• Carbon letters
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• v.11 no.4
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• pp.279-284
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• 2010

Graphene is one of the most promising materials for many applications. It can be used in a variety of applications not only as a reinforcement material for polymer to obtain a combination of desirable mechanical, electrical, thermal, and barrier properties in the resulting nanocomposite but also as a component in energy storage, fuel cells, solar cells, sensors, and batteries. Recent research at Michigan State University has shown that it is possible to exfoliate natural graphite into graphite nanoplatelets composed entirely of stacks of graphene. The size of the platelets can be controlled from less than 10 nm in thickness and diameters of any size from sub-micron to 15 microns or greater. In this study we have investigated the influence of melt compounding processing on the physical properties of a polyamide 6 (PA6) nanocomposite reinforced with exfoliated graphite nanoplatelets (xGnP). The morphology, electrical conductivity, and mechanical properties of xGnP-PA6 nanocomposite were characterized with electrical microscopy, X-ray diffraction, AC impedance, and mechanical properties. It was found that counter rotation (CNR) twins crew processed xGnP/PA6 nanocomposite had similar mechanical properties with co-rotation (CoR) twin screw processed or with CoR conducted with a screw design modified for nanoparticles (MCoR). Microscopy showed that the CNR processed nanocomposite had better xGnP dispersion than the (CoR) twin screw processed and modified screw (MCoR) processed ones. It was also found that the CNR processed nanocomposite at a given xGnP content showed the lowest graphite X-ray diffraction peak at $26.5^{\circ}$ indicating better xGnP dispersion in the nanocomposite. In addition, it was also found that the electrical conductivity of the CNR processed 12 wt.% xGnP-PA6 nanocomposite is more than ten times higher than the CoR and MCoR processed ones. These results indicate that better dispersion of an xGnP-PA6 nanocomposite is attainable in CNR twins crew processing than conventional CoR processing.

• Journal of the Korean GEO-environmental Society
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• v.15 no.6
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• pp.67-73
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• 2014

Landslide disasters including debris flows are the one of the most frequent natural disasters in Korea, and losses of lives and property damages due to these catastrophic events have been increased every year. Various mitigation programs and related policies have been conducted in order to respond and prepare landslide disasters. Most landslide reduction programs are, however, focused on recovery actions after the disasters and lead to unrealistic consequences to the affected people and their properties. The main objective of this study, therefore, is to evaluate the landslide hazard based on the identification of geomorphological features, which is for the preparedness of the landslide disasters. Two methodologies, SINMAP and vector dispersion analyses are used to simulate those characteristics where landslides are actually located. Results showed that both methods well discriminate geomorphic features between stable and unstable domains. This proves that geomorphological characteristics well describe a relationship with the existing landslide hazard. SINMAP analysis which is based on the consecutive model considering external factors like infiltration is well identify the landslide hazard especially for debris flow type landslides rather than vector dispersion focusing on a specific area. Combining with other methods focusing specific characteristics of geomorphological feature, accurate landslide hazard assessments are implemented.

• Journal of Adhesion and Interface
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• v.9 no.1
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• pp.3-8
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• 2008

Self-sensing was evaluated for carbon nanofiber (CNF)/epoxy composites with two different aspect ratios via electro-micromechanical technique and wettability test. Volumetric electrical resistance was measured to evaluate the comparative dispersion degree indirectly and it decreased due to the increase of electric contacts with increasing CNF concentration. The dispersion degree was evaluated indirectly by calculating coefficient of variation (COV) of volumetric electrical resistance. The CNF type A with a high aspect ratio showed better self-sensing than the case of CNF type B with a short aspect ratio. The CNF type B/epoxy composite showed little self-sensing at a concentration higher than 2 vol% probably due to poor dispersion. The apparent modulus of CNF type B was higher than that of CNF type A due to the orientation effect and the high surface area. The thermodynamic work of adhesion was consistent with the result of apparent modulus.

• Applied Chemistry for Engineering
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• v.26 no.1
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• pp.23-28
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• 2015

Lacquer sap extracted from lacquer trees exhibits good thermal stabilities and antimicrobial properties. To apply these superior properties to functional packaging, polyurushiol (YPUOH) powders were prepared and blended into LDPE (low density polyethylene) to prepare three different LDPE/YPUOH composite films via a twin screw extruder system. Their morphology, thermal and antimicrobial properties as well as barrier properties of the LDPE/YPUOH composite films were thoroughly investigated to find out applicablities of the films as functional packaging materials. Although the interfacial interaction between LDPE and YPUOH was relatively weak, LDPE/YPUOH composite films exhibited good dispersion of YPUOH in LDPE, resulting in the enhanced thermal stability with YPUOH loading. Due to the good antibacterial property of as-prepared YPUOH, LDPE/YUOH composite films also showed an excellent antibacterial activity (R) of 99.9% against E. coli. Furthermore, the moisture barrier property of LDPE/YPUOH composite films increased with increasing YPUOH contents. Incorporating the relatively low amount of YPUOH in LDPE resulted in the apparent enhancement in thermal stabilities, antibacterial and moisture barrier properties, which made them promising candidates as a functional filler for packaging materials.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.173-173
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• 2010

$Bi_4Ti_3O_{12}$ ($B_4T_3$) is a unique ferroelectric material that has a relatively high dielectric constant, high Curie temperature, high breakdown strength, and large spontaneous polarization. As a result this material has been widely studied for many applications, including nonvolatile ferroelectric random memories, microelectronic mechanical systems, and nonlinear-optical devices. Several reports have appeared on the use of Mn dopants to improve the electrical properties of $B_4T_3$ thin films. Mn ions have frequently been used for this purpose in thin films and multilayer capacitors in situations where intrinsic oxygen vacancies are the major defects. However, no systematic study of the optical properties of $B_4T_3$ films has appeared to date. Here, we report optical data for these films, determined by spectroscopic ellipsometry (SE). We also report the effects of thermal annealing and Mn doping on the optical properties. The SE data were analyzed using a multilayer model that is consistent with the original sample structure, specifically surface roughness/$B_4T_3$ film/Pt/Ti/$SiO_2$/c-Si). The data are well described by the Tauc-Lorentz dispersion function, which can therefore be used to model the optical properties of these materials. Parameters for reconstructing the dielectric functions of these films are also reported. The SE data show that thermal annealing crystallizes $B_4T_3$ films, as confirmed by the appearance of $B_4T_3$ peaks in X-ray diffraction patterns. The bandgap of $B_4T_3$ red-shifts with increasing Mn concentration. We interpret this as evidence of the existence deep levels generated by the Mn transition-metal d states. These results will be useful in a number of contexts, including more detailed studies of the optical properties of these materials for engineering high-speed devices.

• Composites Research
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• v.36 no.4
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• pp.246-252
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• 2023

A secondary barrier made of glass fiber reinforced composites has been installed infinitely using automatic bonding machine(ABM) in membrane type LNG cargo containment system (CCS). At the same time, significant thermal stress due to cryogenic heat shrinkage has occurred in the composite on the non-bonding area between the adhesive fixation at both ends. There have been studies from the perspective of structural safety evaluation taking this into account, but none that have analyzed mechanical property taking an prolonged length into account. In this study, 2-parameter Weibull distribution statistical analysis was used to standardize reliable mechanical property for actual length, taking into account the composite's brittle fracture of ceramic material with wide fracture strength dispersion. Related experimental data were obtained by performing uniaxial tensile tests at specific temperatures below cryogenic condition considering LNG environment. As a result, the mechanical strength increased about 1.5 times compared to -20℃ at -70℃ and initial non-linear behavior of fiber stretched was suppressed. As the temperature decreased until the cryogenic, the mechanical strength continued to increase due to cold brittleness. The suggested mechanical property in this study would be employed to secure reliable analysis support material property when assessing the safety of secondary barrier's structures.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.2
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• pp.1-8
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• 2018

In the soldering industry, a variety of lead-free solders have been developed as a part of restricting lead in electronic packaging. Sn-Ag-Cu (SAC) lead-free solder is regarded as one of the most superior candidates, owing to its low melting point and high solderability as well as the mechanical property. On the other hand, the mechanical property of SAC solder is directly influenced by intermetallic compounds (IMCs) in the solder joint. Although IMCs in SAC solder play an important role in bonding solder joints and impart strength to the surrounding solder matrix, a large amount of IMCs may cause poor strength, due to their brittle nature. In other words, the mechanical properties of SAC solder are of some concern because of the formation of large and brittle IMCs. As the IMCs grow, they may cause poor device performance, resulting in the failure of the electronic device. Therefore, new solder technologies which can control the IMC growth are necessary to address these issues satisfactorily. There are an advanced nanotechnology for microstructural refinement that lead to improve mechanical properties of solder alloys with nanoparticle additions, which are defined as nano-reinforced solders. These nano-reinforced solders increase the mechanical strength of the solder due to the dispersion hardening as well as solderability of the solder. This paper introduces the nano-reinforced solders, including its principles, types, and various properties.

• Polymer(Korea)
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• v.28 no.6
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• pp.551-555
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• 2004

Cellulose diacetate (CDA) nanocomposite films were prepared by using various plasticizer and montmorillonite nanofiller in methylene chloride/ethanol (9:1 w/w) mixed solution. The thermal property (T$_{g}$) of prepared CDA films was observed by DSC and T$_{g}$ of the films was decreased with the increase in the plasticizer content. The degree of dispersion of MMT in the CDA film was observed by XRD and mechanical property of CDA film was measured by tensile strength and Young's modulus. When the plasticizer was added into the CDA film upto 30 wt%, the Young's modulus of film was decreased from 1930 MPa to 1131 MPa but was increased from 1731 MPa to 2272 MPa when the MMT was added into the film upto 7 wt%. The mechanical properties of CDA films were decreased by addition of plasticizer but strengthened by the incorporation of MMT.

• Polymer(Korea)
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• v.35 no.2
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• pp.171-175
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• 2011

Isophorone diisocyanate(IPDI), polytetramethylene glycol 1000 (PTMG1000), and N-methyl diethanol amine (MDEA) were applied to prepare cationic polyurethane water dispersions (PUD). Various neutralizers and chain extenders were introduced in order to investigate property changes, such as particle size, viscosity, $T_g$, tensile strength, and water swellability, depending on chemical structure of those chemicals. While the PUDs neutralized by acetic acid showed a typical elastomeric behavior, the others used with hydrochloride presented crystalline behavior. Among chain extenders isophorone diamine (IPDA) provided the best mechanical property. The particle size of the PUD neutralized with HCl was smaller than that with acetic acid. It is believed that this is attributed to the size difference of counter ions. The PUD chain-extended with hydrazine had the smallest particle size.

• Polymer(Korea)
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• v.27 no.6
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• pp.576-582
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• 2003

When the halogenated flame retardant, decabromodiphenyl oxide, was added to the polypropylene/nylon blend, and was compounded with montmorillonite and compatibilizer, maleic anhydride polypropylene, the improvement of flame retardancy and mechanical properties was investigated. The degree of dispersion between polymer resin and inorganic nanoparticles was investigated, and the flame retardancy and mechanical properties was measured quantitatively. XRD results showed that the montrnorillonite was com-pletely exfoliated after polypropylen/nylon nanocomposites was mixed above twice. By compounding with montmorillonite, polypropylene/nylon blend system was overcome the deterioration of flame retardancy. The tensile strength and impact strength were slightly increased, and by compounding with montmorillonite, the additional increase in mechanical properties was obtained. Therefore, the flame retardancy of polypropylene / nylon blend was decreased by adding nylon, but by compounding with inorganic nanoparticle, improvement of the flame retardancy and mechanical properties was obtained.