In this study, we fabricated a stretchable Silver nanowires (Ag NWs)/PDMS composite strain sensor with arbitrary micro-pattern electrodes using dispensing nozzle printing. In order to ensure a ...mechanically stable design, we proposed two types of electrodes: patterns of overlapped rings and diamonds. We also demonstrated that the electrical resistance could be modified according to the printing speed because the number of conductive fillers was proportional to the liquid ejection time. We also conducted static simulation for the two geometries to study the effect of the patterns when the strain sensor is stretched. We achieved highly stretchable strain sensor (up to 60% strain) with a suitable electrode design. Based on experimental results, it is expected that directly drawn electronic skin (E-skin) via the printing method can be fabricated with multifunctional sensing abilities in the near future.
The high-volume synthesis of two-dimensional (2D) materials in the form of platelets is desirable for various applications. While water is considered an ideal dispersion medium, due to its abundance ...and low cost, the hydrophobicity of platelet surfaces has prohibited its widespread use. Here we exfoliate 2D materials directly in pure water without using any chemicals or surfactants. In order to exfoliate and disperse the materials in water, we elevate the temperature of the sonication bath, and introduce energy via the dissipation of sonic waves. Storage stability greater than one month is achieved through the maintenance of high temperatures, and through atomic and molecular level simulations, we further discover that good solubility in water is maintained due to the presence of platelet surface charges as a result of edge functionalization or intrinsic polarity. Finally, we demonstrate inkjet printing on hard and flexible substrates as a potential application of water-dispersed 2D materials.
Microwave heating is very popular in food industries as well as in home and office to warm up foodstuffs quickly. However, this technique provides non-uniform heating within the system. The potential ...existence of standing wave due to the transmission and reflection from interfaces is responsible for this non-uniform heating. Therefore, it is important to study the coupling between electromagnetic wave propagation and energy transfer in the system to predict the temperature distribution within the foodstuff. In this paper, a closed-form analytic solution is presented to predict the temperature distribution within a cylindrical shaped foodstuff under microwave heating by solving an unsteady energy equation. A simplified Maxwell’s equation is solved for electric field distribution within the body. The heat generation by microwave is calculated from the electric field distribution within the body using Poynting theorem. The effects of cylinder radius, heat transfer coefficient and incident frequency are studied for different length of the cylindrical foodstuff. It is found that the temperature within the body is very sensitive to cylinder length and time. The results indicate that uniform and effective heating depend on the proper integration of geometric parameters and dielectric properties of the object as well as the frequency of the incident electromagnetic wave. This rigorous analytic investigation will provide significant insight to understand and overcome the challenge of non-uniformity in temperature distribution in microwave heating.
The hydrogel of biomolecule-assisted metal/organic complex has the superior ability to form a uniform, continuous, and densely integrated structure, which is necessary for fine thin film fabrication. ...As a representative of nature-originated polymers with abundant reactive side chains, we select the gelatin molecule as an element for weaving the metal cations. Here, we demonstrate the interaction between the metal cation and gelatin molecules, and associate it with coating quality. We investigate the rheological property of gelatin solutions interacting with metal cation from the view of cross-linking and denaturing of gelatin molecules. Also, we quantitatively compare the corresponding interactions by monitoring the absorbance spectrum of the cation. The coated porous structure is systematically investigated from the infiltration of gelatin-mediated Gd
Ce
O
(GDC) precursor into Sm
Sr
CoO
(SSC) porous scaffold. By applying the actively interacting gelatin-GDC system, we achieve a thin film of GDC on SSC with excellent uniformity. Compare to the discrete coating from the typical infiltration process, the optimized thin film coated structure shows enhanced performance and stability.
Abstract
For effective ocean energy harvesting, it is necessary to understand the coupled motion of the piezoelectric nanogenerator (PENG) and ocean currents. Herein, we experimentally investigate ...power performance of the PENG in the perspective of the fluid–structure interaction considering ocean conditions with the Reynolds number (
Re
) values ranging from 1 to 141,489. A piezoelectric polyvinylidene fluoride micromesh was constructed via electrohydrodynamic (EHD) jet printing technique to produce the β-phase dominantly that is desirable for powering performance. Water channel was set to generate water flow to vibrate the flexible PENG. By plotting the
Re
values as a function of nondimensional bending rigidity (
K
B
) and the structure-to-fluid mass ratio (
M*
), we could find neutral curves dividing the stable and flapping regimes. Analyzing the flow velocities between the vortex and surroundings via a particle image velocimetry, the larger displacement of the PENG in the chaotic flapping regime than that in the flapping regime was attributed to the sharp pressure gradient. By correlating
M
*,
Re
,
K
B
, and the PENG performance, we conclude that there is critical
K
B
that generate chaotic flapping motion for effective powering. We believe this study contributes to the establishment of a design methodology for the flexible PENG harvesting of ocean currents.
Microsupercapacitors (MSCs) have garnered considerable attention as a promising power source for microelectronics and miniaturized portable/wearable devices. However, their practical application has ...been hindered by the manufacturing complexity and dimensional limits. Here, we develop a new class of ultrahigh areal number density solid-state MSCs (UHD SS-MSCs) on a chip via electrohydrodynamic (EHD) jet printing. This is, to the best of our knowledge, the first study to exploit EHD jet printing in the MSCs. The activated carbon-based electrode inks are EHD jet-printed, creating interdigitated electrodes with fine feature sizes. Subsequently, a drying-free, ultraviolet-cured solid-state gel electrolyte is introduced to ensure electrochemical isolation between the SS-MSCs, enabling dense SS-MSC integration with on-demand (in-series/in-parallel) cell connection on a chip. The resulting on-chip UHD SS-MSCs exhibit exceptional areal number density 36 unit cells integrated on a chip (area = 8.0 mm × 8.2 mm), 54.9 cells cm
and areal operating voltage (65.9 V cm
).
Organic–inorganic hybrid layer-by-layer (LBL) composite structures can not only increase the strength and ductility of materials but also well disperse nanomaterials for better-conducting pathways. ...Here, we discovered the self-assembly process of an organic and silver (Ag) LBL hybrid structure having excellent sustainability during the long-term bending cycle. During the assembly process, the organic and Ag hybrid structure can be self-assembled into a layered structure. Unlike other conventional LBL fabrication processes, we applied the hydrogel scaffold of a biological polymer, which can spontaneously phase separate into an LBL structure in a water/alcohol solvent system. This new hydrogel-based Ag LBL patterns can successfully be printed on a flexible polyimide film without nozzle-clogging problem. Although these Ag LBL patterns cracked during the bending cycle, carbonized organic compounds between the Ag layers help to self-heal within few minutes at a low temperature (<80 °C). On the basis of our new hydrogel-based Ag ink, we could fabricate a fully printed reliable microscale flexible heater. We expect that our self-layering phenomenon can expand to the broad research field of flexible electronics in the near future.
In this study, we investigated the electrical and mechanical characteristics of an Ag-grid flexible transparent electrode (FTE) as a flexible and even foldable transparent electrode for flexible ...electronic devices. The Ag-grid FTE was fabricated on a polyethylene terephthalate substrate using the electrohydrodynamic (EHD) jet printing process. We achieved a fine pattern of a line width of 4.6μm. The Ag-grid FTE exhibited the sheet resistances of ~4Ω/sq. and optical transmittance of around 80% with a pitch of 150μm. We also used the carbon treated black metal-nanoparticles to lower the haze up to 1%. The effects of the sintering temperature on the microstructure and sheet resistance were investigated. From the sintering temperature of 150°C, a stable necking between nano-particles began to form, and the sheet resistance substantially decreased. The mechanical flexibility and durability of the Ag-grid FTEs were investigated via bending, stretching, dynamic/static fatigue tests, and adhesion tests. The outward bending test results showed that the Ag-grid FTE can be bent up to 3mm without failure of the electrode. The stretching test indicated that the Ag-grid FTEs can be stretched to a tensile strain of 9%; however, the Ag-grid was slightly vulnerable at the extreme bending radius in the bending cyclic fatigue tests due to severe strain accumulation. The Ag-grid FTEs exhibited a very stable static bending fatigue property during the 1000h test as well as an excellent adhesion property. These results indicate that the Ag-grid FTE is a promising electrode scheme for bendable or foldable electronic devices.
•We fabricated a flexible transparent electrode (FTE) electrohydrodynamic printing.•We achieved a fine pattern of 4.6μm with 1% haze.•Ag-grid FTE has a superior electrical and optical properties with flexibility.•Ag-grid FTE is a promising electrode for bendable or foldable electronic devices.
In the field of soft electronics, high-resolution and transparent structures based on various flexible materials constructed via various printing techniques are gaining attention. With the support of ...electrical stress-induced conductive inks, the electrohydrodynamic (EHD) jet printing technique enables us to build high-resolution structures compared with conventional inkjet printing techniques. Here, EHD jet printing was used to fabricate a high-resolution, transparent, and flexible strain sensor using a polydimethylsiloxane (PDMS)/xylene elastomer, where repetitive and controllable high-resolution printed mesh structures were obtained. The parametric effects of voltage, flow rate, nozzle distance from the substrate, and speed were experimentally investigated to achieve a high-resolution (5 µm) printed mesh structure. Plasma treatment was performed to enhance the adhesion between the AgNWs and the elastomer structure. The plasma-treated functional structure exhibited stable and long strain-sensing cycles during stretching and bending. This simple printing technique resulted in high-resolution, transparent, flexible, and stable strain sensing. The gauge factor of the strain sensor was significantly increased, owing to the high resolution and sensitivity of the printed mesh structures, demonstrating that EHD technology can be applied to high-resolution microchannels, 3D printing, and electronic devices.
Among the diverse approaches for improving the electrode performance of solid oxide fuel cells operating at intermediate temperatures, the use of nanofiber-based electrodes has provided large ...improvement owing to their large specific surface area, continuous conduction pathway, and highly porous structure. However, the low thermal stability at increased temperature often limits the process compatibility and sustainability during operation. In this study, we fabricated nanofiber-based electrodes with a high porosity and hollow shape using one-step electrospinning with a hydrogel polymer, which exhibited largely improved performance and excellent thermal stability. A porous-nanofiber-based cell exhibits a polarization resistance of 0.021 Ωcm
2
and maximum power density of 1.71 W/cm
2
at 650 °C, which is an improvement of 34.3% and 14.7% compared to that of a solid-nanofiber-based cell, respectively. Comprehensive analyses of the microstructures and chemistry indicate that the performance increase is mainly attributable to the enhanced surface oxygen exchange reactions owing to the extended reaction sites with lower energy barriers by the high porosity and enriched oxygen vacancies in the nanofibers.
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