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Stimuli responsive elastic instabilities provide opportunities for controlling the structures and properties of polymer surfaces, offering a range of potential applications. Here, a surface actuator based on a temperature and electrically responsive poly( N-isopropyl acrylamide-co-sodium acrylate) hydrogel that undergoes a two-step delamination and buckling instability triggered using micropatterned electrodes is described. The electrically actuated structures entail large out-of-plane displacements that take place on time-scales of less than 1 s, in response to modest triggering voltages (−3-6 V). Alongside these experimental observations, finite element simulations are conducted to better understand the two-step nature of the instability. In the first step, hydrogel films undergo delamination and formation of blisters, facilitated by electrochemical reduction of the thiol groups anchoring the film to the electrodes. Subsequently, at larger reducing potentials, the electrolytic current is sufficient to nucleate a gas bubble between the electrode and the gel, causing the delaminated region to adopt a straight-sided blister shape. Finally, thermally induced deswelling of the gel allows the film to be returned to its flat state and readhered to the electrode, thereby allowing for repeated actuation. [ABSTRACT FROM AUTHOR]

On surfaces well above 100 °C water does not simply boil away. When there is a sufficient heat transfer between the solid and the liquid a continuous vapour layer instantaneous forms under a droplet of water and the drop sits on a cushion of vapour, highly mobile and insulated from the solid surface. This is known as the Leidenfrost effect and the temperature at which this occurs if known as the Leidenfrost transition temperature. In this report, an investigation of discontinuous surfaces, stainless steel meshes, have been tested to determine the effect of the woven material on the Leidenfrost phenomenon. It was found that with increasing the open area of the mesh pushes up the Leidenfrost temperature from 265 °C for an open area of 0.004 mm 2 to 315 °C for open area of 0.100 mm 2 . This allows suppression of the Leidenfrost effect as it can be increase to over 300 °C from 185 °C for a stainless steel surface. [ABSTRACT FROM AUTHOR]

Similar to MXene, MAB is a group of 2D ceramic/metallic boride materials which exhibits unique properties for various applications. However, these 2D sheets tend to stack and therefore lose their active surface area and functions. Herein, an amorphous cobalt nickel boride (Co–Ni–B) nanocomposite is prepared with a combination of 2D sheets and nanoparticles in the center to avoid agglomeration. This unique structure holds the 2D nano-sheets with massive surface area which contains numerous catalytic active sites. This nanocomposite is prepared as an electrocatalyst for borohydride electrooxidation reaction (BOR). It shows outstanding catalytic activity through improving the kinetic parameters of BH 4 − oxidation, owing to abundant ultrathin 2D structure on the surface, which provide free interspace and electroactive sites for charge/mass transport. The anode catalyst led to a 209 mW/cm2 maximum power density with high open circuit potential of 1.06 V at room temperature in a miniature direct borohydride fuel cell (DBFC). It also showed a great longevity of up to 45 h at an output power density of 64 mW/cm2, which is higher than the Co–B, Ni–B and PtRu/C. The cost reduction and prospective scale-up production of the Co–Ni–B catalyst are also addressed. [Display omitted] • DBFC with Co–Ni–B nanocomposite as anode catalyst exhibited P max = 209 mW/cm2 which is over twice higher than PtRu/C. • MXene-like structure enhanced the exposure of active metallic species and the mass transfer. • The assembled DBFC has good stability of retaining 91.2% of the output voltage after 45 h. • The narrow band gap of Co–Ni–B nanocomposite urges the charge transfer kinetic. [ABSTRACT FROM AUTHOR]

The Leidenfrost effect allows droplets to be transported on a virtually frictionless layer of vapor above a superheated substrate. The substrates are normally topographically structured using subtractive techniques to produce saw-tooth, herringbone, and other patterns and bulk heated, leading to significant challenges in energy consumption and controlled operation. Here, we propose a planar lithographic approach to levitate and propel droplets using temperature profiles, which can be spatially patterned and controlled in time. We show that micro-patterned electrodes can be heated and provide control of the pressure profile and the vapor flow. Using these almost featureless planar substrates, we achieve self-directed motion of droplets, with velocities of approximately 30 mms−1, without topographically structuring the substrate or introducing physical walls. Our approach has the potential to be integrated into applications, such as digital microfluidics, where frictionless and contactless droplet transport may be advantageous. [ABSTRACT FROM AUTHOR]

Recent advancements in electronics engineering require materials with the resiliency and sustainability to extend their life time. With this regard, we presented a sustainable multi-functional nanocomposites strategy by introducing dynamic imine bonds based polyazomethine (PAM) as molecular interconnects and Fe 3 O 4 -loaded multiwalled carbon nanotubes as electromagnetic (EM) wave absorbing units. Driven by the reversible dynamic imine bonds, our materials show robust spontaneous self-healing with excellent healing efficiencies of 95% for PAM and 90% for nanocomposite, and an accelerated recovery under a moderate mechanical stimulus. By adding Fe 3 O 4 -loaded multiwalled carbon nanotubes, the hybrids show excellent EM wave absorbing properties with 50% increment on minimum reflection coefficient (−40.6 dB) than the reported value. We demonstrate a full degradability by decomposing a nanocomposite sheet of 100 mg in an acidic solution within 90 min at room temperature. The nanofillers and monomers after degradation can be re-used to synthesis nanocomposites. The testing results for recoverable nanocomposites show a good retention on mechanical property. This novel strategy may shed a light on the downstream applications in EM wave absorbing devices and smart structures with great potential to accelerate circular economy. Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract The reduction-responsive micelles from amphiphilic star copolymers with HyperMacs core and disulfide bonds were presented for triggered release of anticancer drugs. Highlights • Star copolymers contain long-chain hyperbranched PCL core and disulfide bonds. • The micelles exhibit low CMC, good stability and reduction-cleavable property. • The reduction-responsive star copolymers possess potential in tumor chemotherapy. Abstract In this contribution, the reduction-responsive star copolymers with long-chain hyperbranched poly(ε-caprolactone) (PCL) (HyperMacs) core and disulfide bonds were synthesized via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The HyperMacs core was constructed from disulfide-containing AB 2 -type PCL macromonomers, which possesses length-adjustable chain segments between branching points, large cavities, low degree of crystallinity, and reduction-responsivity. After grafted with poly(ethylene glycol), the reduction-responsive star copolymers can self-assemble into micelles in aqueous solution. The obtained micelles exhibited much lower critical micelle concentration (CMC) than their linear analogues. The reduction-responsivity from disulfide bonds makes them a promising carrier candidate for trigger release of anticancer drugs. The in vitro release results confirmed that their doxorubicin (DOX)-loaded micelles exhibited desirable reduction-triggered release performance. The cellular proliferation inhibition against HepG2 cells demonstrated that the DOX-loaded micelles showed a comparable anticancer activity with free DOX. Therefore, it can be expected that the reduction-sensitive micelles may serve as smart vehicles for intracellular delivery of anti-cancer drugs in tumour therapy. [ABSTRACT FROM AUTHOR]

Often wetting is considered from the perspective of a single surface of a rigid substrate and its topographical properties such as roughness or texture. However, many substrates, such as membranes and meshes, have two useful surfaces. Such flexible substrates also offer the potential to be formed into structures with either a double-sided surface (e.g. by joining the ends of a mesh as a tape) or a single-sided surface (e.g. by ends with a half-twist). When a substrate possesses holes, it is also possible to consider how the spaces in the substrate may be connected or disconnected. This combination of flexibility, holes and connectedness can therefore be used to introduce topological concepts, which are distinct from simple topography. Here, we present a method to create a Slippery Liquid-Infused Porous Surface (SLIPS) coating on flexible conformable doubled-sided meshes and for coating complex geometries. By considering the flexibility and connectedness of a mesh with the surface properties of SLIPS, we show it is possible to create double-sided SLIPS materials with high droplet mobility and droplet control on both faces. We also exemplify the importance of flexibility using a mesh-based SLIPS pipe capable of withstanding laminar and turbulent flows for 180 and 90 minutes, respectively. Finally, we discuss how ideas of topology introduced by the SLIPS mesh might be extended to create completely new types of SLIPS systems, such as Mobius strips and auxetic metamaterials. [ABSTRACT FROM AUTHOR]