Search

In this study, the effects of physicochemical treatments of illite on thermo-mechanical properties and thermal stability of the hybrid illite/epoxy composites were investigated. Illite was chemically modified with octadecylamine (ODA), to become more organophilic and also physically modified by wet ball-milling process, so that the illite dispersion in the epoxy matrix and interfacial adhesion between illite and epoxy resin could be improved. Then, as-received illite and physically and/or chemically modified illites were mixed with epoxy separately to produce hybrid illite/epoxy composites and their thermo-mechanical properties and thermal stability were investigated. Chemical modification was confirmed with FTIR and the aforementioned properties of illite/epoxy composites were characterized with SEM, DMA, and TGA. IR results show that ODA modification of illite was successful and thermo-mechanical properties were enhanced with illite introduction to the epoxy resin, especially when physically and chemically modified illite was added, showing about 100% increase in storage and loss modulus, compared to the pure epoxy. However, thermal stability was not enhanced by forming the illite/epoxy composites, because the composites prepared in this study were intercalated and flocculated illite/epoxy microcomposites.

In this study, a unique two-step process, i.e., an oxyfluorination-assisted graft polymerization (OAGP), was used to modify the surface properties of low-density polyethylene (LDPE) films. Based on the results of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) method, which was performed to estimate the amount of hydroperoxides generated by oxyfluorination, oxyfluorination conditions that maximize the amount of hydroperoxide groups were selected. Hydroperoxides were generated by oxyfluorination to provide active sites for the OAGP of the different monomers. Depending on the type of monomers used, two different graft polymerization behaviors were observed. Hydrophilic methacrylic acid (MA) monomers were graft polymerized onto the oxyfluorinated LDPE (OFPE) surface in a perpendicular direction, forming a spike-shaped morphology. On the other hand, hydrophobic styrene (ST) monomers were graft polymerized parallel to the OFPE surface, forming a valley-shaped morphology. By changing the type of vinyl monomers, two different surfaces could be prepared using the hydroperoxides generated by oxyfluorination. After OAGP with MA monomers, a hydrophilic surface following the Wenzel model was obtained, whereas after OAGP with ST monomers, a hydrophobic surface following the Cassie–Baxter model was obtained. Therefore, the OAGP process may be an efficient method for preparing two different surfaces by changing the monomer used.

To investigate new potential application of a clay material for C/C composites, illite added C/C composites were prepared with various illite contents. The improvement of filler effect by illite size reduction was also investigated using wet ballmilling by evaluating illite/phenolic resin infiltration using bulk density and porosity measurements, chemical structural changes of the composites using XRD, and thermal oxidation stability in air of the composites using TGA. The size reduction of illite resulted in narrower particle size distribution and improved illite infiltration into carbon preform. And the resultant C/ C composites prepared with illite had even more improved thermal oxidation stability in air, showing more increased IDTs up to 100oC, compared to those of the C/C composites with pristine illite, due to the SiC formation through carbothermal reduction between illite and carbon materials. The illite induced delay in oxidation of the illite-C/C composites was also observed and the delayed oxidation behavior was attributed to the layered structure of illite, which improved illite/phenol resin infiltration. Therefore, the potential use of illite as filler to improve oxidation stability of C/C composite can be promising. And the size reduction of illite can improve its effect on the desired properties of illite-C/C composites even more.

We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.

The role of the –N(CH2CH2OH)2 group in producing a mutagenic response from 4-((3-(2-hydroxyethoxy)4-amino)phenylazo)-N,N-bis(2-hydroxyethyl)aniline has been investigated. To accomplish this goal, a group of substituted 4,4′-diaminoazobenzene dyes was synthesized, and their structures were confirmed using 1H NMR, TOF-LC-ESI mass spectrometry, and combustion analysis. Mutagenicity was determined using the standard Ames test in Salmonella strains TA98, TA100, and TA1538 with and without S9 enzyme activation. The results of this study provide evidence that the mutagenicity of the parent dye arises from the metabolic cleavage of N-hydroxyethyl groups to give the corresponding –NHCH2CH2OH and –NH2 substituted monoazo dyes as direct-acting mutagens. All 5 of the dyes studied were mutagenic at various levels with and without S9 enzyme activation in TA1538. In addition, the results show that removing one N-hydroxyethyl group and capping both –OH groups in the parent dye did not affect mutagenicity, whereas removing both N-hydroxyethyl groups produced a strong direct-acting mutagen in all three bacterial strains. Increasing the length of the N-alkyl chain from two to three carbon atoms eliminated mutagenicity in TA98 without S9 activation.

The application of an electric field was found to markedly increase the sensitivity of a gas sensor system. Multi-walled carbon nanotubes (MWCNTs) were used as a gas-sensing material in order to detect a target nitrogen monoxide (NO) gas. The response of the gas sensor was evaluated under both positive and negative electric fields at various applied voltages. The responsiveness of the gas sensor increased by a factor of 2.5 as a function of increasing positive electric fields because of the optimized electron acceptor–donor reaction between the NO gas and the MWCNTs. It was concluded that the applied electric field accelerated the electron transfer between the NO gas and the MWCNTs.

Multi-walled carbon nanotubes were embedded into e-beam-cured epoxy resin to improve the mechanical properties of epoxy resin. The surfaces of these carbon nanotubes were modified using a fluorination treatment to improve their dispersion and adhesion in epoxy resin. The dynamic mechanical properties of epoxy/carbon nanotube composites were investigated at various heating rates and frequencies. As an effect of fluorination treatment, the semi-ionic bond of C–F on the surface of multi-walled carbon nanotubes played an important role in the improved dispersion and adhesion of carbon nanotubes into the epoxy resin. The storage modulus and loss modulus of the composites increased with higher applied frequency. The activation energy of the composites was increased by the effects of a higher heating rate due to the slow heat transfer in the epoxy/carbon nanotube composites. Eventually, the dynamic mechanical properties of the investigated epoxy were significantly improved by the carbon nanotubes dispersed therein via the fluorination treatment.

In this study, TiO2-Activated carbon (AC) complex fibers were prepared by electrospinning for the synergetic effect of adsorption and degradation of organic pollutant. The average diameter of these fibers increased with increasing the amount of AC added, except for 1AC-TOF (AC/TiO2 =1/40 mass ratio). After calcinations at 500oC, long as-spun fibers were broken and their average diameter was slightly decreased. The resultant fibers after calcination had rough surface and sphere shapes like a peanut. From XRD results, it was confirmed that as-spun fibers were changed to anatase TiO2 fiber after calcinations at 500oC. The prepared TiO2-AC complex fibers could remove procian blue dyes by solar light irradiation with high removal property of 94~99%. The PB dye was rapidly removed by adsorption during the initial 5 minutes. But after 5 minutes, dye removal was occurred by photodegradation. In this study, the most efficient AC/TiO2 ratio of TiO2-AC complex fibers was 5/ 40, showing the synergetic effect of adsorption and photodegradation. It is expected that the TiO2-AC complex fibers can be used to remove of organic pollutants in water system.

In this study, porous electrospun carbon fibers were prepared by electrospinning with PAN and , as a MgO precursor. MgO was selected as a substrate because of its chemical and thermal stability, no reaction with carbon, and ease of removal after carbonization by dissolving out in acidic solutions. was mixed with polyacrylonitrile (PAN) solution as a precursor of MgO with various weight ratios of /PAN. The average diameter of porous electrospun carbon fibers increased from 1.3 to 3 , as the to PAN weight ratio increased. During the stabilization step, was hydrolyzed to MgOHCl by heat treatment. At elevated temperature of 823 K for carbonization step, MgOHCl was decomposed to MgO. Specific surface area and pore structure of prepared electrospun carbon fibers were decided by weight ratio of /PAN. The amount of hydrogen storage increased with increase of specific surface area and micropore volume of prepared electrospun carbon fibers.

Shear thickening fluid (STF) is a non-Newtonian fluid featuring the increased viscosity upon high strain rate applied. Recently, STF-treated aramid fabrics have been researched to enhance the bulletproof efficiency maintaining the lightweight, however their shear properties including tow shearing, which significantly contribute to the bulletproof properties, have not been characterized, in particular under high shear strain rates. In this study, the shear properties of STF-treated aramid fabrics are characterized using a picture frame test. For this purpose, STF is prepared using polyethylene glycol and silica colloids and coated onto aramid fabrics. Varying the shear strain rate by controlling the pulling speed of the picture frame, the effect of STF on the shear properties of the aramid fabric is investigated. Finally, the shear properties of STF-treated aramid fabrics are predicted a multi-scale energy model and compared with the experiments. This prediction is then extended to cover such a high strain-rate situation as the bullet impacts, enabling to determine the mechanism behind the improved bulletproof performance of the STF-treated fabric.

Ferroelectricity is spontaneous electric polarization of a material without an external electric field and the polarization can be reversed by applying an external electric field as shown in Fig.1 (Kanzig, 1957; Lines & Glass, 1979). Because the spontaneous polarization of the material is changed by an external stimulus, ferroelectric materials are also piezoelectric and pyroelectric, when the stimuli are force and heat, respectively. Ferroelectric materials have non-linear polarization; thus, they can be used as capacitors with tunable capacitance. Moreover, the hysteresis effect of the spontaneous polarization of ferroelectric materials enables the application of ferroelectric random-access memories (RAMS) for computers and radio-frequency identification (RFID) cards (Buck, 1952). In addition, piezoelectric materials are used for high voltage power source, sensors, and actuators. In these systems, it is evident that ferroelectric and related materials are not used alone. For complete systems, other materials are required to compensate for the poor properties, such as the low conductivity of piezoelectric concrete, or to enhance their performance (Shifeng, 2009; Ishiwara 2009).