Fabrication, Thermal Conductivity, and Mechanical Properties of Hexagonal-Boron-Nitride-Pattern-Embedded Aluminum Oxide Composites.

As electronics become more portable and compact, the demand for high-performance thermally conductive composites is increasing. Given that the thermal conductivity correlates with the content of thermally conductive fillers, it is important to fabricate composites with high filler loading. However, the increased viscosity of the composites upon the addition of these fillers impedes the fabrication of filler-reinforced composites through conventional methods. In this study, hexagonal-boron-nitride (h-BN)-pattern-embedded aluminum oxide (Al2O3) composites (Al/h-BN/Al composites) were fabricated by coating a solution of h-BN onto a silicone-based Al2O3 composite through a metal mask with square open areas. Because this method does not require the dispersion of h-BN into the Al2O3 composite, composites with high filler loading could be fabricated without the expected problems arising from increased viscosity. Based on the coatability and thixotropic rheological behaviors, a composite with 85 wt.% Al2O3 was chosen to fabricate Al/h-BN/Al composites. The content of the Al2O3 and the h-BN of the Al/h-BN/Al-1 composite was 74.1 wt.% and 12.8 wt.%, respectively. In addition to the increased filler content, the h-BN of the composite was aligned in a parallel direction by hot pressing. The in-plane (kx) and through-plane (kz) thermal conductivity of the composite was measured as 4.99 ± 0.15 Wm-1 K-1 and 1.68 ± 0.2 Wm-1 K-1, respectively. These results indicated that the method used in this study is practical not only for increasing the filler loading but also for achieving a high kx through the parallel alignment of h-BN fillers.

Correction: Bok et al. Super-Toughened Fumed-Silica-Reinforced Thiol-Epoxy Composites Containing Epoxide-Terminated Polydimethylsiloxanes. Int. J. Mol. Sci. 2021, 22, 8097.

The authors wish to make the following corrections to the original publication [...].

Would You Trust Driverless Service? Formation of Pedestrian's Trust and Attitude Using Non-Verbal Social Cues.

Despite the widespread application of Autonomous Vehicles (AV) to various services, there has been relatively little research carried out on pedestrian-AV interaction and trust within the context of service provided by AV. This study explores the communication design strategy promoting a pedestrian's trust and positive attitude to driverless services within the context of pedestrian-AV interaction using non-verbal social cues. An empirical study was conducted with an experimental VR environment to measure participants' intimacy, trust, and brand attitude toward AV. Further understanding of their social interaction experiences was explored through semi-structured interviews. As a result of the study, the interaction effect of social cues was found, and it was revealed that brand attitude was formed by the direct effects of intimacy and trust as well as the indirect effects of intimacy through trust's mediation. Furthermore, 'Conceptual Definition of Space' was identified to generate differences in the interplay among intimacy, trust, and brand attitude according to social cues. Quantitative and qualitative results were synthesized to discuss implications considering the service context. Practical implications were also addressed suggesting specific design strategies for utilizing the sociality of AV.

Super-Toughened Fumed-Silica-Reinforced Thiol-Epoxy Composites Containing Epoxide-Terminated Polydimethylsiloxanes.

In response to the demand for high-performance materials, epoxy thermosetting and its composites are widely used in various industries. However, their poor toughness, resulting from the high crosslinking density of the epoxy network, must be improved to expand their application to the manufacturing of flexible products. In this study, ductile epoxy thermosetting was produced using thiol compounds with functionalities of 2 and 3 as curing agents. The mechanical properties of the epoxy were further enhanced by incorporating fumed silica into it. To increase the filler dispersion, epoxide-terminated polydimethylsiloxane was synthesized and used as a composite component. Thanks to the polysiloxane-silica interaction, the nanosilica was uniformly dispersed in the epoxy composites, and their mechanical properties improved with increasing fumed silica content up to 5 phr (parts per hundred parts of epoxy resin). The toughness and impact strength of the composite containing 5 phr nanosilica were 5.17 (±0.13) MJ/m3 and 69.8 (±1.3) KJ/m2, respectively.

Fabrication of Flexible Electrode with Sub-Tenth Micron Thickness Using Heat-Induced Peelable Pressure-Sensitive Adhesive Containing Amide Groups.

In response to the increasing demand for flexible devices, there is increasing effort to manufacture flexible electrodes. However, the difficulty of handling a thin film is an obstacle to the production of flexible electrodes. In this study, a heat-induced peelable pressure-sensitive adhesive (h-PSA) was fabricated and used to manufacture a flexible electrode with sub-tenth micron thickness. Unlike the control PSA, the incorporation of amide groups made the h-PSA fail through adhesive failure at temperatures ranging from 20 to 80 °C. Compared to the peeling adhesion (1719 gf/in) of h-PSA measured at 20 °C, the value (171 gf/in) measured at 80 °C was decreased by one order of magnitude. Next, the 8 µm thick polyethylene terephthalate (PET) film was attached on a thick substrate (50 µm) via h-PSA, and Mo/Al/Mol patterns were fabricated on the PET film through sputtering, photolithography, and wet-etching processes. The thick substrate alleviated the difficulty of handling the thin PET film during the electrode fabrication process. Thanks to the low peel force and clean separation of the h-PSA at 80 °C, the flexible electrode of metal patterns on the PET (8 µm) film was isolated from the substrate with little change (<1%) in electrical conductivity. Finally, the mechanical durability of the flexible electrode was evaluated by a U-shape folding test, and no cracking or delamination was observed after 10,000 test cycles.

Thermally Conductive Film Fabricated Using Perforated Graphite Sheet and UV-Curable Pressure-Sensitive Adhesive.

Thermally conductive films play a crucial role in expanding the lifetime of electronics by dissipating concentrated heat to heatsinks. In this work, a thermally conductive film (g-TC film) was manufactured using a perforated graphite sheet (p-GS) and a UV-curable pressure-sensitive adhesive (PSA) by lamination. A novel UV-curable PSA was prepared by incorporating a UV-curable abietic acid ester into a PSA composition. The UV-curable PSA became a tack-free film upon UV irradiation; thus, a flexible g-TC film with a 52-µm thickness was obtained. The defects in the g-TC film caused by air bubbles were removed by treating the p-GS with oxygen plasma. As the UV-cured PSA made a joint through the holes in the p-GS, cleavage of the graphite was not observed after 10,000 U-folding test cycles with a folding radius of 1 mm. The calculated in-plane thermal conductivity of the fabricated g-TC film was 179 W∙m-1K-1, which was stable after the U-folding tests.

Ultra-thin and smooth transparent electrode for flexible and leakage-free organic light-emitting diodes.

A smooth, ultra-flexible, and transparent electrode was developed from silver nanowires (AgNWs) embedded in a colorless polyimide (cPI) by utilizing an inverted film-processing method. The resulting AgNW-cPI composite electrode had a transparency of >80%, a low sheet resistance of 8 Ω/□, and ultra-smooth surfaces comparable to glass. Leveraging the robust mechanical properties and flexibility of cPI, the thickness of the composite film was reduced to less than 10 µm, which is conducive to extreme flexibility. This film exhibited mechanical durability, for both outward and inward bending tests, up to a bending radius of 30 µm, while maintaining its electrical performance under cyclic bending (bending radius: 500 µm) for 100,000 iterations. Phosphorescent, blue organic light-emitting diodes (OLEDs) were fabricated using these composites as bottom electrodes (anodes). Hole-injection was poor, because AgNWs were largely buried beneath the composite's surface. Thus, we used a simple plasma treatment to remove the thin cPI layer overlaying the nanowires without introducing other conductive materials. As a result, we were able to finely control the flexible OLEDs' electroluminescent properties using the enlarged conductive pathways. The fabricated flexible devices showed only slight performance reductions of <3% even after repeated foldings with a 30 µm bending radius.

Enhancement of Characteristics of a Touch Sensor by Controlling the Multi-Layer Architecture of a Low-Cost Metal Mesh Pattern.

In this study, the characteristics of a metal mesh touch sensor were enhanced by optimizing the multi-layer architecture of the metal mesh pattern. Low-cost metal such as an aluminum (Al) layer was mainly applied to the architectures for practical applications in touch screen panel (TSP) industries. As well, molybdenum (Mo) was added to the architectures in order to minimize the drawbacks of Al. Three types of Mo/Al, Al/Mo and Mo/Al/Mo layers were fabricated by DC sputtering. The thickness of the Al and Mo layer was optimized at 150 and 30 nm, respectively. Low sheet resistance below 0.27 Ω/square was achieved with good adhesion on a glass substrate. Especially, in the case of architectures in which the Al layer was covered with an Mo layer, thermal stability and corrosion resistance was enhanced. The change in resistance of the Mo/Al/Mo architecture was less than 0.056 even after heat-treatment at 260 °C. By using the optimized layer architecture, the mesh pattern with a 4 µm line width showed good optical transmittance (86.7%) and reflectivity (13.1%) at 550 nm, respectively. Also, a touch sensor fabricated by using the Mo/Al/Mo mesh pattern operated well indicating that the mesh pattern is feasible in a TSP application.

Effect of Ag nanowire addition into nanoparticle paste on the conductivity of Ag patterns printed by gravure offset method.

This paper focuses on the effect of Ag nanowire addition into a commercial Ag nanopaste and the printability evaluation of the mixed paste by the gravure offset printing methodology. Ag nanowires were synthesized by a modified polyol method, and a small amount of them was added into a commercial metallic paste based on Ag nanoparticles of 50 nm in diameter. Two annealing temperatures were selected for comparison, and electrical conductivity was measured by four point probe method. As a result, the hybrid mixture could be printed by the gravure offset method for patterning fine lines up to 15 µm width with sharp edges and scarce spreading. The addition of the Ag nanowires was significantly efficient for enhancement of electrical conductivity of the printed lines annealed at a low temperature (150 degrees C), while the effect was somewhat diluted in case of high temperature annealing (200 degrees C). The experimental results were discussed with the conduction mechanism in the printed conductive circuits with a schematic description of the electron flows in the printed lines.

Microwave annealing of indium tin oxide nanoparticle ink patterned by ink-jet printing.

Indium tin oxide (ITO) is one of the most widely used transparent conducting oxides because of its two chief properties, electrical conductivity and optical transparency, as well as the ease with which it can be deposited as a thin film. In this study, we fabricated the ITO nanoparticles, and dispersed them in an organic mixture of liquid to make a solution for printing. The solution was ink-jet printed on a glass, and we employed microwave heating technology to make the ITO coated layer conductive and transparent. Microwave technology uses electromagnetic waves that pass through material and cause its molecules to oscillate, generating heat. It generates heat within the material and heats the entire volume at about the same rate. The ITO layers could be successfully annealed by the microwave irradiation, which is resulted in the sheet resistance of 365 ohm/sq and the transmittance of 84% within only 15 min of heating.

Application of rapid milling technology for fabrication of SiC nanoparticles.

SiC nanoparticles were successfully fabricated by a high energy ball milling method, so that can be used in the printed electronics to make SiC thin film patterns. Here we utilized the waste of Si sludge for making the SiC nanoparticles. In order to achieve uniform thin film from the nanoparticle ink, fine sized SiC nanoparticles less than 100 nm has to be uniformly dispersed. In this study, we employed the ultra apex milling (UAM) system for particle comminution and dispersion. We investigated the effects of milling parameters, e.g., size of ZrO2 bead and milling time. The size of the SiC particles reached about 103 nm after 4 hours of UAM, when the ZrO2 beads of 50 microm were used. Then SiC ink was formulated with organic solvents and a dispersing agent. A specially designed pattern was printed by an ink-jet printer for evaluating the feasibility of the SiC nanoparticle inks.

Synthesis of Ag nanowires for the fabrication of transparent conductive electrode.

Recently, advances in nano-materials research have opened the door for various transparent conductive materials, which include CNTs, graphene, Ag and Cu nanowires, and printable metal grids. Among them, Ag nanowires are particularly interesting to synthesize because bulk Ag exhibits the highest electrical conductivity among all metals. We tried to synthesize the Ag nanowires with a small diameter and long length, resulting in large aspect ratios. For the synthesis of the Ag nanowires, effects of various experimental parameters, i.e., the reaction time for synthesis, molar ratio of Ag source to surfactant, and molar weight of the surfactant were investigated with the physical shape of synthesized products. The Ag nanowire suspensions were formulated with the synthesized Ag nanowires, and a bar coating method with a Meyer rod was used to fabricate the transparent and conductive film on a glass substrate. For the thinnest wet coating, the transparent conductive layer of 90.6% transmittance at 550 nm of light wavelength and 66 ohm/sq sheet resistance could be obtained, while 13 ohm/sq was achieved at the transmittance of 76%.

Fabrication of SiC nanoparticles by physical milling for ink-jet printing.

Here we tried to show the possibility of mechanical milling method for fabrication of SiC nanoparticles and ink-jet printing method to make SiC patterns for use as several applications, e.g., micro hotplates. Planetary milling was employed to fabricate the nano-scale SiC particles from coarse powders. After 100 hours of milling, the size of the SiC particles decreased to about 100 nm, which was sufficient for the formulation of ink for ink-jet printing. The SiC particles were dispersed in an ink system consisted of ethylene glycol and ethanol with a small amount of additives. The ink with SiC nanoparticles could be successfully printed on an alumina substrate by the ink-jet printing method.

Synthesis of Cu nanoparticles with self-assembled monolayers via inert-gas condensation.

Cu nanoparticles with vaporized self-assembled monolayers (SAMs) for the prevention of oxidation were synthesized via inert-gas condensation (IGC). When processing the nanoparticles, the convection in the vacuum chamber was controlled using carrier gases such as Ar and He. Cu shots (2-8 mm) were used as raw materials and were evaporated via resistance heating. Octanethiol (CH3(CH2)7SH) was used for the SAMs and was introduced with the carrier gases during the process. The prepared samples were examined via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine the particle sizes, the coating thicknesses of the SAMs, and the particle distribution states. The ingredients were confirmed via X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectroscopy (EDS). The particle size and morphology were controlled by introducing various combinations of carrier gases, such as He, Ar and H2. Finally, stabilized Cu nanoparticles stably coated with octanethiol were successfully fabricated.