Tunable Dimensions Research Articles

Porous textured ceramics with controlled grain size and orientation

Texture in ceramics can enhance their functional and structural properties. Current methods for texturation in dense ceramics employ plate-like particles or microplatelets as starting powders and processes that drive their orientation into specific directions. Using ultra-low magnetic fields combined with slip casting, it is possible to purposely orient magnetically responsive particles in any direction. Here, we explore the application of magnetic slip casting to bimodal slurries containing alumina nanoparticles and alumina microplatelets of various dimensions to create texture in ceramics with different grain sizes. After sintering, the obtained ceramics show anisotropic grains with controllable orientations, grain length of 3–7 μm, mild open porosity between 30–40 %, and interesting cracking behavior. Textured porous ceramics with tunable grain dimensions and orientations are promising for filtering, biomedical or composite applications.

Shaping colloidal bananas to reveal biaxial, splay-bend nematic, and smectic phases.

Understanding the impact of curvature on the self-assembly of elongated microscopic building blocks, such as molecules and proteins, is key to engineering functional materials with predesigned structure. We develop model "banana-shaped" colloidal particles with tunable dimensions and curvature, whose structure and dynamics are accessible at the particle level. By heating initially straight rods made of SU-8 photoresist, we induce a controllable shape deformation that causes the rods to buckle into banana-shaped particles. We elucidate the phase behavior of differently curved colloidal bananas using confocal microscopy. Although highly curved bananas only form isotropic phases, less curved bananas exhibit very rich phase behavior, including biaxial nematic phases, polar and antipolar smectic-like phases, and even the long-predicted, elusive splay-bend nematic phase.

Libraries of Uniform Magnetic Multicore Nanoparticles with Tunable Dimensions for Biomedical and Photonic Applications.

Multicore iron oxide nanoparticles, also known as colloidal nanocrystal clusters, are magnetic materials with diverse applications in biomedicine and photonics. Here, we examine how both of their characteristic dimensional features, the primary particle and sub-micron colloid diameters, influence their magnetic properties and performance in two different applications. The characterization of these basic size-dependent properties is enabled by a synthetic strategy that provides independent control over both the primary nanocrystal and cluster dimensions. Over a wide range of conditions, electron microscopy and X-ray diffraction reveal that the oriented attachment of smaller nanocrystals results in their crystallographic alignment throughout the entire superstructure. We apply a sulfonated polymer with high charge density to prevent cluster aggregation and conjugate molecular dyes to particle surfaces so as to visualize their collection using handheld magnets. These libraries of colloidal clusters, indexed both by primary nanocrystal dimension (dp) and overall cluster diameter (Dc), form magnetic photonic crystals with relatively weak size-dependent properties. In contrast, their performance as MRI T2 contrast agents is highly sensitive to cluster diameter, not primary particle size, and is optimized for materials of 50 nm diameter (r2 = 364 mM-1 s-1). These results exemplify the relevance of dimensional control in developing applications for these versatile materials.

Development of acoustic liner in aero engine: a review

Noise reduction for aircraft engine has attracted great concern due to the strict noise control regulation nowadays. Conventional perforated sheet-over-honeycomb acoustic liners have been widely used to attenuate turbofan engine noise. To dampen the broadband noise and resist the harsh service conditions with high temperature and pressure in modern turbofan engine, new acoustic liner concepts are proposed and evaluated in the latest decade. In this review, available studies regarding the recent development of liners are gathered. The paper starts with the introduction of acoustic absorption mechanism of local-reacting and extended-reacting liners. The progress of novel passive liners (e.g., mesh-cap liner, variable-depth liner, metal foam liner, hybrid liner, etc.) is summarized. Furthermore, adaptive liners with tunable geometry dimension or bias flow are illustrated in details. Metamaterial is also mentioned as a hot candidate in the next generation of acoustic liners. Finally, this review identifies benefits and some technical challenges with the goal of unveiling the potential of novel acoustic liner technologies in aero engine.

Modeling fractal aggregates of polydisperse particles with tunable dimension

A generalized non-kinetic off-lattice algorithm to construct stochastic fractal clusters of polydisperse particles with tunable cluster parameters including dimension, is presented. The model based on a hierarchical procedure extends the previous studies in this area to the general case of the cluster-cluster aggregation and, in contrast to the previous kinetic models, makes it possible to generate clusters with a continuous change in the structure, in particular, covering the full range of natural mass fractal dimensions between one and three. An example of the morphological study of numerically generated clusters based on the correlation analysis in both direct and reciprocal spaces is given. In the latter case, it is demonstrated that the use of the developed fast algorithm gives an accurate and self-consistent description of the small-angle scattering data.

Electrofluidynamic Patterning of Tailorable Nanostructured Substrates for Surface-Enhanced Raman Scattering.

The unique attributes of surface enhanced Raman spectroscopy (SERS) make it well suited to address the challenges associated with portable diagnostics. However, despite the remarkable progress in this field, where the instrumentation has made great strides forward providing a route to the miniaturization of sensing devices, to date producing three-dimensional low-cost SERS substrates which simultaneously fulfill the multitude of criteria of high sensitivity, reproducibility, tunability, multiplexity, and integratability for rapid sensing has not yet been accomplished. Successful implementation of SERS requires readily fine-tuned nanostructures, which create a high enhancement. Here, an advanced electrofluidynamic patterning (EFDP) technique enables rapid fabrication of SERS active topographic morphologies with high throughput and at a nanoresolution via the spatial and lateral modulation of the dielectric discontinuity due to the high electric field generated across the polymer nanofilm and air gap. The subsequent formation of displacement charges within the nanofilm by coupling to the electric field yield a destabilizing electrostatic pressure and amplification of EFDP instabilities enabling the controllable pattern formation. The top of each gold coated EFDP fabricated pillar generates controllable high SERS enhancement by coupling of surface plasmon modes on top of the pillar, with each nanostructure acting as an individual sensing unit. The absolute enhancement factor depends on the topology as well as the tunable dimensions of the nanostructured units, and these are optimized in the design and engineering of the dedicated EFDP apparatus for reproducible, low-cost fabrication of the three-dimensional nanoarchitectures on macrosurfaces, rendering them for easy integration in further lab-on-a-chip devices. This unique combination of nanomaterials and nanospectroscopic systems lay the platform for a variety of applications in chemical and biological sensing.

A High-Efficiency Wideband Frequency-Reconfigurable Water Antenna With a Liquid Control System: Usage for VHF and UHF Applications

A distilled water dielectric resonator antenna (DRA) with a wide frequency-tuning range and high efficiency is presented in this article. It consists of a water resonator and a ground plane with a wideband bowtie feeding slot. The water resonator, having tunable dimensions, is employed to achieve frequency-reconfigurable characteristics. Mechanical switches and a microfluid pump are integrated to control the tuning process. The water DRA, with and without the liquid control system, is designed with a simulation tool and then fabricated and measured to validate the antenna's performance. It is demonstrated that the antenna exhibits high total efficiency (> 80%) across a wide frequency-tuning range from 168 to 474 MHz (for S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , -10 dB) with a very compact volume of 278 × 278 × 131 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (0.155λ × 0.155m × 0.073m at 168 MHz). Compared with traditional reconfigurable antennas, this design provides a wider frequency-tuning range, a more compact size, and a higher degree of design freedom. It is therefore a promising candidate for very high-frequency (VHF) and ultrahigh-frequency (UHF) applications.

Self-Reducible Conjugated Microporous Polyaniline for Long-Term Selective Cr(VI) Detoxication Driven by Tunable Pore Dimension.

A simple methodology to controllably tune the pore size and Cr(VI) adsorption capacity was reported herein to synthesize a new series of conjugated microporous polyaniline (CMPA) networks. The well-ordered micropore was acquired through our very recent Bristol-Xi'an Jiaotong method, and the pore size was fine-tuned to increase with the increasing length of linkers, mimicking covalent organic frameworks and metal organic frameworks very much. A selective ultrahigh adsorption capacity of 520.8 mg/g was achieved by CMPA-1 in a very fast manner, with a systematically gradual decrease to 173.9 mg/g of CMPA-3 by enlarging the pore size of the networks, featuring tunable adsorption capacity through molecular-size-recognition mechanism. Additionally, our robust CMPA networks, which were constructed by Buchwald-Hartwig chemistry, showed the complete function of polyaniline and were capable of providing, besides large storage capacity for Cr(III), at least 10 reductant/desorption-free cycles for effective Cr(VI) reduction and detoxication through their novel self-reducible redox states. Outcomes showed that our CMPAs could be applied as new self-healing scavengers in the next generation for Cr(VI) storage and detoxication.

Programmable and Reversible 3D-/4D-Shape-Morphing Hydrogels with Precisely Defined Ion Coordination.

Precise and programmable control of reversible deformations of hydrogels has important implications for bionics. This work reports on programmable three-dimensional (3D) deformations and thermoresponsive actuation of polymer hydrogels in a well-defined manner. Precise infiltration of Fe3+ with periodic patterns is additionally used to cross-link the local polymer network through ionoprinting with a patterned electrode array. The patterned Fe3+ cross-linking generates periodic undulations in cross-link density, stiffness, and thermoresponsiveness. The internal stress induces 3D helical structures with tunable chirality and dimensions. The differential thermoresponsiveness imbues a fourth dimension to the shape deformations. Moreover, sequential ionoprinting generates well-defined in-plane periodic distributions of differential modulus and responsiveness, leading to 3D/4D umbrella-like origami upon temperature triggers.

Gold Nanoearbuds: Seed-Mediated Synthesis and the Emergence of Three Plasmonic Peaks.

We demonstrate the first successful synthesis of reasonably monodisperse and single-crystalline gold nanoearbuds (Au NEBs) using a binary surfactant mixture of cetyltrimethylammonium chloride (CTAC) and benzyldimethylhexadecylammonium chloride (BDAC) in seed-mediated growth method. We have focused on the key chemical parameters behind the formation and growth of Au NEBs to result in tunable dimensions (length, 37-77 nm; width, 4-6 nm; aspect ratio, 7-19), as a consequence of which the longitudinal surface plasmon resonance (LSPR) peak could be tuned beyond 1200 nm. The achievement of LSPR beyond 1200 nm while maintaining the dimension well below 100 nm is a challenging accomplishment in the realm of one-dimensional (1D) Au nanostructures. This earbud-like morphology additionally exhibits three plasmonic peaks, rather uncommon for 1D nanostructures, which were analyzed theoretically based on the finite element method. The new resonance peak of the Au NEB was assigned as an additional longitudinal mode intensified by the bulbous ends as well as the high aspect ratio, thereby providing conclusive evidence that it is indeed a new morphology.

General synthesis of two-dimensional van der Waals heterostructure arrays

Two-dimensional van der Waals heterostructures (vdWHs) have attracted considerable interest1-4. However, most vdWHs reportedso far are created by an arduous micromechanical exfoliation and manual restacking process5, which-although versatile for proof-of-concept demonstrations6-16 and fundamental studies17-30-is clearly not scalable for practical technologies. Here we report a general synthetic strategy for two-dimensional vdWH arrays between metallic transition-metal dichalcogenides (m-TMDs) and semiconducting TMDs (s-TMDs). By selectively patterning nucleation sites on monolayer or bilayer s-TMDs, we precisely control the nucleation and growth of diverse m-TMDs with designable periodic arrangements and tunable lateral dimensions at the predesignated spatial locations, producing a series of vdWH arrays, including VSe2/WSe2, NiTe2/WSe2, CoTe2/WSe2, NbTe2/WSe2, VS2/WSe2, VSe2/MoS2 and VSe2/WS2. Systematic scanning transmission electron microscopy studies reveal nearly ideal vdW interfaces with widely tunable moiré superlattices. With the atomically clean vdW interface, we further show that the m-TMDs function as highly reliable synthetic vdW contacts for the underlying WSe2 with excellent device performance and yield, delivering a high ON-current density of up to 900microamperes per micrometre in bilayer WSe2 transistors. This general synthesis of diverse two-dimensional vdWH arrays provides a versatile material platform for exploring exotic physics and promises a scalable pathway to high-performance devices.

Fabrication of ultrasound-mediated tunable graphene oxide nanoscrolls.

In this work, a cost-effective and facile method was adopted for the fabrication of graphene oxide nanoscrolls (GONS) by low frequency (20kHz) ultrasonication with tunable dimensions. The graphene oxide (GO) was synthesized by modified Hummer's method using synthetic graphite as a base material. Later, GO suspension (0.05gL-1) were made using methanol as solvent and subjected to different ultrasonication conditions. It was found that GO sheets curls themselves into nanoscrolls by overcoming the energy barrier for scrolling with the help of bubble cavitation energy provided by ultrasonication. Also, the effect of ultrasonication power (100-150W) for irradiation time (0.5-3h) over the GONS dimensions were investigated. The spiral wounded GONS structures were shown using electron microscopy. Raman Spectroscopy, Thin-film X-Ray Diffraction, Energy Dispersive X-Ray, FT Infrared Spectroscopic analysis were also done to endorse GONS formation. Factors affecting GONS formation such as sonication power and solvent selection were studied as scrolling of GO sheets are strongly dependent on sonication parameters and solvent characteristics. It was found that GONS length varies inversely with irradiation time for identical power density. Also, a solvent with relatively large Hansen solubility parameter, lower dipole movement and less negative value of zeta potential support GONS formation of longer length. Raman analysis overlays the rapid oxygen-defect site cleavage mechanism. The obtained GONS unlocks further developments in various engineering applications like adsorption, drug delivery and filtration membrane.

Direct Writing Micropatterns with a Resolution up to 1 µm

AbstractSolution processes have been widely used to fabricate micropatterned surfaces for its mild operation conditions. However, current approaches suffer from limitations of either low resolution or high cost. Here, a facile approach is proposed for direct writing micropatterns with a resolution up to ≈1 µm using a unit of triple conical fibers with the side‐by‐side parallel arrangement. With this unit, the resolution of the micropatterns can be mainly controlled by the single central conical fiber, with one side of the fiber facilitating continuous and steady liquid transfer onto the substrate and the other side mechanically supporting the whole unit. Particularly, the unit enables tunable dimension of the micropatterns within a rather large scale from ≈1 µm to ≈1.3 mm by varying the writing parameters (speed, height, and angle). Moreover, the unit is applicable for direct patterning various liquids, even into microline arrays, with a high resolution. It enables direct writing conductive microline with a width of ≈1 µm in a centimeter length scale, which can be used for constructing microcircuits. It is envisioned that the result offers a new perspective for preparing high‐resolution micropatterns using solution processes.

SBA-15 Anchored Metal Containing Catalysts in the Oxidative Desulfurization Process

Recalcitrant sulfur compounds are common impurities in crude oil. During combustion they produce SOx derivatives that are able to affect the atmospheric ozone layer, increasing the formation of acid rains, and reducing the life of the engine due to corrosion. In the last twenty years, many efforts have been devoted to develop conventional hydrodesulfurization (HDS) procedures, as well as alternative methods, such as selective adsorption, bio-desulfurization, oxidative desulfurization (ODS) under extractive conditions (ECODS), and others. Among them, the oxidative procedures have been usually accomplished by the use of toxic stoichiometric oxidants, namely potassium permanganate, sodium bromate and carboxylic and sulfonic peracids. As an alternative, increasing interest is devoted to selective and economical procedures based upon catalytic methods. Heterogeneous catalysis is of relevance in industrial ODS processes, since it reduces the leaching of active species and favors the recovery and reuse of the catalyst for successive transformations. The heterogenization of different types of high-valent metal transition-based organometallic complexes, able to promote the activation of stoichiometric benign oxidants like peroxides, can be achieved using various solid supports. Many successful cases have been frequently associated with the use of mesoporous silicas that have the advantage of easy surface modification by reaction with organosilanes, facilitating the immobilization of homogeneous catalysts. In this manuscript the application of SBA-15 as efficient support for different active metal species, able to promote the catalytic ODS of either model or real fuels is reviewed, highlighting its beneficial properties such as high surface area, narrow pore size distribution and tunable pore diameter dimensions. Related to this topic, the most relevant advances recently published, will be discussed and critically described.

Engineering a Bi-Conical Microchip as Vascular Stenosis Model.

Vascular stenosis is always associated with hemodynamic changes, especially shear stress alterations. Herein, bi-conical shaped microvessels were developed through flexibly and precisely controlled templated methods for hydrogel blood-vessel-like microchip. The blood-vessel-like microvessels demonstrated tunable dimensions, perfusable ability, and good cytocompatibility. The microchips showed blood-vessel-like lumens through fine embeddedness of human umbilical vein endothelial cells (HUVECs) on the interior surface of hydrogel microchannels, which closely reproduced the morphology and functions of human blood vessels. In the gradual narrowing region of bi-conical shape, fluid flow generated wall shear stress, which caused cell morphology variations. Wall shear rates at the gradual narrowing region were simulated by FLUENT software. The results showed that our microchannels qualified for performance as a vascular stenosis-like model in evaluating blood hydrodynamics. In general, our blood-vessel-on-a-chip could offer potential applications in the prevention, diagnosis, and therapy of arterial thrombosis.

Conversion of Mg‐Li Bimetallic Alloys to Magnesium Alkoxide and Magnesium Oxide Ceramic Nanowires

AbstractTechnologically important composites with enhanced thermal and mechanical properties rely on the reinforcement by the high specific strength ceramic nanofibers or nanowires (NWs) with high aspect ratios. However, conventional synthesis routes to produce such ceramic NWs have prohibitively high cost. Now, direct transformation of bulk Mg‐Li alloys into Mg alkoxide NWs is demonstrated without the use of catalysts, templates, expensive or toxic chemicals, or any external stimuli. This mechanism proceeds through the minimization of strain energy at the boundary of phase transformation front leading to the formation of ultra‐long NWs with tunable dimensions. Such alkoxide NWs can be easily converted in air into ceramic MgO NWs with similar dimensions. The impact of the alloy grain size and Li content, synthesis temperature, inductive and steric effects of alkoxide groups on the diameter, length, composition, ductility, and oxidation of the produced NWs is discussed.

Conversion of Mg-Li Bimetallic Alloys to Magnesium Alkoxide and Magnesium Oxide Ceramic Nanowires.

Technologically important composites with enhanced thermal and mechanical properties rely on the reinforcement by the high specific strength ceramic nanofibers or nanowires (NWs) with high aspect ratios. However, conventional synthesis routes to produce such ceramic NWs have prohibitively high cost. Now, direct transformation of bulk Mg-Li alloys into Mg alkoxide NWs is demonstrated without the use of catalysts, templates, expensive or toxic chemicals, or any external stimuli. This mechanism proceeds through the minimization of strain energy at the boundary of phase transformation front leading to the formation of ultra-long NWs with tunable dimensions. Such alkoxide NWs can be easily converted in air into ceramic MgO NWs with similar dimensions. The impact of the alloy grain size and Li content, synthesis temperature, inductive and steric effects of alkoxide groups on the diameter, length, composition, ductility, and oxidation of the produced NWs is discussed.

Cage-confinement pyrolysis route to size-controlled molybdenum-based oxygen electrode catalysts: From isolated atoms to clusters and nanoparticles

Metal-nitrogen-carbon materials with properly tailored metal particle sizes offer an ideal model system for electrocatalysis due to their readily tunable dimension, geometric and electronic effects at the catalytically active sites. Herein, a cage-confinement pyrolysis route is proposed to realize size-controllable synthesis of molybdenum-based catalysts ranging from isolated single Mo atoms to sub-nanometer clusters (<1 nm) and nanoparticles (2–5 nm). The effective control in the degree of dispersion facilitates a rational investigation into the electrocatalytic behavior of metal species from the angstrom to the nanometer scales. Notably, the Mo single atom catalysts show superior activity for bifunctional oxygen reduction and evolution reactions (ORR/OER) with a smaller potential gap of 0.65 V, which are compared favorably with the analogous sub-nanometer clusters and nanometer-level particles. X-ray fine structure analyses coupled with theoretical calculations demonstrate that the active Mo sites in the Mo1N1C2 local coordination environment have promoted the reversible oxygen electrode reactions. As a demonstration of their real application potentials, the zinc-air batteries assembled by using the highly active Mo single atom catalysts as the air cathode deliver a specific capacity of 750 mA h gZn−1 with an energy density of 673 W h kgZn−1, comparable to a mixed Pt/C-RuO2 benchmark.

Dual microelectrodes decorated with nanotip arrays: Fabrication, characterization and spectroelectrochemical sensing

Gold microelectrodes decorated with nanotips were developed for spectroelectrochemical experiments. These new dual probes were fabricated by combining fabrication processes of scanning near-field optical microscopy with photolithography. A nanotip array was produced at the surface of a coherent optical fiber bundle by a wet chemical etching step. The resulting nanostructured surface was sputter-coated with a thin gold layer. This gold film conferred plasmonic properties to the sharp nanotips and served as well as the electrode material to enable electrochemical reactions. A photolithographic process was used to delimit on the bundle surface nanotips-decorated microelectrodes with tunable dimensions (radii ranging between 20 μm and 3.5 μm) individually or in an array format. The resulting microelectrodes with a regular nanotip pattern were characterized first by cyclic voltammetry. Numerical simulation was used to assess the electrochemical properties of these platforms and the influences of the recessed geometry and of the nanotips. Approach curves were recorded in negative and positive feedback modes of scanning electrochemical microscopy (SECM) on insulating and conducting substrates. Finally, spatially resolved Raman imaging allowed us to detect a mercaptobenzoic acid monolayer adsorbed on the microelectrode surface, demonstrating a surface-enhanced Raman scattering (SERS) effect induced by the gold-coated nanotips with a typical enhancement factor of ∼7 × 104. Such an approach introduces a reproducible method to fabricate promising SERS-active platforms with microelectrode behavior for SECM experiments.

Tailored Nanopatterning by Controlled Continuous Nanoinscribing with Tunable Shape, Depth, and Dimension.

We present that the tailored nanopatterning with tunable shape, depth, and dimension for diverse application-specific designs can be realized by utilizing controlled dynamic nanoinscribing (DNI), which can generate bur-free plastic deformation on various flexible substrates via continuous mechanical inscription of a small sliced edge of a nanopatterned mold in a compact and vacuum-free system. Systematic controlling of prime DNI processing parameters including inscribing force, temperature, and substrate feed rate can determine the nanopattern depths and their specific profiles from rounded to angular shapes as a summation of the force-driven plastic deformation and heat-driven thermal deformation. More complex nanopatterns with gradient depths and/or multidimensional profiles can also be readily created by modulating the horizontal mold edge alignment and/or combining sequential DNI strokes, which otherwise demand laborious and costly procedures. Many practical user-specific applications may benefit from this study by tailor-making the desired nanopattern structures within desired areas, including precision machine and optics components, transparent electronics and photonics, flexible sensors, and reattachable and wearable devices. We demonstrate one vivid example in which the light diffusion direction of a light-emitting diode can be tuned by application of specifically designed DNI nanopatterns.