• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.401-401
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• 2014

In this study, graphene, the most attractive material today, has been applied to the wavelength-modulated surface plasmon resonance (SPR) sensor. The optical fiber sensor technology is the most fascinating topic because of its several benefits. In addition to this, the SPR phenomenon enables the detection of biomaterials to be label-free, highly sensitive, and accurate. Therefore, the optical fiber SPR sensor has powerful advantages to detect biomaterials. Meanwhile, Graphene shows superior mechanical, electrical, and optical characteristics, so that it has tremendous potential to be applied to any applications. Especially, grapheme has tighter confinement plasmon and relatively long propagation distances, so that it can enhance the light-matter interactions (F. H. L. Koppens, et al., Nano Lett., 2011). Accordingly, we coated graphene on the optical fiber probe which we fabricated to compose the wavelength-modulated SPR sensor (Figure 1.). The graphene film was synthesized via thermal chemical vapor deposition (CVD) process. Synthesized graphene was transferred on the core exposed region of fiber optic by lift-off method. Detected analytes were biotinylated double cross-over DNA structure (DXB) and Streptavidin (SA) as the ligand-receptor binding model. The preliminary results showed the SPR signal shifts for the DXB and SA binding rather than the concentration change.

• Composites Research
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• v.28 no.5
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• pp.265-269
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• 2015

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-functionalized graphene fibers by simple wet-spinning of diamine-functionalized graphene oxide (GO-$NH_2$), which is used because of its synthetic convenience, good dispersity, and scalable production with low cost. The amine-functionalized graphene fiber shows high electrical and mechanical properties compared to pristine graphene oxide fiber due to the electrostatic interaction between amine groups and electronegative functional groups of graphene oxide.

• Structural Engineering and Mechanics
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• v.87 no.4
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• pp.375-389
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• 2023

In many fiber concrete beams with Carbon Fiber Reinforced Polymer (CFRP), debonding occurs between the carbon sheets and the concrete due to the low strength of the bonding resin. A total of 42 fiber concrete beams with a cross-section of 10×10 cm with a span length of 50 cm are fabricated and retrofitted with CFRP and subjected to a 4-point bending test. Graphene Oxide (GO) at 1, 2, and 3 wt% of the resin is used to improve the mechanical properties of the bonding resins, and the effect of length, width, and the number of layers of CFRP and resin material are investigated. The crack pattern, failure mode, and stress-strain curve are analyzed and compared in each case. The results showed that adding GO to polyamine resin could improve the bonding between the resin and the fiber concrete beam. Furthermore, the optimum amount of nanomaterials is equal to 2% by the weight of the resin. Using 2% nanomaterials showed that by increasing the length, width, and number of layers, the bearing and stiffness of fiber concrete beams increased significantly.

• Carbon letters
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• v.23
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• pp.17-21
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• 2017

Polyurethane (PU) nanofibers containing graphene oxide (GO) and Ag doped functionalized reduced graphene oxide (Ag-RGO) were successfully prepared via the electrospinning technique. The uniform distribution of GO sheets along with Ag nanoparticle in the nanofibers was investigated by scanning electron microscopy and the elemental mapping technique. X-ray diffraction and thermal gravimetric analysis verified the presence of GO and Ag in the bicomposite nanofibrous mats. Antibacterial tests against Escherichia coli demonstrated that the addition of GO and Ag-RGO to the PU nanofiber greatly enhanced bactericidal efficiency. Overall, these features of the synthesized nanofibers make them a promising candidate material in the biomedical field for applications such as tissue engineering, wound healing, and drug delivery systems.

• Bulletin of the Korean Chemical Society
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• v.35 no.4
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• pp.1011-1015
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• 2014

Octadecyl-modified graphene (graphene-C18) was fabricated and used as adsorbent in hollow fiber liquid phase microextraction (HF-LPME) for the first time. The extraction performance of graphene-C18 reinforced HF-LPME was evaluated using chlorophenols as model analytes. The factors affecting the extraction efficiency, such as extraction time, pH of the sample solution, agitation rate, the concentration of graphene-C18 and salt addition were optimized. After the graphene-C18 reinforced HF-LPME of the chlorophenols from honey sample, the analytes were separated and determined by high-performance liquid chromatography. The linearity was observed in the range of 5.0-200.0 ng $g^{-1}$ for 2-chlorophenol and 3-chlorophenol, and 2.0-200.0 ng $g^{-1}$ for 2,3-dichlorophenol and 3,4-dichlorophenol, respectively. The limits of detection (S/N = 3) of the method were lower than 1.5 ng $g^{-1}$. The recoveries of the method were between 88% and 108%. The method is simple, sensitive and has been resoundingly applied to analysis of chlorophenols in honey samples.

• Composites Research
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• v.30 no.5
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• pp.316-322
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• 2017

Carbon fiber is a material with excellent mechanical, electrical and thermal properties, which is widely used as a composite material made of a polymer matrix. However, this composite material has a weak point of interlaminar delamination due to weak interfacial bond with polymer matrix compared with high strength and elasticity of carbon fiber. In order to solve this problem, it is essential to use reinforcements. Due to excellent mechanical properties, graphene have been expected to have large improvement in physical properties as a reinforcing material. However, the aggregation of graphene and the weak interfacial bonding have resulted in failure to properly implement reinforcement effect. In order to solve this problems, dispersibility will be improved. In this study, functionalization of graphene nanoplatelet was proceeded with melamine and mixed with epoxy polymer matrix. The carbon fiber reinforced polymer composites were fabricated using the prepared graphene nanoplatelet/epoxy and flexural properties and interlaminar shear strength were measured. As a result, it was confirmed that the dispersibility of graphene nanoplatelet was improved and the mechanical properties of the composite material were increased.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.408-408
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• 2014

Graphene has received attention with its high electron mobility and visual transparency as a promising material for optoelectronic and photonic applications. Combination of graphene and conducting nanostructures i.e. plasmonic structures has recently been researched for enhancing light-matter interaction and overcoming diffraction limit of light. Here we show enhanced photodetection of incoherent visible light with graphene-mediated plasmonics. Gold nanoparticles fabricated by focused ion beam was used as an active element of photodetection and graphene was utilized as an interfacing material between nanostructures and electrodes. Hot electrons generated upon plasmon decay within nanoparticles pass over the potential barrier between nanostructure and graphene and give rise to a photocurrent with built-in electric field. We report 76.7% enhancement of photocurrent under resonant irradiation of fiber-coupled halogen lamp compared to the case without light illumination. We showed wavelength-dependent current response arisen from plasmonic nanostructure, providing a good agreement with theoretical calculation.

• Steel and Composite Structures
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• v.44 no.5
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• pp.707-720
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• 2022

In the present work, bending and free vibration analyses of multilayered functionally graded (FG) graphene platelet (GPL) and fiber-reinforced hybrid composite beams are carried out using the parabolic function based shear deformation theory. Parabolic variation of transverse shear stress across the thickness of beam and transverse shear stress-free conditions at top and bottom surfaces of the beam are considered, and the proposed formulation incorporates a transverse displacement field. The present theory works only with four unknowns and is computationally efficient. Hamilton's principle has been employed for deriving the governing equations. Analytical solutions are obtained for both the bending and free vibration problems in the present work considering different variations of GPLs and fibers distribution, namely, FG-X, FG-U, FG-Λ, and FG-O for beams having simply-supported boundary condition. First, the matrix is assumed to be strengthened using GPLs, and then the fibers are embedded. Multiscale modeling for material properties of functionally graded graphene platelet/fiber hybrid composites (FG-GPL/FHRC) is performed using Halpin-Tsai micromechanical model. The study reveals that the distributions of GPLs and fibers have significant impacts on the stresses, deflections, and natural frequencies of the beam. The number of layers and shape factors widely affect the behavior of FG-GPL-FHRC beams. The multilayered FG-GPL-FHRC beams turn out to be a good approximation to the FG beams without exhibiting the stress-channeling effects.

• Carbon letters
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• v.15 no.1
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• pp.67-70
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• 2014

In this work, nanocomposites of epoxy resin and chemically reduced graphene oxide (RGO) were prepared by thermal curing process. X-ray diffractions confirmed the microstructural properties of RGO. Differential scanning calorimetry was used to evaluate the curing behaviors of RGO/epoxy nanocomposites with different RGO loading amounts. We investigated the effect of RGO loading amounts on the mechanical properties of the epoxy nanocomposites. It was found that the presence of RGO improved both flexural strength and modulus of the epoxy nanocomposites till the RGO loading reached 0.4 wt%, and then decreased. The optimum loading achieved about 24.5 and 25.7% improvements, respectively, compared to the neat-epoxy composites. The observed mechanical reinforcement might be an enhancement of mechanical interlocking between the epoxy matrix and RGO due to the unique planar structures.

• Composites Research
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• v.24 no.4
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• pp.1-4
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• 2011

In this work, we successfully fabricated graphene oxide (GO) and GO-based PMMA composite fiber and nylon films. Dynamic mechanical and tensile properties of PMMA-GO composite fiber showed that GO is efficient reinforcement for polymer matrices. However, Nylon 6,6-GO composite films showed low reinforcement efficiency in terms of dynamic mechanical and tensile properties due to the colloid instability of GO in formic acid at a low pH level.