Youngho Jin

Bio: Youngho Jin is an academic researcher from Agency for Defense Development. The author has contributed to research in topics: Nanocomposite & Dielectric. The author has an hindex of 5, co-authored 18 publications receiving 158 citations. Previous affiliations of Youngho Jin include Georgia Institute of Technology & Korea Military Academy.

Enhanced dielectric properties of polymer matrix composites with BaTiO3 and MWCNT hybrid fillers using simple phase separation

Abstract: Poly (vinylidene fluoride) (PVDF) matrix hybrid nanocomposites, featuring ferroelectric barium titanate (BT) nanoparticles and multi-walled carbon nanotubes (MWCNT) embedded in the polymer, were fabricated by a miscible-immiscible coagulation method followed by hot pressing. SEM images showed good distribution of the ceramic nanoparticles with very little particle agglomeration. The conductive MWCNT increased the charge storage ability of the matrix polymer by serving as a polarized charge transport phase for the ferroelectric nanoparticles, while the small MWNT amounts used prevented the formation of conductive networks. The simple processing method utilized resulted in composites with high real permittivity and low dielectric loss over a wide range of frequency (10–1 MHz). The dielectric properties of the polymer matrix nanocomposites with hybrid fillers (BT with and without MWNT) were improved by optimizing the synergistic effects between the charge storage behavior of the ferroelectric phase and the charge transport behavior of the conductive phase. The best combination of real permittivity and dielectric loss properties (71.7 and 0.045 respectively) were obtained for the nanocomposites containing 37.1 vol% of BaTiO3 and 3 vol% of MWCNT. In addition to achieving reliable dielectric properties, the nanocomposites also displayed flexibility making these composites potentially useful for many flexible electronic devices and electrostatic energy storage devices.

Functionalized Polyurethane‐Coated Fabric with High Breathability, Durability, Reusability, and Protection Ability

Abstract: Transmission of pathogens via respiratory droplets can spread infections such as COVID‐19 Wearing a mask hinders the spread of COVID‐19 infection and has become mandatory in some cases Although most masks are affordable and disposable, continual daily replacement is required due to their performance deterioration caused by washing and contamination Hence, a urethane‐reactive coating material comprising perfluoro‐tert‐butanol‐hexamethylene diisocyanate is developed with highly hydrophobic and oleophobic properties to functionalize a polyurethane‐coated fabric to bestow high breathability, durability, reusability, and protection ability Its functions are maintained after scratch and wash testing, and its air permeability and water vapor transmittance rate (necessary for respiration) are unaffected Its filtration efficiency of water droplets containing 100 nm polystyrene particles (similar in size to SARS‐CoV‐2) is increased due to its highly hydrophobic properties In addition, it inhibits the adsorption of bovine serum albumin, the spike protein of COVID‐19, and Staphylococcus aureus and Pseudomonas aeruginosa [ABSTRACT FROM AUTHOR] Copyright of Advanced Functional Materials is the property of John Wiley & Sons, Inc and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission However, users may print, download, or email articles for individual use This abstract may be abridged No warranty is given about the accuracy of the copy Users should refer to the original published version of the material for the full abstract (Copyright applies to all Abstracts )

Dielectric liquid-based self-operating switch triboelectric nanogenerator for current amplification via regulating air breakdown

Abstract: Triboelectric nanogenerators (TENG) can harvest mechanical energy by using the displacement current generated by a time-variant electric field. Owing to the simple fabrication, low cost, and the suitability of a wide range of materials for such devices, TENGs can be used as a power source for self-powered systems and existing portable electronics. Nevertheless, the generation mechanism of TENGs must be optimized to overcome the current limitations caused by the air breakdown on triboelectric materials. Therefore, a dielectric liquid-based self-operating switch triboelectric nanogenerator (DLSS–TENG) was created, which can control the field emission on the electrode surface through the movement of the dielectric liquid. The movement of the dielectric material plate regulates the air breakdown by acting as a self-operating switch, which can enhance the current output of the TENG. Because dielectric liquids exhibit a large Debye length, which screens the electrostatic charge, they can be used to generate a distinctively high electrical output. The DLSS–TENG can charge a commercial capacitor by generating a closed-circuit current of up to 56 mA and open-circuit voltage of 100 V for a 0.5 Hz low-frequency mechanical input. The generation mechanism of the proposed DLSS–TENG can overcome the current electrical limitation by regulating the air breakdown.

Prediction of the percolation threshold and electrical conductivity of self-assembled antimony-doped tin oxide nanoparticles into ordered structures in PMMA/ATO nanocomposites.

Abstract: Electrical percolation in nanocomposites consisting of poly(methyl methacrylate) (PMMA) and antimony tin oxide (ATO) nanoparticles was investigated experimentally using monosize and polydisperse polymer particles. The nanocomposites were fabricated by compression molding at 170 °C. The matrix PMMA was transformed into space filling polyhedra while the ATO nanoparticles distributed along the sharp edges of the matrix, forming a 3D interconnected network. The measured electrical resistivity showed that percolation was achieved in these materials at a very low ATO content of 0.99 wt % ATO when monosize PMMA was used, whereas 1.48 wt % ATO was needed to achieve percolation when the PMMA was polydispersed. A parametric finite element approach was chosen to model this unique microstructure-driven self-assembling percolation behavior. COMSOL Multiphysics was used to solve the effects of phase segregation between the matrix and the filler using a 2D simplified model in the frequency domain of the AC/DC module. It...

Zr(OH)4/GO Nanocomposite for the Degradation of Nerve Agent Soman (GD) in High-Humidity Environments.

Abstract: Zirconium hydroxide, Zr(OH)4 is known to be highly effective for the degradation of chemical nerve agents Due to the strong interaction force between Zr(OH)4 and the adsorbed water, however, Zr(OH)4 rapidly loses its activity for nerve agents under high-humidity environments, limiting real-world applications Here, we report a nanocomposite material of Zr(OH)4 and graphene oxide (GO) which showed enhanced stability in humid environments Zr(OH)4/GO nanocomposite was prepared via a dropwise method, resulting in a well-dispersed and embedded GO in Zr(OH)4 nanocomposite The nitrogen (N2) isotherm analysis showed that the pore structure of Zr(OH)4/GO nanocomposite is heterogeneous, and its meso-porosity increased from 0050 to 0251 cm3/g, compared with pristine Zr(OH)4 prepared Notably, the composite material showed a better performance for nerve agent soman (GD) degradation hydrolysis under high-humidity air conditions (80% relative humidity) and even in aqueous solution The soman (GD) degradation by the nanocomposite follows the catalytic reaction with a first-order half-life of 60 min Water adsorption isotherm analysis and diffuse reflectance infrared Fourier transform (DRIFT) spectra provide direct evidence that the interaction between Zr(OH)4 and the adsorbed water is reduced in Zr(OH)4/GO nanocomposite, indicating that the active sites of Zr(OH)4 for the soman (GD) degradation, such as surface hydroxyl groups are almost available even in high-humidity environments

Elastic Softening of Amorphous and Crystalline Li-Si Phases with Increasing Li Concentration: A First-Principles Study

Abstract: Knowledge of the elastic properties of Li–Si alloys as a function of Li concentration is crucial in the development of reliable deformation and fracture mechanics models for Si anodes in Li-ion batteries. Here, we have studied these properties using first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes. In the case of crystalline alloys, we present the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios. We find that while these moduli decrease in an approximately linear manner with increasing Li concentration leading to significant elastic softening (by about one order of magnitude) in both crystalline and amorphous systems, the Poisson's ratios remain in the range of 0.05–0.20 and 0.20–0.30 in the case of crystalline and amorphous systems, respectively. Further, for a given Li concentration, we find that the amorphous structures are elastically somewhat softer than their crystalline counterparts, the difference being more significant (about 30–40%) in Li-poor phases. Our results underscore the importance of including the concentration dependence of elastic constants in the analysis of stress and deformation fields during lithiation and de-lithiation of Si anodes.

Enhancement of the dielectric response in polymer nanocomposites with low dielectric constant fillers.

Abstract: In order to increase the dielectric constants of polymer-based dielectrics, composite approaches, in which inorganic fillers with much higher dielectric constants are added to the polar polymer matrix, have been investigated. However, high dielectric constant fillers cause high local electric fields in the polymer, resulting in a large reduction of the electric breakdown strength. We show that a significant increase in the dielectric constant can be achieved in polyetherimide nanocomposites with nanofillers whose dielectric constant can be similar to that of the matrix. The presence of nanofillers reduces the constraints on the dipole response to the applied electric field, thus enhancing the dielectric constant. Our results demonstrate that through nanostructure engineering, the dielectric constant of nanocomposites can be enhanced markedly without using high dielectric constant nanofillers.

Rosin modified cellulose nanofiber as a reinforcing and co-antimicrobial agents in polylactic acid /chitosan composite film for food packaging

Abstract: Cellulose nanofiber (CNF) was modified by rosin and used as a reinforcement filler within a polylactic acid (PLA) matrix. The resulting film was then coated with chitosan (CHT) to prepare a two-layer composite film for antimicrobial food packaging. The FT-IR spectra of rosin modified CNF (R-CNF) displayed a clear peak at 1730cm-1, which confirmed the successful esterification of CNF by rosin. The R-CNF showed a better dispersion in PLA matrix than CNF and the loading of R-CNF had a significant effect on the mechanical properties of the resulting film. A percolation network was formed when the R-CNF loading was 8%, where the composite film displayed optimum mechanical properties. The antimicrobial test showed that the R-CNF/PLA/CHT composite film exhibited excellent antimicrobial performance against E. coli and B. subtilis, which could be attributed to the synergistic antimicrobial effect of CHT and rosin.

Improved dielectric, tensile and energy storage properties of surface rubberized BaTiO3/polypropylene nanocomposites

Abstract: The low permittivity of the polypropylene (PP) film has become a barrier for the further development of film capacitors with high energy storage density. An advanced strategy of the high-permittivity filler/polymer nanocomposite turns out to be a promising way of solving this problem. In this work, we coated ethylene propylene diene monomer (EPDM) as the shell on the surfaces of BaTiO3 successfully to fabricate core-shell structural nanoparticles. The addition of surface rubberized BaTiO3 into PP matrix promotes the permittivity to about 5.8, while the dielectric loss is barely changed as compared with PP itself. In addition, the elongation at break is as high as 364%, which is over 4 times higher than that of PP. The influences of shell thickness (3 nm, 5 nm and 7 nm) for the nanoparticles and hot-stretching process for the nanocomposite films were also carefully investigated, both of which greatly affected the properties of nanocomposites. Finally, the optimum breakdown strength as high as 370 MV/m is obtained, leading to a maximum energy density of 3.06 J/cm3, which can be attributed to both high breakdown strength and high permittivity of the core-shell structural BaTiO3/PP nanocomposites.