophobic-superhydrophilic transition of ZnO nanorod/epoxy composite films

Tuning the surface wettability is of great interest for both scientific research and practical applications. We demonstrated reversible transition between superhydrophobicity and superhydrophilicity on a ZnO nanorod/epoxy composite film. The epoxy resin serves as an adhesion and stress relief layer. The ZnO nanorods were exposed after oxygen reactive ion etching of the epoxy matrix. A subsequent chemcial treatment with fluoroalkyl and alkyl silanes resulted in a superhydrophobic surface with a water contact angle up to 158.4° and a hysteresis as low as 1.3°. Under UV irradiation, the water contact angle decreased gradually, and the surface eventually became superhydrophilic because of UV induced decomposition of alkyl silanes and hydroxyl absorption on ZnO surfaces. A reversible transition of surface wettability was realized by alternation of UV illumination and surface treatment. Such ZnO nanocomposite surface also showed improved mechanical robustness.