† Electronic Supplementary Information (ESI) available: FTIR spectra, Raman spectrum, 1 H NMR spectra, UV-visible spectra, mass spectrum, HPLC spectra, DSC heating curves, tensile stress-strain curves, effect of exposure time of xenon lamp light on Young's modulus, and tabulated mechanical properties and healing efficiencies. See For realizing sunlight stimulated self-healing, a crosslinked polyurethane carrying disulfide in the main chain is synthesized. Its macromolecular composition and architecture are optimized so that the included disulfide bonds can take part in exchange reaction simply under illumination of the low concentration UV component of sunlight. Accordingly, the damaged polymer is allowed to be repeatedly healed in the sun in terms of strength restoration as a result of phototriggered reversible exchange of disulfide bonds. Meanwhile, the elaborately introduced hydrogen bonding helps to quickly close crack, favoring intimate contacts of cracked surface and subsequent interaction of dangling chains across the interface, and eventually raising effectiveness of photo-reaction of the disulfide bonds in solid phase. In addition, networks rearrangement due to disulfide exchange enables multiple recycling and reshaping of the polymer under sunshine. The present proof-of-concept work would be hopefully developed into a cost-effective and environmentally friendly technology of design, fabrication and application of smart photo-sensitive polymer with higher mechanical strength.
A flexible, biocompatible, nitrile butadiene rubber (NBR)-based strain sensor with high stretchability, good sensitivity, and excellent repeatability is presented for the first time. Carbon black (CB) particles were embedded into an NBR matrix via a dissolving-coating technique, and the obtained NBR/CB composite was coated with polydopamine (PDA) to preserve the CB layer. The mechanical properties of the NBR films were found to be significantly improved with the addition of CB and PDA, and the produced composite films were noncytotoxic and highly biocompatible. Strain-sensing tests showed that the uncoated CB/NBR films possess a high sensing range (strain of ∼550%) and good sensitivity (gauge factor of 52.2), whereas the PDA/NBR/CB films show a somewhat reduced sensing range (strain of ∼180%) but significantly improved sensitivity (gauge factor of 346). The hysteresis curves obtained from cyclic strain-sensing tests demonstrate the prominent robustness of the sensor material. Three novel equations were developed to accurately describe the uniaxial and cyclic strain-sensing behavior observed for the investigated strain sensors. Gloves and knee/elbow covers were produced from the films, revealing that the signals generated by different finger, elbow, and knee movements are easily distinguishable, thus confirming that the PDA/NBR/CB composite films can be used in a wide range of wearable strain sensor applications.
We report a combined experimental and numerical study of the effect of boundary layer (BL) fluctuations on the scaling properties of the mean temperature profile $\unicode[STIX]{x1D703}(z)$ and temperature variance profile $\unicode[STIX]{x1D702}(z)$ in turbulent Rayleigh–Bénard convection in a thin disk cell and an upright cylinder of aspect ratio unity. Two scaling regions are found with increasing distance $z$ away from the bottom conducting plate. In the BL region, the measured $\unicode[STIX]{x1D703}(z)$ and $\unicode[STIX]{x1D702}(z)$ are found to have the scaling forms $\unicode[STIX]{x1D703}(z/\unicode[STIX]{x1D6FF})$ and $\unicode[STIX]{x1D702}(z/\unicode[STIX]{x1D6FF})$, respectively, with varying thermal BL thickness $\unicode[STIX]{x1D6FF}$. The functional forms of the measured $\unicode[STIX]{x1D703}(z/\unicode[STIX]{x1D6FF})$ and $\unicode[STIX]{x1D702}(z/\unicode[STIX]{x1D6FF})$ in the two convection cells agree well with the recently derived BL equations by Shishkina et al. (Phys. Rev. Lett., vol. 114, 2015, 114302) and by Wang et al. (Phys. Rev. Fluids, vol. 1, 2016, 082301). In the mixing zone outside the BL region, the measured $\unicode[STIX]{x1D703}(z)$ remains approximately constant, whereas the measured $\unicode[STIX]{x1D702}(z)$ is found to scale with the cell height $H$ in the two convection cells and follows a power law, $\unicode[STIX]{x1D702}(z)\sim (z/H)^{\unicode[STIX]{x1D716}}$, with the obtained values of $\unicode[STIX]{x1D716}$ being close to $-1$. Based on the experimental and numerical findings, we derive a new equation for $\unicode[STIX]{x1D702}(z)$ in the mixing zone, which has a power-law solution in good agreement with the experimental and numerical results. Our work demonstrates that the effect of BL fluctuations can be adequately described by the velocity–temperature correlation functions and the new BL equations capture the essential physics.
Achieving fast ionic conductivity in the electrolyte at low operating temperatures while maintaining the stable and high electrochemical performance of solid oxide fuel cells (SOFCs) is challenging. Herein, we propose a new type of electrolyte based on perovskite Sr0.5Pr0.5Fe0.4Ti0.6O3−δ for low-temperature SOFCs. The ionic conducting behavior of the electrolyte is modulated using Mg doping, and three different Sr0.5Pr0.5Fe0.4–x Mg x Ti0.6O3−δ (x = 0, 0.1, and 0.2) samples are prepared. The synthesized Sr0.5Pr0.5Fe0.2Mg0.2Ti0.6O3−δ (SPFMg0.2T) proved to be an optimal electrolyte material, exhibiting a high ionic conductivity of 0.133 S cm–1 along with an attractive fuel cell performance of 0.83 W cm–2 at 520 °C. We proved that a proper amount of Mg doping (20%) contributes to the creation of an adequate number of oxygen vacancies, which facilitates the fast transport of the oxide ions. Considering its rapid oxide ion transport, the prepared SPFMg0.2T presented heterostructure characteristics in the form of an insulating core and superionic conduction via surface layers. In addition, the effect of Mg doping is intensively investigated to tune the band structure for the transport of charged species. Meanwhile, the concept of energy band alignment is employed to interpret the working principle of the proposed electrolyte. Moreover, the density functional theory is utilized to determine the perovskite structures of SrTiO3−δ and Sr0.5Pr0.5Fe0.4–x Mg x Ti0.6O3−δ (x = 0, 0.1, and 0.2) and their electronic states. Further, the SPFMg0.2T with 20% Mg doping exhibited low dissociation energy, which ensures the fast and high ionic conduction in the electrolyte. Inclusively, Sr0.5Pr0.5Fe0.4Ti0.6O3−δ is a promising electrolyte for SOFCs, and its performance can be efficiently boosted via Mg doping to modulate the energy band structure.
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