Coloration on Bluish Alginate Films with Amorphous Heterogeneity Thereof.

Using sodium alginate (Alg) aqueous solution containing indigo carmine (IdC) at various concentrations we characterized the rippled surface pattern with micro-spacing on a flexible film as intriguing bluish Alg-IdC iridescence. The characterization was performed using Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, field emission scanning electron microscopy, atomic force microscopy, electron microscopy, differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction analysis, and photoluminescence detection. The edge pattern on the film had a maximum depth of 825 nm, a peak-to-peak distance of 63.0 nm, and an average distance of 2.34 nm. The center of the pattern had a maximum depth of 343 nm and a peak-to-peak distance of 162 nm. The pattern spacing rippled irregularly, widening toward the center and narrowing toward the edges. The rippled nano-patterned areas effectively generated iridescence. The ultraviolet absorption spectra of the mixture in the 270 and 615 nm ranges were the same for both the iridescent and non-iridescent film surfaces. By adding Ag+ ions to Alg-IdC, self-assembled microspheres were formed, and conductivity was improved. Cross-linked bluish materials were immediately formed by the addition of Ca2+ ions, and the film was prepared by controlling their concentration. This flexible film can be used in applications such as eco-friendly camouflage, anti-counterfeiting, QR code materials for imaging/sensing, and smart hybrid displays.

Crack Detecting Method Based on Grid-Type Sensing Networks Using Electrical Signals.

Cracks have a primary effect on the failure of a structure. Therefore, the development of crack sensors with high accuracy and resolution and cracks detection method are important. In this study, the crack sensors were fabricated, and the crack locations were detected with the electrical signal of the crack sensor. First, a metal grid-type micro-crack sensor based on silver was fabricated. The sensor is made with electrohydrodynamics (EHD) inkjet printing technology, which is well known as the next generation of printed electronics technology. Optimal printing conditions were established through experiments, and a grid sensor was obtained. After that, single cracks and multiple cracks were simulated on the sensor, and electrical signals generated from the sensor were measured. The measured electrical signal tracked the location of the cracks in three steps: simple cross-calculation, interpolation, and modified P-SPICE. It was confirmed that cracks could be effectively found and displayed using the method presented in this paper.

Evaluation of Temperature Sensors for Detection of Heat Sources Using Additive Printing Method.

Electrohydrodynamic (EHD) inkjet printing is an efficient technique for printing multiple sensors in a multifaceted area. It can be applied to various fields according to the shape of the printing result and the algorithm employed. In this study, temperature sensors capable of detecting heat sources were fabricated. Inks suitable for EHD inkjet printing were produced, and optimal parameters for printing were determined. Printing was performed using the corresponding parameters, and various printing results were obtained. Furthermore, an experiment was conducted to confirm the temperature measurement characteristics of the results and the tolerance of the sensor. Grid-type sensors were fabricated based on the results, and the sensor characteristics were confirmed in an orthogonal form. Heat was applied to arbitrary positions. Resistance to changes due to heat was measured, and the location at which the heat was generated was detected by varying the change in resistance. Through this study, efficient heat control can be achieved, as the location of the heat source can be identified quickly.

Fabrication of innocuous hydrogel scaffolds based on modified dextran for biotissues.

Substrates with basic structures similar to those of living tissues are useful as cellular scaffolds for the preparation of biocompatible and innocuous materials. In this study, a hydrogel matrix was prepared by introducing a functional group capable of forming crosslinks between natural polymers to create a basis for preparing a microenvironment favorable for cell adaptation. The modified dextran hydrogel polymer was designed to mimic the conditions of the extracellular matrix (ECM) as a scaffold. The precursors of the target hydrogel were synthesized using condensation with a stepwise procedure. A delicate hydrogel based on modified dextran was obtained via photo-crosslinking under room temperature at UV-254 nm. The biocompatibility of this hydrogel was verified using green fluorescence images acquired by incubating a cell line. The characteristics of the hydrogel were verified using proton nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD) analysis, and electrostatic spinning. The crosslinked structure and biocompatibility of the modified hydrogel were confirmed using instrumental analyses and a promising cell culture. Using TGA, the weight losses of precursor and hydrogel were determined to be 90.96% and 39.2%, respectively, up to 600 °C. The diameters of the nanofibers, fabricated via electrospinning, were measured to range from 200 to 500 nm.

Temperature-Sensing Inks Using Electrohydrodynamic Inkjet Printing Technology.

Temperature measurement is very important for thermal control, which is required for the advancement of mechanical and electronic devices. However, current temperature sensors are limited by their inability to measure curved surfaces. To overcome this problem, several methods for printing flexible substrates were proposed. Among them, electrohydrodynamic (EHD) inkjet printing technology was adopted because it has the highest resolution. Since EHD inkjet printing technology is limited by the type of ink used, an ink with temperature-sensing properties was manufactured for use in this printer. To confirm the applicability of the prepared ink, its resistance characteristics were investigated, and the arrangement and characteristics of the particles were observed. Then, the ink was printed using the EHD inkjet approach. In addition, studies of the meniscus shapes and line widths of the printed results under various conditions confirmed the applicability of the ink to the EHD inkjet printing technology and the change in its resistance with temperature.

Resistances of Carbon Black and Polymers in Smart Paints for Temperature Sensors.

Temperature sensing and control is an important factor to prevent the overheating of mechanical and electrical components in various devices. However, commercialized temperature sensors can be disadvantageous due to their limited shapes. Therefore, we propose a smart paint to solve this issue. In this study, smart paints were produced based on carbon black, and their properties were measured using thermistors. Experiments were conducted to analyze the resistance properties using carbon and four types of polymers. Through the scanning electron microscopy (SEM) images of the mixed paints, it was shown that the resistances were decreased due to the necking phenomena. Furthermore, each paint provides a different temperature coefficient depending on the polymer type.

Biomimetic Crack Sensors Using Electrohydrodynamic Technology.

This paper proposes a new mechanism for detecting microscopic damage of structures based on imitating the sensory organs of spiders. Therefore, it is essential to manufacture sensors that can react sensitively to the micro deformations of structures. Numerous cracks were intentionally generated to improve the sensitivity of the proposed sensor, and an increase in the gap of the crack was observed by scanning electron microscopy (SEM) observation. Electrohydrodynamic technology is used to detect deformations in a structure of depositing Ag nano paste on a polyethylene terephtha-late (PET) substrate. Ag nano lines are also observed by SEM images. The sensor is constructed as a grid structure, by forming layers patterned horizontally and vertically. An impact tester is used to verify the mechanism for structural health monitoring using the developed sensor. The resistance changes of the sensors are applied to estimate the structure's damaged location. The intersections of the lines with varying resistance can be used to accurately detect crack initiation. The proposed mechanism is a powerful methodology for estimating and detecting microscopic deformations and damage to structures.

Sensing Characteristics of Improved Positive Temperature Coefficient Thermistors with Paint Forms.

The disadvantage of using a typical temperature sensor is limited depending on the shape of the model to be measured. If the shape is curved, it is not easy to check the surface temperature. A smart paint for temperature measurement is proposed to overcome this disadvantage. Polymer solutions were prepared with a dispersion of materials and viscosity with the properties of paint forms. The smart paints showed various sensing characteristics depending on the amount of materials. In addition, it was analyzed through the scanning electron microscopy (SEM) that sliver particles are disposed around the ceramic particles to have electrical conductivity. This study optimized the proportion of ceramics added to smart paints so that they could overcome the limitations of PTC thermistors that can only identify specific temperatures. Therefore, the developed paint-type temperature sensor makes it easy to measure the temperature of various models.

Biomimetic Structural Coloration Based on Spherical Silica Nanoparticles.

Structural colors based on nanostructured surfaces are an environmentally friendly alternative to dyes and pigments. In this study, structural colors were produced by spherical silica nanoparticles. By controlling the size of the spherical silica nanoparticles, the changes in color were controlled. The sizes of the nanoparticles were controlled by adjusting the ammonia content in the conventional Stöber method. Spherical silica nanoparticle powders were obtained using a centrifuge and an ultrasonic grinder oven, which were subsequently dispersed in deionized water and alcohol for dip coating. The particle sizes of the samples increased with increase in the amount of ammonia used in the synthesis process and were not affected by the dip coating. Spherical silica nanoparticles were uniformly arranged on the surface of the glass slides for all the samples studied. Thus, the structural colors produced by the spherical silica nanoparticles changed according to the particle size, which can be controlled by the ammonia content during synthesis.

Fracture Surface of 3D Printed Honeycomb Structures at Low Temperature Environments.

In this paper, surface characteristics of 3D printed structures fractured at low temperature environments are analyzed. The samples are fabricated by using ABS (acrylonitrile butadiene styrene copolymer) material, and the structures are constructed by the well-known honeycomb models using a FDM-Type 3D printer. To analyze the fracture surface of the samples constructed uniquely by using the 3D printer, the bending loads are applied to the samples at 30, -10 and -50 °C, respectively. The characteristics of the fracture surfaces of the 3D samples are also observed by the FE-SEM (field emission scanning electron microscope) equipment. From this experiment, it is evaluated that the fractured surface of the 3D sample is very rough at 30 °C, while it is smooth at a relatively low temperature. Also, several unique features of the fracture surface of a 3D printed sample structured by honeycomb models are also examined.

Resistance Characteristics and Particle Arrangement of Smart Paint for Surface Temperature Sensor.

There are limitations on the shape of models that can be measured with commonly used temperature sensors. These disadvantages are difficult to measure temperatures of the curved surface. To overcome the shortcomings, a smart paint for temperature measurement is proposed in this work. A polymer solution was prepared for viscosity of the paint and dispersion of materials. The BaTiO3 and Ag nanopaste are used for PTC characteristics and conductivity of the paint, respectively. Smart paint were analyzed the arrangement and shape of particles according to the processes and production methods. Also, the change of resistance was measured while increasing the temperature. The results show that resistance increased as the temperature increased. The performance of the manufactured smart paint was confirmed as a surface temperature sensor.

Micropatterning of Metal-Grid Micro Electro Mechanical Systems (MEMS) Sensor for Crack Detection Using Electrohydrodynamic Printing System.

In this paper, a mechanism of sensors for micro crack detection is proposed according to circuit disconnection. In order to detect micro cracks, sensitive sensors based on micropatterning using a electrohydrodynamic (EHD) technology are necessary. For EHD printing, it is essential to find an optimum condition between ink materials and environmental parameters. Therefore, the distribution of the jetting mode between the flow rate and the voltage is confirmed through experiments. Metal-grid was patterned and resistance of each circuit by crack occurrence was measured. The resistance changes are occurred at the position where the crack is generated, and the crack position can be estimated with grid type sensors. The resistance in the cracked circuits are relatively larger than it in non-cracked circuits. It was confirmed that micro cracks were well detected by using the proposed crack sensors and mechanisms.