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March 2016 - present
Publications
Publications (110)
Efforts to mass-produce high-quality graphene sheets are crucial for advancing its practical and industrial applications across various fields. In this study, we present an innovative electrochemical exfoliation method designed to enhance graphene quality and increase yield. Our approach combines two key techniques: expanding the tightly packed gra...
Hydrogen represents a carbon-free and sustainable energy carrier. Electrochemical water splitting via hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a green approach for the hydrogen production.
Nevertheless, unfavorable thermodynamics and sluggish kinetics limit the water splitting efficiency. While the benchmark catalyst...
As a technique in artificial intelligence, a convolution neural network model has been utilized to extract average surface roughness from the geometric characteristics of a membrane image featuring micro- and nanostructures. For surface roughness measurement, e.g. atomic force microscopy and optical profiler, the previous methods have been performe...
The potential applications of epoxy-based solid polymer electrolytes are continually expanding because of their versatile characteristics. These characteristics include mechanical rigidity, nonvolatility, nonflammability, and electrochemical stability. However, it is worth noting that pure epoxy-based solid polymer electrolytes inherently exhibit l...
Designing an efficient and multifunctional electrocatalyst is central to hydrogen production technologies such as hydrogen evolution, oxygen evolution, and urea oxidation reactions (HER/OER/UOR). Herein, we report the synthesis of nickel...
Hydrogen represents a carbon-free and sustainable energy carrier. Electrochemical water splitting via hydrogen
evolution reaction (HER) and oxygen evolution reaction (OER) is a green approach for the hydrogen production.
Nevertheless, unfavorable thermodynamics and sluggish kinetics limit the water splitting efficiency. While the
benchmark catalyst...
Tuning the catalytic surface as well as interface of the electrocatalysts is central to the rational design of efficient electrocatalysts for hydrogen/oxygen evolution reactions (HER/OER). Herein, we report the polyaniline...
The use of graphene sheets as a reinforcing agent in polymeric nanocomposites is increasing owing to their exceptional mechanical and thermal properties. Herein, graphene oxide (GO) is used as the reinforcing material in natural rubber (NR)/GO elastomeric nanocomposites to enhance the mechanical and thermomechanical properties of the composites. NR...
Aramid nanofibers have recently been used as novel reinforcing materials to overcome the limitations of epoxy resin because of their superior strength and toughness. Until now, aramid nanofibers were hybridized into the epoxy resin by adding water into an aramid nanofiber solution to obtain free-standing powders. Unfortunately, such a water-based m...
As the number of enclosed residential buildings increases to minimize energy consumption, research on indoor air quality is becoming more important. Particulate matter (PM) generated during the cooking process in the kitchen, in particular, must be effectively removed because of rapid propagation to the room and harm to the human body. To remove th...
Engineering the conventional electrode designs as well as exploring prospective materials and prominent electrolytes, all of which are critically required to tackle the fundamental limitations associated with the current sustainable energy technologies. Structural supercapacitors (SSCs) have recently emerged as next-generation energy storage and co...
In the field of environment and building engineering, the airflow pattern is one of the main factors controlling the indoor environmental quality. The control of airflow patterns has been examined, yet it remains problematic owing to a number of factors related to the location of the air inlets and outlets, and distributions of the indoor pollutant...
In the study, a new method to enhance the performance of a thermoelectric generator (TEG) device by utilizing the water-film evaporative cooling is proposed. An experimental device was constructed by incorporating a water-film cooling pond with a commercially available TEG. Experiments were performed to investigate the effects of the main operating...
Microfluidic circuit on disk platform, also known as lab-on-a-disk, is an integrated system for automated high-throughput screening for biochemical analysis. The microfluidic circuit on disk is performing biochemical analysis through sequential processes such as filtration, separation, detection, and synthesis of reagents. Sequential processes in m...
Among various methods to produce graphene sheets, electrochemical exfoliation has been regarded as an effective method for the mass production of high-quality graphene sheets because of its simplicity and environmental friendliness. However, conventional electrochemical exfoliation has a disadvantage of accumulating intercalating ions at graphite i...
Ultra-sensitive amperometric glucose sensors were developed by the synergistic combination of one-dimensional silver nanowires (Ag-NWs) and two-dimensional graphene sheets in the form of highly porous three-dimensional nano-structures (3D NSs). To achieve this, a simple hydrothermal sol-gel technique was applied by establishing covalent crosslinks....
Three-dimensionally porous carbon nanostructures have been widely used in energy storage applications owing to their large specific surface areas and excellent electrical properties. In addition, copper oxide has been considered as an effective pseudocapacitive material to significantly increase the energy density. In this paper, we introduce the s...
Textile-based electronic devices should be not only bendable but also highly stretchable for human-friendly wearable electronic applications. Herein, a highly stretchable and mechanically durable fiber transistor was designed and prepared by combining all-stretchable electronic components. First, electrically conductive and stretchable electrodes w...
A fast-cure carbon fiber/epoxy prepreg was thermoformed against a replicated automotive roof panel mold (square-cup) to investigate the effect of the stacking sequence of prepreg layers with unidirectional and plane woven fabrics and mold geometry with different drawing angles and depths on the fiber deformation and formability of the prepreg. The...
Easy shapeable highly porous and robust three dimensional (3D) nano-carbon architectures (3D NCA) are crucial for the practical applications of electrochemical energy storage devices. Here, a facile easy shapeable nitrogen-doped graphene coated 3D NCA exhibiting an ultra-high specific surface area, remarkable robustness, and excellent aqueous wetta...
Nickel oxide has been widely used in chemical sensing applications, because it has an excellent p-type semiconducting property with high chemical stability. Here, we present a novel technique of fabricating three-dimensional porous nitrogen-doped nickel oxide nanosheets as a highly sensitive NO₂ sensor. The elaborate nanostructure was prepared by a...
To facilitate the immobilization of the silver nanoparticles with high crystallinity and stability, the mussel-inspired dopamine is functionalized on the surface of the graphene. Considering the unique adhesive property of a catechol group in the dopamine toward metallic ions, a large amount of silver nanoparticles can be coated on the surface of t...
A graphene/carbon nanotube hybrid material stabilized in an aqueous medium, was coated on carbon fibers by anodic electrophoretic deposition. Chemically oxidized graphene, graphene oxide, was used as a stabilizing agent for dispersion of carbon nanotubes and as a transport medium for the graphene oxide/carbon nanotube hybrid during electrophoretic...
In this work, tensile and in-plane shear tests for thermoplastic glass fiber/polypropylene composites were performed at a thermo-forming temperature and their properties were characterized and mathematically expressed by using the non-orthogonal constitutive model. As for the thermo-forming test, half-dome experiments were carried out by varying th...
Photochromic molecules have been recently adopted by many researchers for organic field-effect transistor (OFET) applications, since they offer the opportunity to achieve flexible-type ultraviolet (UV) light sensors with the advantages of organic material-based solution processes. Here, we present the novel usage of an azobenzene derivative in the...
Smart fabrics and interactive textiles have attracted great interest as a newly emergent material because of their multifunctional capabilities. Herein, a highly robust wireless flexible strain sensor on the basis of commercial textile by the integration of functional hybrid carbon nanomaterials and piezoresistive material is fabricated. Specifical...
Carbon fiber-reinforced thermoplastic composites have not been considered as constituent materials for structural parts due to the poor interfacial adhesion between the fiber and the thermoplastic matrix. In this work, polyamide 6 (PA6) composites with pitch carbon fibers (pCF) were fabricated by alternatively stacking PA6 films and pCF fabrics fol...
Here, an anodic electrophoretic deposition was adopted to facilitate the large-scale uniform coating of nano-fillers onto carbon fibers to enhance the interfacial properties between carbon fibers and epoxy matrix. As interface–reinforcing materials, aramid nanofibers were introduced because of their superior mechanical properties and epoxy matrix-f...
Highly flexible organic nanofiber phototransistors are fabricated on a highly flexible poly(ethylene terephthalate) (PET) textile/poly(dimethylsiloxane) (PDMS) composite substrate. Organic nanofibers are obtained by electrospinning, using a mixture of poly(3,3″′-didodecylquarterthiophene) (PQT-12) and poly(ethylene oxide) (PEO) as the semiconductin...
Based on mussel-inspired polydopamine (PDA), a novel technique to fabricate carbon nanowire (CNW) arrays is presented for a possible use of porous carbon electrode in electrochemical energy storage applications. PDA can give more porosity and nitrogen-doping effect to carbon electrodes, since it has high graphitic carbon yield characteristic and ri...
Mechanically robust, flexible, and electrically conductive textiles are highly suitable for use in wearable electronic applications. In this study, highly conductive and flexible graphene/Ag hybrid fibers were prepared and used as electrodes for planar and fiber-type transistors. The graphene/Ag hybrid fibers were fabricated by the wet-spinning/dra...
Carbon fiber reinforced composite has been a good candidate of lightweight structural component in the automotive industry. As fast production speed is essential to apply the composite materials for the mass production area such as automotive components, the high speed liquid composite molding processes have been developed. Fast resin injection thr...
Experimental considerations have been performed to obtain the high contrast optical microscopic images of graphene oxide sheets which are useful to probe their quality and morphological information such as a shape, a size, and a thickness. When graphene oxide is used as a semiconducting material in a silicon-based field effect transistor, it is nec...
Development of simple and efficient method for large-scale production of mechanically strong and electrically conductive graphene fiber is highly desirable for practical applications, such as fiber-reinforced composites, wearable electronics, and electromagnetic irradiation shielding. Here, we present a facile approach for the preparation of amine-...
Development of simple and efficient method for the large-scale production of gaphene/metal nanoparticle hybrids is highly desirable for practical applications, such as catalyst, energy generation and storage, optoelectronics, and sensors. Here, we present a facile approach for the preparation of graphene/gold nanoparticle (AuNP) hybrids by simply m...
Two-dimensional (2D) graphene sheets have become a versatile platform for the fabrication of innovative hybrid materials with various functions due to their unique electrical, optical, thermal, and mechanical properties. The preparation of graphene-based composites with nanoscale precision is highly important for reproducible and controllable perfo...
Mussel-inspired catecholamine polymers (polydopamine and polynorepinephrine) were coated on the surface of carbon and glass fibers in order to increase the interfacial shear strength between fibers and polymer matrix, and consequently the interlaminar shear strength of fiber-reinforced composites. By utilizing adhesive characteristic of the catecho...
Mussel-inspired catecholamine polymers (poly(dopamine) and poly(norepinephrine)) were coated on the surface of carbon and glass fibers in order to increase the interfacial shear strength between fibers and polymer matrix, and consequently the interlaminar shear strength of fiber-reinforced composites. By utilizing adhesive characteristic of the cat...
The performance of fiber-reinforced composites is governed not only by the nature of each individual component comprising the composite, but also by the interfacial properties between the fiber and the matrix. We present a novel layer-by-layer (LbL) assembly for the surface modification of glass fiber to enhance the interfacial properties between t...
Experimental considerations have been performed to obtain the clear optical microscopic images of graphene oxide which are useful to probe its quality and morphological information such as a shape, a size, and a thickness. In this study, we investigated the contrast enhancement of the optical images of graphene oxide after hydrazine vapor reduction...
The site-selective attachment of metal nanoparticles (NPs) on graphene surface is highly desirable for various applications such as electrochemical sensors and catalysts. Here, we present a simple and effective synthetic approach for the site-selective immobilization of gold NPs (AuNPs) on either basal planes or edges of graphene sheets. The basic...
This paper presents the slip behavior of composite fabrics by high speed resin flow in high pressure resin transfer molding. In order to observe the fiber deformation behavior, we constructed the measuring equipment for friction coefficient between fiber and mold, and the monitoring system for deformation of fiber preform in high-pressure RTM proce...
Short fiber reinforced composites have attracted industrial attention due to the comparable mechanical properties and good processability. In order to enhance the properties, proper surface treatment on the reinforcing fibers should be needed. In addition, the composites manufactured by injection molding have diverse fiber orientations variable wit...
Partially reduced graphene oxide (pRGO) was coated on carbon fibers by an anodic electrophoretic deposition (EPD). Coated-pRGO increased surface energy and wettability of carbon fiber. As a multi-functional sizing agent, pRGO enhanced both mechanical and electrical properties of the carbon fiber composite in spite of introducing a very small amount...
Simple and effective preparation methods for highly stacked graphene papers are presented by site-selective functionalization of graphene oxides with di-functional small molecules, 1,4-butandiol and ethylenediamine. It was found that hydroxyl groups of 1,4-butandiol react mostly with edges of graphene oxides, while more reactive amine groups of eth...
We report a facile green approach to the synthesis of silver nanoparticles (Ag NPs) on the surface of graphene oxide nanosheets functionalized with mussel-inspired dopamine (GO-Dopa) without additional reductants or stabilizers at room temperature. The resulting hybrid Ag/GO-Dopa exhibits good dispersity and excellent catalytic activity in the redu...
In order to numerically evaluate hydroformed DP-steel tubes on crash performance while considering weld-heat effects, finite element simulations of the crash were performed for hydroformed tubes with and without considering heat treatment effects. Also, finite element simulations were carried out for sequential procedures of bending and hydro-formi...
In order to improve the mechanical properties and simultaneously reduce the thermal expansion coefficient (CTE) of epoxy resins under low temperature, a study of the effect of a liquid-type additive, polydimethylsiloxane (PDMS) on the cryogenic properties was performed. Phenol novolac-based epoxy resin was blended with an aromatic amine curing agen...
Nano carbons reinforced aluminium (Al) alloy composites have been fabricated successfully by the surface treatment of nano carbons and the unique casting method, liquid pressing process. CNTs and CNFs have been coated with metal and/or oxide in order to improve the wettability between nano carbons and metallic melts. In liquid pressing process, Al...
In this work, reduced graphene oxide (rGO) paper has been fabricated using bio-inspired adhesive polydopamine (pDop). Dopamine mimics the catechol-amine structure in the mussel's adhesive foot protein, mytilus edulis. Also, dopamine can be utilized as an effective reducing agent due to its oxidative self-polymerization. Therefore, pDop embedded rGO...
A new water-soluble and self-doped poly(styrenesulfonic acid-graft-aniline), PSSA-g-PANI, for dispersing carbon nanotubes (CNTs) in water was synthesized and its ability to stabilize aqueous CNT dispersions was examined. It was observed that the PANI in PSSA-g-PANI, which has benzoid and quinoid structure, was strongly adsorbed onto the nanotube su...
Composites with multi-scale reinforcements consisting of multi-walled carbon nanotubes (MWCNTs) or carbon nanofibers (CNFs), along with micron-sized advanced carbon fibers, were processed using electro-phoretic deposition (EPD) technique. Both anodic and cathodic electrophoretic deposition processes have been utilized for the deposition of nanoscal...
An electrophoretic deposition process has been applied to produce unique carbon nanotube (CNT)/copper nanostructures on the
carbon fiber surfaces. During the deposition process, ionized copper and positively charged CNTs are accelerated towards the
carbon fiber under applied electric fields. An interconnected formicary-like network of nanotubes and...
Carbon nanotube reinforced copper (CNT/Cu) nanoplatelets were developed by a simple two-step deposition method; thermal vapor deposition of Cu and anodic eletrophoretic deposition of CNT. Due to the fast corrosion during the electrophoresis, the Cu layer is broken into pieces and exfoliated to form the platelet structures. Consequently, highly cond...
Springback behavior of automotive friction stir welded TWB (tailor welded blank) sheets was experimentally investigated and
the springback prediction capability of the constitutive law was numerically validated. Four automotive sheets, aluminum alloy
6111-T4, 5083-H18, 5083-O and dual-phase DP590 steel sheets, each having one or two different thick...
In order to maximize the performance of polymer nano-composites, it is essential to understand an effect of a dispersion state on material properties as well as to achieve highly dispersed composites. In this work, a simple quantitative approach to evaluate the degree of dispersion was suggested for carbon nanotube (CNT) embedded polymer nano-compo...
Due to the superior structural performance, fiber reinforced composites have been paid attention as the candidate materials for cryogenic storage tanks in the aerospace and LNG transport applications. Therefore thermal expansion properties of composite materials should be well characterized at the cryogenic environment and precise numerical approac...
Cu/carbon nano-particle hybrids were fabricated through the cathodic electrophoretic deposition (EPD) process. CNT and CNF nano-particles were modified to give positive charges by polyethyleneimine (PEI) treatment before depositing them on the substrate. Since a Cu plate was used as an anode in the EPD process, Cu particles were also deposited alon...
Three types of glass woven fabrics (plain, balanced twill, and unbalanced twill) having various sample sizes and aspect ratios were tested using the bias-extension tests. Real-time deformation images, force, and displacement data were collected. For the bias-extension test, the shear angle of the fabrics from the equation based on the crosshead dis...
Through the international corporative benchmark works, the material characterization of the woven fabric composites has been
examined to better understand their mechanical properties and to provide the process design information for numerical analysis.
As the second stage of the benchmark work, the double-dome geometry has been used to illustrate t...
Since the fiber reinforced polymeric (FRP) composites are considered in next generation of space transportation systems, reliable thermal expansion properties should be well provided for structural design of composite materials. To obtain accurate mechanical behaviors at a cryogenic temperature, precise strain measurement and calibration must be pr...
In order to increase the electrical conductivity and the mechanical properties of carbon fabric composites, multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) were deposited on carbon fabrics by anodic and cathodic electrophoretic deposition (EPD) processes. In the cathodic EPD, carbon nano-particles and nano-sized Cu particles wer...
One of the biggest challenges in the nano-field is how to effectively disperse nano-scale particles, especially CNTs, which are strongly agglomerated by intermolecular van der Waals forces. This study suggests a new method, discharge flocking, in order to disperse nano-scale particles effectively, which combines corona discharge phenomenon and a tr...
Tensile and flexural properties and electrical conductivity of MWCNT/epoxy composites with different aspect ratios of MWCNTs were compared. The MWCNT/epoxy mixtures were prepared by mechanical dispersion methods using a homomixer and a three-roll mill, and then composite samples were fabricated by compression molding process. The fractured surfaces...
One of the big challenges in the nano-field is how to effectively disperse nanoscale
particles, especially CNTs and carbon blacks, which are strongly
agglomerated by intermolecular van der Waals forces. Solution-based dispersion
methods such as sonication and three-roll milling require lots of dispersion time
and have re-agglomeration problems afte...
Formability of automotive friction stir welded TWB (tailor-welded blank) sheets was experimentally and numerically investigated in this work for four automotive sheets, aluminum alloy 6111-T4, 5083-H18, 5083-O and DP590 steel sheets, each having one or two different thicknesses. In particular, formability in three applications including the simple...
In order to evaluate the macroscopic performance of friction stir welded automotive tailor-welded blank (TWB) sheets, the hardening behavior, anisotropic yielding properties and forming limit diagram were characterized both for base (material) and weld zones. In order to describe the Bauschinger and transient hardening behaviors as well as permanen...
In order to evaluate the formability of friction stir welded (FSW) automotive TWB (tailor-welded blank) sheets with respect to base material direction, the aluminum alloy 6111-T4 sheet was joined with three different types of combination: RD||RD, TD||RD, TD||TD (Here, RD and TD mean the rolling direction and transverse direction, respectively). For...
The subtle distortions after flanging operations on outer automotive panels are highly undesirable on class-1 finish panels. Since existing finite element software do not have the ability to accurately predict or capture these subtle distortions, die designers rely on expensive and time-consuming physical tryouts to verify and adjust their design....
In order to improve the structural and functional properties of nano-particles reinforced polymer composites, an approach to evaluate a degree of dispersion of the carbon nano-particles was developed. A transmittance of CNTs reinforced composites was measured by UV-visible spectroscopy. The effect of the number of dispersion process cycles at a dif...
Finite element simulations were performed for the sequential procedures of bending and hydro-forming of DP590 tubes in order to optimize the process parameters, in particular, the boost condition and axial feeding in the sequential forming processes considering formability and spring-back. The effects of the material property, including strain-rate...
In order to investigate formability performance and also to obtain guidelines for the stamping process design of friction stir welded TWB (tailor welded blank) sheets, the hemispherical dome stretching test was experimentally performed and the results of the base and friction stir welded samples were compared. Also, in order to better understand th...
The double-dome geometry, proposed as a benchmark in earlier ESAFORM conferences, will be used in this paper to illustrate
the effect of material models on the forming behaviors of the woven composites parts. Numerical simulations of forming of
woven composites can be mainly classified into two categories, kinematic based and continuum-mechanics ba...
To prevent a sheet specimen from buckling subjected to a tension-compression cyclic loading, a new fixture has been developed to use with a regular tensile-compression machine. The novelty of this device lies in 4-block wedge design with pre-loaded springs. This design allows blocks to freely move in the vertical direction while providing the norma...
In this work, the mechanical properties of the metal active gas (MAG) weld zone and heat affected zone (HAZ) were characterized utilizing the continuous indentation method together with its finite element (FEM) analysis. To verify the measured properties, uni-axial tension and three point bending tests were performed for DP590 welded specimens. For...
Since the thermoforming technology for composite materials can lead the manufacturing cost and time to be significantly reduced, it has been widely adopted for the large-scaled mass production of composite applications. In order to find the optimum forming process parameters, the accurate material constitutive model should be incorporated through i...
In order to investigate the formability of friction stir welded(FSW) tailor welded blanks(TWB) with respect to the base material`s directional combination, aluminum alloy AA6111-T4 sheets were welded with three different conjoining types: RD-RD, TD-RD and TD-TD. Here, RD and TD represent rolling and transverse directions, respectively. For experime...
The constitutive law to describe the anisotropic and asymmetric mechanical behavior of AZ31B magnesium (Mg) alloy sheets at room temperature has been developed here for the plane stress condition, based on the orthotropic yield criterion proposed by Cazacu O, Plunkett B, Barlat F. [Orthotropic yield criterion for hexagonal closed packed metals. Int...
Textile composites made of woven fabrics have demonstrated excellent mechanical properties for the production of high specific-strength products. Research efforts in the woven fabric sheet forming are currently at a point where benchmarking will lead to major advances in understanding both the strengths and the limitations of existing experimental...
Woven-fabric reinforced composites have gained a significant attention from both industrial and academic fields, due to their high specific strength and stiffness as well as their supreme formability characteristics. In this work, the challenges in woven composites forming, from material variations, experimental material characterization methods to...
The shear behavior of woven fabric composites in the past has been mainly assumed to be independent on the tensions in yarns
and therefore, the tension-shear behavior can be decoupled in the constitutive model. Recent experimental results showed that
the in-plane tension can affect the shear force. In this work, the non-orthogonal constitutive mode...
In order to numerically evaluate hydro-formed DP-steel tubes on crash performance considering welding heat effects, finite element simulations of crash behavior were performed for hydro-formed tubes with and without heat treatment effects. Also, finite element simulations were performed for the sequential procedures of bending and hydro-forming of...
Characterization of material hardening behavior has been investigated by many researchers in the past decades. Experimental investigation of thin sheet metals under cyclic loading has become a challenging issue. A new test fixture has been developed to use with a regular tensile-compression machine (for example, MTS machine). Experimental results o...
As a result of international corporative benchmark works, material characterization of the woven fabric reinforced composites has been examined to better understand their mechanical properties and to provide the process design information for numerical analysis. Here, in order to predict thermo‐forming behaviors of woven composites, the double dome...
