• Journal of Korean Society of Disaster and Security
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• v.16 no.1
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• pp.91-103
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• 2023

This study aims to investigate the dynamic fracture characteristics of rocks and rock-like materials subjected to the Nonex Rock Cracker (NRC), a vapor pressure crushing agent that produces vapor pressure by instantaneously vaporizing a liquid mixture crystallized through the thermite reaction. Furthermore, the study seeks to develop an analytical technique for predicting the fracture pattern. A dynamic fracture test was performed on a PMMA block, an artificial brittle material, using the NRC. High-speed cameras and dynamic pressure gauges were employed to capture the moment of vapor pressure generation and measure the vapor pressure-time history, respectively. The 2-dimensional Dynamic Fracture Process Analysis (2D DFPA) was used to simulate the fracture process caused by the vapor pressure, with the applied pressure determined based on the vapor pressure-time history. The proposed analytical method was used to examine various fracture patterns with respect to granite material and high-performance explosives.

• Clean Technology
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• v.15 no.2
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• pp.102-108
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• 2009

In this study, poly(lactic acid) (PLA) was modified by reactive extrusion with a functional monomer GMA(glycidyl methacrylate), MMT(montmorillonite), and initiator to enhance the melt strength. Each modified PLA was prepared with different amounts of GMA and MMT and was characterized by measuring thennal- and melt-viscoelastic properties. The degree of dispersion of MMT was measured by X-ray diffraction(XRD) and transmission electron microscopy(TEM). The glass transition temperature($T_g$) of modified PLA-GMA-MMT nanocomposite decreased with increasing GMA content, but was a little affected by the amount of MMT. Surface analysis showed that the nanocomposite became more intercalated than exfoliated as the amount of MMT increases. The complex viscosity and storage modulus of the nano-composite were greatly increased by addition of MMT.

• Korean Journal of Materials Research
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• v.32 no.12
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• pp.522-527
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• 2022

Among efforts to improve techniques for the chemical vapor deposition of large-area and high-quality graphene films on transition metal substrates, being able to reliably transfer these atomistic membranes onto the desired substrate is a critical step for various practical uses, such as graphene-based electronic and photonic devices. However, the most used approach, the wet etching transfer process based on the complete etching of metal substrates, remains a great challenge. This is mainly due to the inevitable damage to the graphene, unintentional contamination of the graphene layer, and increased production cost and time. Here, we report the systematic study of an H₂ bubbling-assisted transfer technique for graphene films grown on Cu foils, which is nondestructive not only to the graphene film but also to the Cu substrate. Also, we demonstrate the origin of the graphene film tearing phenomenon induced by this H₂ bubbling-assisted transfer process. This study reveals that inherent features are produced by rolling Cu foil, which cause a saw-like corrugation in the poly(methyl methacrylate) (PMMA)/graphene stack when it is transferred onto the target substrate after the Cu foil is dissolved. During the PMMA removal stage, the graphene tearing mainly appears at the apexes of the corrugated PMMA/graphene stack, due to weak adhesion to the target substrate. To address this, we have developed a modified heat-press-assisted transfer technique that has much better control of both tearing and the formation of residues in the transferred graphene films.

• Journal of dental hygiene science
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• v.23 no.4
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• pp.264-270
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• 2023

Background: Resin-based dental materials release residual monomers or other substances from incomplete polymerization into the oral cavity, thereby causing adverse biological effects on oral tissue. 10-Methacryloyloxydecyl dihydrogen phosphate (10-MDP), an acidic monomer containing dihydrogen phosphate and methacrylate groups, is the most commonly used component of resin-based dental materials, such as restorative composite resins, dentin adhesives, and resin cements. Although previous studies have reported the cytotoxicity and biocompatibility in various cultured cells, the effects of resin monomers on cellular aging have not been reported to date. Therefore, this study aimed to investigate the effects of the resin monomer 10-MDP on cellular senescence and inflamm-aging in vitro. Methods: After stimulation with 10-MDP, MC3T3-E1 osteoblast-like cells were examined for cell viability by WST-8 assay and reactive oxygen species (ROS) production by flow cytometry. The protein and mRNA levels of molecular markers of aging were determined by western blotting and RT-PCR analysis, respectively. Results: Treatment with 0.05 to 1 mM 10-MDP for 24 hours reduced the survival of MC3T3-E1 cells in a concentration-dependent manner. The intracellular ROS levels in the 10-MDP-treated experimental group were significantly higher than those in the control group. 10-MDP at a concentration of 0.1 mM increased p53, p16, and p21 protein levels. Additionally, an aging pattern was observed with blue staining due to intracellular senescence-associated beta-galactosidase activity. Treatment with 10-MDP increased the levels of tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and IL-8, however their expression was decreased by mitogen-activated-protein-kinase (MAPK) inhibitors. Conclusion: Taken together, these results suggest that the exposure of osteoblast-like cells to the dental resin monomer 10-MDP, increases the level of cellular senescence and the inflammatory response is mediated by the MAPK pathway.

• Current Optics and Photonics
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• v.7 no.6
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• pp.721-731
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• 2023

This paper studies various roughness parameters, besides waviness, texture, and nonlinear parameters of Bismarck brown Y (BBY)-doped Poly(methyl methacrylate) (PMMA) films based on the computed values of optical limiting (OL) threshold power and nonlinear refractive index. The films' morphology, grain size, and absorption spectra were investigated using atomic force microscopy in conjunction with ultraviolet-visible (UV-Vis) spectrophotometer. The particle size of the films ranged between 4.11-4.51 mm and polymer films showed good homogeneity and medium roughness, ranging from 1.11-4.58 mm. A polymer film's third-order nonlinear optical features were carried out using the Z-scan methodology. The measurements were obtained by a continuous wave produced from a solid-state laser with a 532 nm wavelength. According to the results, BBY has a nonlinear refractive index of 10^-6 cm²/W that is significantly negative and nonlinear. The optical limiting thresholds are roughly 10.29, 13.52, and 18.71 mW, respectively. The shift of nonlinear optical features with the film's concentration was found throughout the experiment Additionally, we found that the polymer samples have outstanding capabilities for restricting the amount of optical power that may be transmitted through them. We propose that these films have the potential to be used in a wide variety of optoelectronic applications, including optical photodetectors and optical switching.

• Applied Chemistry for Engineering
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• v.35 no.3
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• pp.260-265
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• 2024

To synthesize an antistatic material for use in semiconductor wafer transport trays, in-situ polymerization of poly(methyl methacrylate) (PMMA) and polyurethane (PU) incorporating carbon nanotubes was designed and conducted. The newly synthesized composites were evaluated for their thermal and electrical conductivity properties under conditions mimicking commercial device manufacturing processes. Comparative analysis of their respective performances revealed that both PMMA and PU containing carbon nanotubes exhibited enhanced thermal properties and superior electrical conductivity as the nanotube content increased. Morphology of the composites synthesized via in-situ polymerization was confirmed to be excellent through FE-SEM analysis, demonstrating good dispersibility. Both PMMA and PU incorporating carbon nanotubes showed outstanding surface resistance values of 10³ Ω/□, indicating their suitability as antistatic materials for semiconductor applications.

• Korean Journal of Materials Research
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• v.34 no.9
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• pp.439-447
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• 2024

Organic-inorganic hybrid coating films have been used to increase the transmittance and enhance the physical properties of plastic substrates. Sol-gel organic-inorganic thin films were fabricated on polymethylmethacrylate (PMMA) substrates using a dip coater. Metal alkoxide precursor tetraethylsilicate (TEOS) and alkoxy silanes including decyltrimethoxysilane (DTMS), 3-glycidoxypropyltrimethoxysilane (GPTMS), phenyltrimethoxysilane (PTMS), 3-(trimethoxysilyl)propyl methacrylate (TMSPM) and vinyltrimethoxysilane (VTMS) were used to synthesize sol-gel hybrid coating solutions. Sol-gel synthesis was confirmed by the results of FT-IR. Cross-linking of the Si-O-Si network during synthesis of the sol-gel reaction was confirmed. The effects of each alkoxy silane on the coating film properties were investigated. All of the organic-inorganic hybrid coatings showed improved transmittance of over 90 %. The surface hardness of all coating films on the PMMA substrate was measured to be 4H or higher and the average thickness of the coating films was measured to be about 500 nm. Notably, the TEOS/DTMS coating film showed excellent hydrophobic properties, of about 97°.

• Journal of the Korean Vacuum Society
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• v.18 no.2
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• pp.85-91
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• 2009

There has been a rapid progress for flexible polymer-based MEMS(Microelectromechanical Systems) technology. Polycarbonate (PC) and Poly Methyl Methacrylate (PMMA), so-called acrylic, have many advantages for optical, non-toxic and micro-device application. We studied dry etching of PC and PMMA as a function of % gas ratio in the $O_2/SF_6/CH_4$ temary plasma. A photoresist pattern was defined on the polymer samples with a mask using a conventional lithography. Plasma etching was done at 100 W RIE chuck power and 10 sccm total gas flow rate. The etch rates of PMMA were typically 2 times higher than those of PC in the whole experimental range. The result would be related to higher melting point of PC compared to that of PMMA. The highest etch rates of PMMA and PC were found in the $O_2/SF_6$ discharges among $O_2/SF_6$, $O_2/CH_4$ and $SF_6/CH_4$ and $O_2/SF_6/CH_4$ plasma composition (PC: ${\sim}350\;nm/min$ at 5 sccm $O_2/5$ sccm $SF_6$, PMMA: ${\sim}570\;nm/min$ at 2.5 sccm $O_2/7.5$ sccm $SF_6$). PC has smoother surface morphology than PMMA after etching in the $O_2/SF_6/CH_4$ discharges. The surface roughness of PC was in the range of 1.9$\sim$3.88 nm. However, that of PMMA was 17.3$\sim$26.1 nm.

• Journal of Food Hygiene and Safety
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• v.30 no.1
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• pp.81-86
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• 2015

The purpose of our paper was to investigate the migration level of 4,4'-MDA(4,4'-methylenedianiline), 2,4-TDA(2,4-toluenediamine), aniline, acrylonitrile and methylmeth acrylate from plastic cookwares into food simulants and to evaluate the safety of each monomers. The test articles for monomers were PA (polyamide) items for 4,4'-MDA, 2,4-TDA and aniline, PU (polyurethane) items for 4,4'-MDA, ABS (acrylonitrile-butadiene- styrene) items for acrylonitrile, and acrylic resin items for methylmethacrylate. All the article samples of 321 intended for contact with foods were purchased in domestic market. 4,4'-MDA, 2,4-TDA and aniline were analyzed by LC-MS/MS (liquid chromatography -tandem mass spectrometer), acrylonitrile by GC-NPD (gas chromatography-nitrogen phos phorus detector) and methyl methacrylate by GC-FID (gas chromatography-flame ionization detector). The migration level of monomers were within the migration limits of Ministry of Food and Drug Safety (MFDS). As a result of safety evaluation, our results showed that the estimated daily intake (EDI, mg/kg bw/day)s were $2.39{\times}10^{-9}$ and $1.20{\times}10^{-9}$ for 4,4'-MDA and 2,4-TDA of PA, $4.32{\times}10^{-9}$ for acrylonitrile of ABS and $2.27{\times}10^{-7}$ for methylmethacrylate of acrylic resin. Reference Dose (RfD, mg/kg bw/day) of acrylonitrile and tolerable daily intake (TDI, mg/kg bw/day) of methacrylate were established respectively as 0.001 by EPA (US Environmental Protection Agency) and as 1.2 by WHO (World Health Organization). When comparing with RfD and TDI, the EDIs of acrylonitrile and methylmethacrylate accounted for $4.32{\times}10^{-4}%$ and $1.89{\times}10^{-5}%$ respectively.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.2
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• pp.223-232
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• 2012

Purpose: Validating a new research method to determine posterior corneal curvature and asphericity(Q) in vivo, based on measurements of anterior corneal topography and corneal thickness. Methods: Anterior corneal topographic data, derived from the Medmont E300 corneal topographer, and total corneal thickness data measured along the horizontal corneal meridian using the Holden-Payor optical pachometer, were used to calculate the anterior and posterior corneal apical radii of curvature and Q. To calculate accurate total corneal thickness the local radius of anterior corneal curvature, and an exact solution for the relationship between real and apparent thickness were taken into consideration. This method differs from previous approach. An elliptical curve for anterior and posterior cornea were calculated by using best fit algorism of the anterior corneal topographic data and derived coordinates of the posterior cornea respectively. For validation of the calculations of the posterior corneal topography, ten polymethyl methacrylate (PMMA) lenses and right eyes of five adult subjects were examined. Results: The mean absolute accuracy (${\pm}$standard deviation(SD)) of calculated posterior apical radius and Q of ten PMMA lenses was $0.053{\pm}0.044mm$ (95% confidence interval (CI) -0.033 to 0.139), and $0.10{\pm}0.10$ (95% CI -0.10 to 0.31) respectively. The mean absolute repeatability coefficient (${\pm}SD$) of the calculated posterior apical radius and Q of five human eyes was $0.07{\pm}0.06mm$ (95% CI -0.05 to 0.19) and $0.09{\pm}0.07$ (95% CI -0.05 to 0.23), respectively. Conclusions: The result shows that acceptable accuracy in calculations of posterior apical radius and Q was achieved. This new method shows promise for application to the living human cornea.