TPMS-based auxetic structure for high-performance airless tires with variable stiffness depending on deformation.

A novel auxetic structure applicable to airless tire spokes is designed based on the primitive-type triply periodic minimal surface (P-TPMS) to have higher stiffness through deformation under compressive force. For becoming higher stiffness by deformation, an unit cell of auxetic structure is proposed and its characteristics according to design parameters are studied. Based on the parametric study, a rotated primitive-type auxetic structure (RPAS) is designed, and the deformative behaviors of an airless tire with the RPAS spokes are compared with a generally used honeycomb spoke. Simulation and experiment results show that the designed RPAS tire exhibits more stable behavior through higher rigidity depending on the deformation state when compressed on flat ground and obstacles. This variable stiffness characteristic of RPAS tires can be advantageous for shock absorption and prevention of large local deformations. Also, the manufacturability of the designed auxetic structure is evaluated using real rubber-based additive manufacturing processes for practical application in the tire manufacturing industry.

Design and evaluation of additive manufactured highly efficient inclined-wing type continuous mixer.

We develop a novel milli-scale mixer (tilted-wings mixing unit, TWM unit) based on the design for additive manufacturing (DfAM). The proposed tilted-wings mixer has basically designed to have three separate wings that split and combine fluids in order to mix together effectively. Its structure is simple for easy fabrication: two major design parameters of angle among three wings and connecting angle between tilted-unit, which are optimized using the computational fluid dynamics (CFD) analysis. From the CFD analysis, we obtain the best-combined mixing module from analyses of various combinations of TWM units for a highly effective mixing ratio. The mixing ratio of three combined units reaches near 100%, which is validated by the experiment and analysis. We believe that the proposed milli-scale mixer can be utilized in diverse chemical continuous mixers and reactors for minimizing of use of chemicals that can pollute the environment.

Nanopattern-Embedded Micropillar Structures for Security Identification.

A novel method was developed for fabricating nanopatterns embedded on micropillar-structured surfaces using nanowelding technology for security identification. Commonly used substrates, that is, polyethylene films, glass wafers, Si wafers, and curved surfaces, were employed and their characteristics were evaluated. Cr was deposited onto the selected substrate to strengthen the adhesion force, and an adhesive layer of ultra-thin metal was deposited on top of the Cr layer. Lastly, nanopatterns were embedded on the substrates by nanowelding. The morphologies, cross sections, and three-dimensional (3D) images of the fabricated nanostructures were evaluated, and their crystalline structures and compositions were analyzed. Using the same method, nanopatterns embedded on micropillar-structured surfaces were fabricated for the first time as security patterns to improve security identification. The fabricated security patterns were characterized in three stages. First, micropillar structures and structural color were simply observed via optical microscopy to achieve a preliminary judgment. The appearance of structural color was due to the nanostructures fabricated on the micropillar surface. Next, the designed nanopatterns on the micropillar-structured surfaces were observed by scanning electron microscopy. Lastly, the changes in the spectral peaks were precisely observed using a spectrometer to achieve an enhanced security pattern. The fabricated security patterns can be suitable for valuable products, such as branded wines, watches, and bags. In addition, the proposed method offers a simple approach for transferring metal nanopatterns to common substrates. Moreover, the fabricated security patterns can have potential applications in semiconductor electrodes, transparent electrodes, and security identification codes.

Heterogeneous Nanostructures Fabricated via Binding Energy-Controlled Nanowelding.

A novel concept for fabricating heterogeneous nanostructures based on different melting temperatures is developed. Au-Ag composite cross-structures are fabricated by nanowelding technologies. During the fabrication of Au-Ag composite cross-structures, Ag nanowires transform into ordered particles decorating the Au nanowire surfaces with an increase in the welding temperature because of the different melting temperatures of Au and Ag. To compare and explain the melting temperatures, the thicknesses of Au and Ag nanowires as parameters are analyzed. Scanning electron microscopy and focused ion beam imaging are used to observe the morphologies and cross sections of the fabricated samples. The evolution of 3D nanostructures is observed by atomic force microscopy, whereas the compositions and binding energies of the nanostructures are determined by X-ray diffraction and X-ray photoelectron spectroscopies. In addition, the atomic structures are analyzed by transmission electron microscopy, and the optical properties of the fabricated nanostructures are evaluated by spectrometry. Furthermore, color filter electrodes are fabricated, and their polarization properties are evaluated by sheet resistance measurements and observing the color and brightness of light-emitting diodes. The proposed method is suitable for application in various fields such as biosensors, optics, and medicine.

Eight Inch Wafer-Scale Flexible Polarization-Dependent Color Filters with Ag-TiO2 Composite Nanowires.

In this study, 8 in. wafer-scale flexible polarization-dependent color filters with Ag-TiO2 composite nanowires have been fabricated using nanoimprint and E-beam evaporation. The filters change their color via a simple rotation of the polarizer. In addition, the color of the filter can be controlled by altering the thickness of the Ag and TiO2 nanowires deposited on the polymer patterns. Polarization-dependent color filters were realized by selective inhibition of transmission using the plasmonic resonance at the insulator/metal/insulator nanostructure interface, which occurs at particular wavelengths for the transverse magnetic polarizations. Special colors, including purple, blue, green, yellow, and pink, could be obtained with high transmission beyond 65% by varying the thickness of the deposited Ag and TiO2 nanowires on the periodic polymer pattern under transverse magnetic polarization. In addition, a continuous color change was achieved by varying the polarization angle. Last, numerical simulations were implemented in comparison with the experimental results, and the mechanism was explained. We believe that this simple and cost-effective method can be applied to processes such as anticounterfeiting and holographic imaging as well as to color displays.

Shape-Controlled 3D Periodic Metal Nanostructures Fabricated via Nanowelding.

A novel method for fabricating 3D metallic nanostructures to be used in polarized color filters based on nanoimprint lithography, electron-beam evaporation, and nanowelding is proposed. The shape of the nanostructures can be controlled by adjusting the temperature for the nanowelding process. Ag nanowires deposited on polymer patterns are accumulated by the nanowelding process to build up diverse 3D nanostructures. The morphologies of the fabricated 3D nanostructures are analyzed using scanning electron microscopy, atomic force microscopy, and focused ion beam; the heating temperature is varied from 90 to 130 °C in steps of 10 °C. In order to analyze the recrystallization phenomenon after welding, transmission electron microscopy is utilized. The 3D metallic nanostructure has different morphologies and optical properties corresponding to welding temperature conditions and accumulated layer thicknesses. Based on preliminary experimental results, the process parameters are optimized and a polarized color filter is fabricated. Optical characteristics of the filter are evaluated using polarizer and spectrometer. Through this work, it is shown that the proposed method is an effective way to realize various 3D metallic nanostructures for special optical properties, therefore the method based on nanowelding can be utilized in fabrication of functional metamaterials, optical filters, biosensors, and others.

Three-dimensional plasmonic Ag/TiO2 nanocomposite architectures on flexible substrates for visible-light photocatalytic activity.

In this study, a periodic three-dimensional (3D) Ag/TiO2 nanocomposite architecture of nanowires was fabricated on a flexible substrate to enhance the plasmonic photocatalytic activity of the composite. Layer-by-layer nanofabrication based on nanoimprint lithography, vertical e-beam evaporation, nanotransfer, and nanowelding was applied in a new method to create different 3D Ag/TiO2 nanocomposite architectures. The fabricated samples were characterized by scanning electron microscopy, transmission electron microscopy, focused ion-beam imaging, X-ray photoelectron spectrometry, and UV-visible spectroscopy. The experiment indicated that the 3D nanocomposite architectures could effectively enhance photocatalytic activity in the degradation of methylene blue solution under visible light irradiation. We believe that our method is efficient and stable, which could be applied to various fields, including photocatalysis, solar energy conversion, and biotechnology.

Frictional response of normal and osteoarthritic articular cartilage in human femoral head.

We evaluated the microscale frictional response of human articular cartilage in different osteoarthritis stages using an atomic force microscope. Four human femoral heads (60-80 years old) with different osteoarthritis stages were explanted, and two cylindrical cartilage samples were sectioned from each femoral head. The microscale frictional coefficient mu of human cartilage in phosphate-buffered saline increased with increasing osteoarthritis stages, resulting in mu = 0.119 +/- 0.036 for stage 0 (normal cartilage), 0.151 +/- 0.039 for stage I, 0.158 +/- 0.041 for stage 2, and 0.409 +/- 0.119 for stage 3. Statistically significant differences of mu values for different osteoarthritis stages were detected only between stage 3 and other stages (p < 0.0001). The average surface roughness Rq significantly increased with increasing osteoarthritis stages, ranging from 137 +/- 25 nm for stage 0 to 533 +/- 196 nm for stage 3. A significant correlation between mu and Rq for different osteoarthritis stages was observed (R2 = 0.981). These results demonstrate a positive correlation between the osteoarthritis stages and cartilage surface roughness, and the dependence of the human cartilage frictional response, on osteoarthritis progression. The results could be due to a decrease in the superficial zone protein concentration during the natural progression of osteoarthritis.

Design and performance evaluation of a rotary magnetorheological damper for unmanned vehicle suspension systems.

We designed and validated a rotary magnetorheological (MR) damper with a specified damping torque capacity, an unsaturated magnetic flux density (MFD), and a high magnetic field intensity (MFI) for unmanned vehicle suspension systems. In this study, for the rotary type MR damper to have these satisfactory performances, the roles of the sealing location and the cover case curvature of the MR damper were investigated by using the detailed 3D finite element model to reflect asymmetrical shapes and sealing components. The current study also optimized the damper cover case curvature based on the MFD, the MFI, and the weight of the MR damper components. The damping torques, which were computed using the characteristic equation of the MR fluid and the MFI of the MR damper, were 239.2, 436.95, and 576.78 N·m at currents of 0.5, 1, and 1.5 A, respectively, at a disk rotating speed of 10 RPM. These predicted damping torques satisfied the specified damping torque of 475 N·m at 1.5 A and showed errors of less than 5% when compared to experimental measurements from the MR damper manufactured by the proposed design. The current study could play an important role in improving the performance of rotary type MR dampers.

Fabrication of nano- and micro-scale UV imprint stamp using diamond-like carbon coating technology.

Two-dimensional (2-D) and three-dimensional (3-D) diamond-like carbon (DLC) stamps for ultraviolet nanoimprint lithography were fabricated with two methods: namely, a DLC coating process, followed by focused ion beam lithography; and two-photon polymerization patterning, followed by nanoscale-thick DLC coating. We used focused ion beam lithography to fabricate 70 nm deep lines with a width of 100 nm, as well as 70 nm deep lines with a width of 150 nm, on 100 nm thick DLC layers coated on quartz substrates. We also used two-photon polymerization patterning and a DLC coating process to successfully fabricate 200 nm wide lines, as well as 3-D rings with a diameter of 1.35 microm and a height of 1.97 microm, and a 3-D cone with a bottom diameter of 2.88 microm and a height of 1.97 microm. The wafers were successfully printed on an UV-NIL using the DLC stamps without an anti-adhesive layer. The correlation between the dimensions of the stamp's features and the corresponding imprinted features was excellent.