Mechanically Robust Research Articles

Mechanically Robust Superamphiphobic Aluminum Surface with Nanopore-Embedded Microtexture

A simple fabrication technique was developed for preparing a mechanically robust superamphiphobic surface on an aluminum (Al) plate. Dual geometric architectures with micro- and nanoscale structures were formed on the surface of the Al plate by a combination of simple chemical etching and anodization. This proposed methodology involves (1) fabrication of irregular microscale plateaus on the surface of the Al plate, (2) formation of nanopores, and (3) fluorination. Wettability measurements indicated that the fabricated Al surface became super-repellent toward a broad range of liquids with surface tension in the range 27.5-72 mN/m. By varying the anodization time, we measured and compared the effects of morphological change on the wettability. The adhesion property and mechanical durability of the fabricated superamphiphobic Al surface were evaluated by the Scotch tape and hardness tests, respectively. The results showed that the fabricated Al surface retained mechanical robustness because the down-directed surface made by nanopores on the microtextured surface was durable enough even after high force was applied. Almost no damage of the film was observed, and the surface still exhibited superamphiphobicity after the tests. The fabricated superamphiphobic surface also remained stable after long-term storage. The simple and time-saving fabrication technique can be extended to any large-area three-dimensional surface, making it potentially suitable for large-scale industrial fabrications of mechanically robust superamphiphobic surfaces.

Advances in Metal Supported Cells in the METSOFC EU Consortium

AbstractThe EU‐sponsored project “METSOFC”, completed at the end of 2011, resulted in a number of advancements toward implementing a mechanically robust metal support as the structural element in SOFC. Technical University of Denmark (DTU) Energy Conversion's research into planar metal supported cells (MSCs) has produced an advanced cell design with high performance and mechanical robustness. At low operation temperatures (650 °C), these cells have shown low Area‐specific resistances (ASRs): 0.35 Ω cm2 in cell tests (16 cm2 active area) and under 0.3 Ω cm2 in button cells (0.5 cm2 active area). Further success was attained with even larger cell areas of 12 × 12 cm2 squares, which facilitated integration into small stacks at Topsoe Fuel Cell having powers approaching 1/2 kW. Development of MSC stacks showed that the MSCs could achieve similar or better performance, compared to most standard industrial anode supported ceramic cells. The best stacked MSCs had power densities approaching 275 mW cm–2 (at 680 °C and 0.8 V). Furthermore, extended testing at AVL determined extra stack performance and reliability characteristics, including behavior toward sulfur and simulated diesel reformate, and tolerance to thermal cycles and load cycles. These and other key outcomes of the METSOFC consortium are covered, along with associated work supported by the Danish National Advanced Technology Foundation.

Chitin Nanofiber Micropatterned Flexible Substrates for Tissue Engineering†

Engineered tissues require enhanced organization of cells and extracellular matrix (ECM) for proper function. To promote cell organization, substrates with controlled micro- and nanopatterns have been developed as supports for cell growth, and to induce cellular elongation and orientation via contact guidance. Micropatterned ultra-thin biodegradable substrates are desirable for implantation in the host tissue. These substrates, however, need to be mechanically robust to provide substantial support for the generation of new tissues, to be easily retrievable, and to maintain proper handling characteristics. Here, we introduce ultra-thin (<10 μm), self-assembled chitin nanofiber substrates micropatterned with replica molding for engineering cell sheets. These substrates are biodegradable, mechanically strong, yet flexible, and easily manipulated into the desired shape. As a proof-of-concept, fibroblast cell proliferation, elongation, and alignment were studied on the developed substrates with different pattern dimensions. On the optimized substrates, the majority of the cells aligned (<10°) along the major axis of micropatterned features. With the ease of fabrication and mechanical robustness, the substrates presented herein can be utilized as versatile system for the engineering and delivery of ordered tissue in applications such as myocardial repair.

Defect-activated self-assembly of multilayered graphene paper: a mechanically robust architecture with high strength

In this work molecular dynamics simulations are carried out to investigate the defect-mediated self-assembly of graphene paper from several layers of graphene sheets with vacancy defects. Tensile and shear deformations are applied to the obtained architectures to investigate both the in-plane and the out-of-plane mechanical properties. The effect of incipient defect coverage is analyzed and super-ductility is observed in the high defect density situation. While the stiffness and strength decrease with the increasing of incipient defect coverage under in-plane deformations, they increase under out-of-plane deformations, which can be attributed to the enhanced defect-induced interlayer cross-linking. Effects of crack-like flaws are also investigated to demonstrate the robustness of this structure. Our results demonstrate that defects, which are sometimes unavoidable and undesirable, can be engineered in a favorable way to provide a new approach for graphene-based self-assembly of vertically aligned architectures with mechanical robustness and high strength.

Mechanically robust Si nanorod arrays on Cu/Ti bilayer film coated Si substrate for high performance lithium-ion battery anodes

The deformation behavior and mechanical properties of a tilted Si nanorod array structure on Cu/Ti bilayer film coated Si substrate were studied for the first time by coupled atomic force microscopy and nanoindentation techniques. The individual Si nanorods fabricated by an oblique angle deposition technique are composed of many fine Si nanofibers with the diameter ranging from 10 to 50 nm. They are not brittle, but ductile. The ductile metallic Cu/Ti bilayer film roots contribute remarkably to the mechanical robustness of the Si nanorods. The toughening mechanism of such Si-based nanoanodes has been elucidated by experimental mechanics studies.

Mechanically robust polysiloxane-ACA capsules for prolonged ethanol production

Background Fermentation using encapsulated yeast leads to more robust ethanol production from lignocellulose hydrolyzates. Encapsulated yeast is much more tolerant to inhibitors present in hydrolyzates, and fermentation is faster due to increased total cell density. For industrial applications, capsules must be made robust enough to endure long periods and numerous cultivations without breaking. Results Liquid core alginatechitosanalginate (ACA) capsules containing Saccharomyces cerevisiae were produced by the liquid-droplet-forming method and treated with hydrolyzed 3-aminopropyltrietoxysilane (hAPTES) forming very glossy capsules. Capsules produced with 3.0% hAPTES showed the best mechanical robustness but no ethanol could be produced in dilute-acid spruce hydrolyzate using these capsules. Untreated ACA capsules gave the highest ethanol production but demonstrated poor mechanical robustness. 25% of the ACA capsules ruptured within 6 h in the shear test. Capsules treated with 1.5% hAPTES were significantly stronger, since only 02% of these capsules broke. Moreover, the ethanol production in the fifth consecutive cultivation in lignocellulose hydrolyzate was nearly as high as for untreated ACA capsules. Conclusion The mechanical robustness of ACA capsules can be easily improved by treating the capsules with hAPTES. ACA capsules treated with 1.5% hAPTES showed excellent mechanical robustness and a similar ethanol production profile to untreated ACA capsules.

On-Orbit Verification of a 4 × 4 Switch Matrix for Space Applications based on the Low Temperature Co-fired Ceramics Technology

We have developed a compact, high-performance, mechanically robust reconfigurable microwave switch matrix as well as peripheral components such as diode driver, voltage controlled oscillator, and power detector modules for satellite applications using the low temperature co-fired ceramics technology (LTCC) and hybrid integration of integrated circuits. In order to verify the technology for space applications, we combined these components to build a system that enables automated verification of the switch matrix in space, accounting for power consumption, mass, overall geometrical dimensions, and mechanical robustness. The system passed a full space qualification. During a one year On-Orbit-Verification (OOV) mission aboard the German test satellite TET-1 (technology evaluation carrier) launched on July 22, 2012, the correct operation and reliability of the entire switch matrix system and thereby the used technology will be demonstrated.

Thermo-compressive transfer printing for facile alignment and robust device integration of nanowires

Controlled alignment and mechanically robust bonding between nanowires (NWs) and electrodes are essential requirements for reliable operation of functional NW-based electronic devices. In this work, we developed a novel process for the alignment and bonding between NWs and metal electrodes by using thermo-compressive transfer printing. In this process, bottom-up synthesized NWs were aligned in parallel by shear loading onto the intermediate substrate and then finally transferred onto the target substrate with low melting temperature metal electrodes. In particular, multi-layer (e.g. Cr/Au/In/Au and Cr/Cu/In/Au) metal electrodes are softened at low temperatures (below 100 °C) and facilitate submergence of aligned NWs into the surface of electrodes at a moderate pressure (∼5 bar). By using this thermo-compressive transfer printing process, robust electrical and mechanical contact between NWs and metal electrodes can be realized. This method is believed to be very useful for the large-area fabrication of NW-based electrical devices with improved mechanical robustness, electrical contact resistance, and reliability.

Knitted graphene-nanoribbon sheet: a mechanically robust structure

In this paper, a new nanostructure is proposed, namely, the knitted graphene-nanoribbon sheet (KGS), which consists of zigzag and/or armchair graphene nanoribbons. The knitting technology is introduced to graphene nanotechnology to produce large area graphene sheets. Compared with pristine graphene, the chirality of a knitted graphene-nanoribbon sheet is much more flexible and can be designed on demand. The mechanical properties of KGSs are investigated by molecular dynamics simulations, including the effect of vacancies. With hydrogen atoms saturating the ribbon edges, the structure (KGS + H) is found to be of significant mechanical robustness, whose fracture does not rely on the critical bonds. The fracture strain of KGS + H remains nearly unchanged as long as there remains a single defect-free graphene nanoribbon in the tensile direction. This graphene nano knitting technique is experimentally feasible, inspired by a recent demonstration by Fournier et al. [Phys. Rev. B, 2011, 84, 035435] of lifting a single molecular wire using a combined frequency-modulated atomic force and tunnelling microscope.

Fabrication of mechanically robust superhydrophobic surfaces based on silica micro-nanoparticles and polydimethylsiloxane

Surfaces with superhydrophobicity are important in a number of biological and industrial processes. Hierarchical film based on polydimethylsiloxane (PDMS) and SiO 2 with a water contact angle of 155° and sliding angle of 6° was prepared by a facile drop-coating method. Surface modification of SiO 2 spheres was found to improve particle dispersion and increase their compatibility with PDMS, which eventually affected the stability of the hierarchical structure. Different curing temperatures were studied for enhancing the hydrophobicity of the hierarchical structure. We examined the mechanical robustness of the superhydrophobic surface by using a shear test, and found that the hierarchical PDMS-based SiO 2 films retained superhydrophobicity after 48 KPa mechanical shears.

Mechanically robust superhydrophobicity on hierarchically structured Si surfaces

Improvement of the robustness of superhydrophobic surfaces is critical in order to achievecommercial applications of these surfaces in such diverse areas as self-cleaning, waterrepellency and corrosion resistance. In this study, the mechanical robustness ofsuperhydrophobic surfaces was evaluated on hierarchically structured silicon surfaces. Theeffect of two-scale hierarchical structures on robustness was investigated using an abrasiontest and the results compared to those of superhydrophobic surfaces fabricated frompolymeric materials and from silicon that contains only nanostructures. Unlike thepolymeric and nanostructure-only surfaces, the hierarchical structures retainedsuperhydrophobic behavior after mechanical abrasion.

Robust Superhydrophobic Mats based on Electrospun Crystalline Nanofibers Combined with a Silane Precursor

We demonstrate the fabrication of solvent-resistant, mechanically robust, superhydrophobic nanofibrous mats by electrospinning of poly(vinylidene fluoride) (PVDF) in the presence of inorganic silane materials. The solvent resistance and mechanical strength of nanofibrous mats were dramatically increased through the crystallization of as-spun PVDF fibers or incorporation of a tetraethyl orthosilicate (TEOS) sol into the nanofibrous matrix. The electrospun nanofibrous mats yielded a water contact angle of 156 degrees that did not vary with TEOS content. The solvent resistance and mechanical robustness of the electrospun mats were significantly enhanced through extensive cross-linking of TEOS, even after short PVDF annealing times. The interpenetrating polymer network, which embeds polymer chains in a TEOS network, allows the fabrication of robust functional nanofibers by combining semicrystalline polymers with electrospinning techniques.

Highly Selective Polymer Electrolyte Membranes from Reactive Block Polymers

A series of reactive poly(norbornenylethylstyrene-s-styrene)-poly(n-propyl-p-styrenesulfonate) (PNS−PSSP) block polymers were prepared by atom transfer radical polymerization. Solutions containing PNS−PSSP, the cyclic olefins dicyclopentadiene and/or cyclooctene, and the second-generation Grubbs metathesis catalyst were prepared, cast as thin films, and allowed to cure at room temperature by a ring-opening metathesis polymerization mechanism. Small-angle X-ray scattering (SAXS) data on cured films were consistent with the formation of nanostructured materials containing PSSP domains confined in a cross-linked matrix of the metathesis-reactive PNS block and the poly(cyclic olefins). The PSSP phase in these films was converted into the sulfonic acid form by hydrolysis of the propyl sulfonate ester. The resulting cross-linked polymer electrolyte membranes (PEMs) were characterized by SAXS and transmission electron microscopy. A bicontinuous morphology with continuous domains of the sulfonic acid phase supported by a continuous and mechanically robust phase was evident in these films. The molecular weight of the PNS−PSSP block polymer controlled the domain sizes, and the mechanical properties of the membranes could be tuned through the choice of cyclic olefins used. The PEMs exhibited pronounced mechanical and thermal robustness. Furthermore, proton conductivities in all the PEMs were similar to those observed in Nafion (the most frequently used PEM in fuel cells) at high humidity. Select PEMs showed significantly lower methanol crossover than Nafion while maintaining high-saturated proton conductivities, which could result in higher direct methanol fuel cell power densities. This reactive block polymer strategy for the preparation of PEMs is attractive due to the ready formation of bicontinuous structures, the facile control of domain size, and the ability to independently control mechanical and swelling properties of the matrix material.

Fabrication and Characterization of High Aspect Ratio Conducting Polymer Fibers

AbstractElectroactive conducting polymers are currently studied for use in smart textiles that incorporate sensing, actuation, control, and data transmission. The development of intelligent garments that integrate these various functionalities over wide areas (i.e. the human body) requires the production of long, highly conductive, and mechanically robust fibers. This study focuses on the electrical, mechanical and electrochemical characterization of high aspect ratio polypyrrole fibers produced using a novel, custom-built fiber slicing instrument. In order to ensure high conductivity and mechanical robustness, the fibers are sliced from tetra-ethylammonium hexafluorophosphate-doped polypyrrole thin films electrodeposited onto a glassy carbon crucible. The computer-controlled, four-axis slicing instrument precisely cuts the film into thin, long fibers by running a sharp blade over the crucible in a continuous helical pattern. This versatile fabrication process has been used to produce free-standing fibers with square cross-sections of 2 μm × 3 μm, 20 μm × 20 μm, and 100 μm × 20 μm with lengths of 15 mm, 460 mm, and 1,200 mm, respectively. An electrochemical dynamic mechanical analyzer built in-house for nano- and microfiber testing was used to perform stress-strain and conductivity measurements in air. The fibers were found to, on average, have an elastic modulus of 1.7 GPa, yield strength of 37 MPa, ultimate tensile strength of 80 MPa, elongation at break of 49%, and an electrical conductivity of 12,700 S/m. SEM micrographs show that the fibers are free of defects and have cleanly cut edges. Preliminary measurements of the fibers’ strain-resistance relationship have resulted in gage factors suitable for strain sensing applications. Initial tests of the actuation performance of fibers in neat 1-butyl-3-methylimidazolium hexaflourophosphate have shown promising results. These monofilament fibers may be spun into yarns or braided into 2- and 3-dimensional structures for use as actuators, sensors, antennae, and electrical interconnects in smart fabrics.

Responding double-porous lipid membrane: Lyotropic phases in a polymer scaffold

The large osmotic gradient over the outermost layer of human skin implies major structural changes along the gradient, which in turn affects transport. In particular, the possibility of phase changes introduces a non-linear element to the transport behaviour. We present a novel model membrane system to be used for studying these transport mechanisms, where we use a hydrophobic porous polymer membrane as a scaffold for lipid lyotropic phases. The polymer membrane provides mechanical robustness, but also prevents defects of the lipid lyotropic phases, and it can induce an orientation of anisotropic phases. We study the location, structure and phase behaviour of the confined phases. It is shown that this model membrane system allow for accurate measurements of transport through lipid membranes in the presence of different osmotic gradients. A theoretical description is evaluated and shows that this phenomenon can be understood in terms of the proposed mechanism of phase changes. The novel double-porous lipid membrane constitutes a mechanically robust system for studies in aligned systems, which is generally very difficult to achieve. This could have large implications for studies of transport processes in, e.g. skin and other biomembrane model systems.

Mechanically robust amine derivatized polystyrene for pH sensing based on polymer swelling

Beads that change size as a function of pH have been prepared by suspension polymerization of vinylbenzyl chloride crosslinked with divinyl benzene followed by reaction with pure diethanolamine. Toluene is added to induced porosity, and Kraton G1652, a styrene-ethylene,butylene-styrene triblock copolymer, is included to increase mechanical robustness. The optimum formulation includes 48% toluene by volume and 2% (w/w) Kraton G1652. As the pH decreases, protonation of the amine puts a charge on the amine, causing the polymer to swell due to electrostatic repulsion between charged sites on the polymer. After the polymer is conditioned by exposure to acid, the ratio of the diameter in acid to the diameter in base is as high as 1.6 at an ionic strength of 0.10 M. The diameter ratio decreases with increasing ionic strength as predicted by theory. The diameter changes continuously from pH 6.0 to 8.0. This means that immobilization shifts the p K a of the amine. The polymer beads undergo many swelling and shrinking cycles without degrading mechanically but are softer than desired for use in a pH sensor based on polymer swelling.