ABSTRACT
Hygroscopic polymers are good candidates for antifogging coatings, but their long-term effectiveness is limited by the equilibrium between water absorption and expansion. As an efficient and environmentally friendly solution, photothermal materials are being introduced into the field of antifogging. However, there is a need for enhancement in the spectral characteristics of most photothermal materials within the visible light region. In addition, photothermal antifogging coatings often exhibit a delay in heating response, which hinders their ability to promptly evaporate condensed water droplets in the absence of illumination or during initial illumination. Here, a bilayer structure design of photothermal nanomaterials/hygroscopic polymers is proposed to achieve long-term antifogging under sunlight activation. Ensuring the rapid absorption of condensed water droplets on the coating surface, while simultaneously achieving efficient photothermal conversion for a swift temperature increase over the entire coating, is key to this approach, which will not only suppress early fogging but also lead to an exponential decrease of the nucleation rate of droplets. During this process, a dynamic equilibrium is gradually established between the condensation and evaporation of fog droplets, leading to long-term antifogging properties. The light transmittance of the composite coatings reaches as high as ca. 75% in the visible light region, making them well suited for a diverse range of transparent substrate and device applications. A clear field of view can be maintained for at least 6 h under 1 sun illumination above 65 °C hot steam. The antifogging/defogging performance is effectively demonstrated even under challenging non-ideal natural conditions, such as low solar irradiation during dusk or when placed indoors behind windows.
ABSTRACT
Although a wide variety of single-function coatings have been successfully developed, the integration of multiple functions onto a single coating has remained an immense challenge in the field. Here, we report a simple room-temperature fabrication of robust coatings with UV-shielding, light conversion, and antifogging functionalities. The addition of glutaraldehyde (GA) molecular cross-linker and carbon dot (CD) nanocross-linker with light conversion function to poly(vinyl alcohol) (PVA) resulted in the formation of robust spatial structures of coatings. The fluorescence intensity tests demonstrated that the coatings had an excellent ability to absorb and convert ultraviolet light into blue-violet light. Both cold-warm and hot-vapor tests showed that the coatings had excellent antifogging performance. To our surprise, no creases were observed after coatings were immersed in water for 1 month, indicating that these are much stronger than those reported so far. The 8H pencil hardness and wear resistance attested to their excellent mechanical properties. The current preparation method can be operated at ambient temperature and is not restricted by the substrate type and shape. Therefore, it may also expand the possibilities for future applications of coatings for glass windows, optical microscopes, eyeglasses, agricultural greenhouses, and so on.
ABSTRACT
Herein, we demonstrate a facile and green rapid approach for the synthesis of uniform poriferous hydroxylapatite [Ca10(PO4)6(OH)2, HA] and poriferous silver nanoparticle (Ag NPs)-decorated hydroxylapatite (HA@Ag) nanocomposites with excellent antibacterial properties. All the nanocomposites were fully characterized in the solid state via various techniques such as X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), automatic specific surface area and porosity analysis (BET) and field emission scanning electron microscopy (FESEM). The results show that HA has a porous rod-like structure, which the HA@Ag nanocomposites retained, and the surface of HA was loaded with globular-like Ag NPs with an average diameter of about 5.8 nm, which exhibit a well-crystalline state. The experimental parameters such as pH, the molar ratio of HA and Tollens' reagent, and reductant have a significant effect on the size and distribution of the Ag NPs. Moreover, the antimicrobial activities of HA and HA@Ag against Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) were evaluated via broth dilution, filter paper diffusion, optical density (OD600) and electron microscopy observation. The as-prepared HA@Ag nanocomposites exhibit excellent antibacterial activities, especially for S. aureus. The minimum inhibition concentration (MIC) of HA@Ag is only 3.9 µg mL-1.
