Journal: ACS applied materials & interfaces
Water-repellent superhydrophobic (SH) surfaces promise nearly endless applications, from increased buoyancy to drag reduction, but their practical use is limited. This comes from the fact that a SH surface will start to lose its efficiency once it is forced into water or damaged by mechanical abrasion. Here, we circumvent these two most-challenging obstacles and demonstrate a highly floating multi-faced SH metallic assembly inspired by the diving bell spiders and fire ant assemblies. We study and optimize, both theoretically and experimentally, the floating properties of the design. The assembly shows an unprecedented floating ability; it can float back to surface even after being forced submerging under water for months. More strikingly, the assembly maintains its floating ability even after severe damage and piercing in stark contrast to conventional watercrafts and aquatic devices. The potential use of the SH floating metallic assembly ranges from floating devices and electronic equipment protection, to highly floatable ships and vessels.
Passive oxide layers on metal substrates impose remarkable interfacial resistance for electron and phonon transport. Here, a scalable surface activation process is presented for the breakdown of the passive oxide layer and the formation of nanowire/nanopyramid structured surfaces on metal substrates, which enables high-efficiency catalysis of high-crystallinity carbon nanotubes (CNTs) and the direct integration of the CNT-metal hierarchical architectures with flexible free-form configurations. The CNT-metal hierarchical architecture facilitates a dielectric free-energy-carrier transport pathway and blocks the reformation of passive oxide layer, and thus demonstrates a 5-fold decrease in interfacial electrical resistance with 66% increase in specific surface area compared with those without surface activation. Moreover, the CNT-metal hierarchical architectures demonstrate omnidirectional blackbody photoabsorption with the reflectance of 1 × 10-5 over the range from ultraviolet to terahertz region, which is 1 order of magnitude lower than that of any previously reported broadband absorber material. The synergistically incorporated CNT-metal hierarchical architectures offer record-high broadband optical absorption with excellent electrical and structural properties as well as industrial-scale producibility.
We present a multifunctional tactile sensor inspired by human hairy skin structure, in which the sensitive hair sensor and the robust skin sensor are integrated into a single device via a pair of Co-based ferromagnetic microwire arrays in a very simple manner. The sensor possesses a self-tunable effective compliance with respect to the magnitude of the stimulus, allowing a wide range of loading force to be measured. The sensor also exhibits some amazing functions, such as air-flow detection, material property characterization, and excellent damage resistance. The novel sensing mechanism and structure provide a new strategy for designing multifunctional tactile sensors and show great potential applications on intelligent robot and sensing in harsh environments.
We report the new development of fire extinguishing agents employing the latest technology of fighting and preventing fires. The in situ technology of fighting fires and explosions involves using large-scale ultrafast-gelated foams, which possess new properties and unique characteristics, in particular, exceptional thermal stability, mechanical durability and full biocompatibility. We provide a detailed description of the physico-chemical processes of silica foam formation at the molecular level and functional comparison with current fire extinguishing and fighting agents. The new method allows to produce controllable gelation silica hybrid foams in the range from 2 to 30 seconds up to 100 Pa·s viscosity. Chemical structure and hierarchical morphology obtained by SEM and TEM images develop thermal insulation capabilities of the foams, reaching a specific heat value of more than 2.5 kJ/(kg·°С). The produced foam consists of organized silica nanoparticles as determined by XPS and X-Ray diffraction analysis with a narrow particle size distribution of about 10-20 nm. As a result of fire extinguishing tests, it is shown that the extinguishing efficiency exhibited by silica-based sol-gel foams is almost 50 times higher than that for ordinary water and 15 times better than that for state-of-the-art firefighting agent AFFF(aqueous film forming foam). The biodegradation index determined by the time of the induction period was only 3 days, while even for conventional foaming agents this index is several times higher.
Electrochromic polymers (ECPs) have been shown to be synthetically tunable, producing a full palette of vibrantly colored to highly transmissive polymers. The development of these colored-to-transmissive ECPs employed synthetic design strategies for broad color targeting; however, due to the subtleties of color perception and the intricacies of polymer structure and color relationships, fine color control is difficult. In contrast, color mixing is a well-established practice in the printing industry. We have identified three colored-to-transmissive switching electrochromic polymers, referred to as ECP-Cyan (ECP-C), ECP-Magenta (ECP-M), and ECP-Yellow (ECP-Y), which, via the co-processing of multicomponent ECP mixtures, follow the CMY color mixing model. The presented work qualitatively assesses the thin film characteristics of solution co-processed ECP mixtures. To quantitatively determine the predictability of the color properties of ECP mixtures, we estimated mass extinction coefficients (εmass) from solution spectra of the CMY ECPs and compared the estimated and experimentally observed color values of blends via a calculated color difference (ΔEab). The values of ΔEab range from 8 to 26 across all mixture compositions, with an average value of 15, representing a reasonable degree of agreement between predicted and observed color values. We demonstrate here the ability to co-process ECP mixtures into vibrantly colored, visually continuous films and the ability to estimate the color properties produced in these mixed ECP films.
The morphology and electronic structure of metal oxides, including TiO2 on the nanoscale, definitely determine their electronic or electrochemical properties, especially those relevant to application in energy devices. For this purpose, a concept for controlling the morphology and electrical conductivity in TiO2, based on tuning by electrospinning, is proposed. We found that the 1D TiO2 nanofibers surprisingly gave higher cyclic retention than 0D nanopowder, and nitrogen doping in the form of TiO2Nx also caused further improvement. This is due to higher conductivity and faster Li+ diffusion, as confirmed by electrochemical impedance spectra. Our findings provide an effective and scalable solution for energy storage efficiency.
Optical biosensing techniques have become of key importance for label-free monitoring of biomolecular interactions in the current proteomics era. Together with an increasing emphasis on high-throughput applications in functional proteomics and drug discovery, there has been demand for facile and generally applicable methods for the immobilization of a wide range of receptor proteins. Here, we developed a polymer platform for microring resonator biosensors, which allowed the immobilization of receptor proteins on the surface of waveguide directly without any additional modification. A sol-gel process based on a mixture of three precursors was employed to prepare a liquid hybrid polysiloxane, which was photopatternable for the photocuring process and UV imprint. Waveguide films were patterned on silicon substrates and characterized by atomic force microscopy for roughness, and protein adsorption. The results showed that the spin-coating polymer surface was smooth (Rms = 0.658 nm), and exhibits a moderate hydrophobicity with the water contact angle of 97 degree. Such a hydrophobic extent could provide a necessary binding strength for stable immobilization of proteins on the material surface in various sensing conditions. Biological activity of the immobilized Staphylococcal protein A and its corresponding biosensing performance were demonstrated by its specific recognition of human Immunoglobulin G. This study showed the potential of preparing dense, homogeneous, highly specific, and highly stable biosensing surfaces by immobilizing receptor proteins on polymer-based optical devices through the direct physical adsorption method. We expect that such polymer waveguide could be of special interest in developing low-cost and robust optical biosensing platform for multidimensional arrays.
Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells because of their high chemical stability, unique swelling ability, ion exchange capacity and rheological properties. Here we report the improved performance of a quasi-solid-state gel electrolyte comprising a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanism in the gel electrolyte, and nanoclay interactions with TiO2/electrolyte interface are discussed in detail. The electrochemical analysis reveals that the charge transport is solely based on physical diffusion. The calculated physical diffusion coefficient shows that the diffusion of redox ions is not much affected by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in electrolyte has the effect of buffering the protonation process at TiO2/electrolyte interface, resulting in conduction band up-shift and a boost in Voc. Higher Voc with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. 10 % improvement in the efficiency for hydrotalcite clay gel electrolyte is obtained, compared to that of the liquid electrolyte. The power conversion efficiency can be achieved as high as 10.1% under 0.25 sun and 9.6% under full sun. This study demonstrates that nitrate-hydrotalcite nanoclay in the electrolyte not only solidifies the liquid electrolyte to prevent solvent leakage, but also facilitates the improvement in cell efficiency.
We develop a simple approach to fabricate graphene loaded TiO2 thin films on glass substrates by spin-coating technique. Our graphene-loaded TiO2 films were highly conductive, transparent and showed enhanced photocatalytic activities. More significantly, graphene-TiO2 films displayed super-hydrophilicity within short time even under white fluorescent light bulb, as compared to a pure TiO2 film. The enhanced photocatalytic activity of graphene-TiO2 films is attributed to its efficient charge separation, owing to electrons injection from the conduction band of TiO2 to graphene. The electroconductivity of the graphene loaded TiO2 thin film also contributes to the self-cleaning function by its anti-fouling effect against particulate contaminants. The present study reveals the ability of graphene as a low cost co-catalyst instead of expensive noble metals (Pt, Pd), and further shows its capability for the application of self-cleaning coatings with transparency. The promising characteristics of (inexpensive, transparent, conductive, super-hydrophilic, and high photocatalytic active) graphene loaded TiO2 films may have the potential use in various indoor applications.
We report the fabrication of a highly flexible indium tin oxide (ITO) electrode that is completely transparent to light in the visible spectrum. The electrode was fabricated via the formation of a novel ITO nanoarray structure, consisting of discrete globular ITO nanoparticles superimposed on an agglomerated ITO layer, on a heat-sensitive polymer substrate. The ITO nanoarray spontaneously assembled on the surface of the polymer substrate by a simple sputter coating at room temperature, without nanolithographic or solution-based assembly processes being required. The ITO nanoarray exhibited a resistivity of approximately 2.3 × 10(-3) Ω cm and a specular transmission of about 99% at 550 nm, surpassing all previously reported values of these parameters in the case of transparent porous ITO electrodes synthesized via solution-based processes at elevated temperatures. This novel nanoarray structure and its fabrication methodology can be used for coating large-area transparent electrodes on heat-sensitive polymer substrates, a goal unrealizable through currently available solution-based fabrication methods.