• Carbon letters
• /
• v.12 no.4
• /
• pp.207-217
• /
• 2011

We discuss the influence of few-walled carbon nanotubes (FWCNTs) treated with nitric acid and/or sulfuric acid on field emission characteristics. FWCNTs/tetraethyl orthosilicate (TEOS) thin film field emitters were fabricated by a spray method using FWCNTs/TEOS sol one-component solution onto indium tin oxide (ITO) glass. After thermal curing, they were found tightly adhered to the ITO glass, and after an activation process by a taping method, numerous FWCNTs were aligned preferentially in the vertical direction. Pristine FWCNT/TEOS-based field emitters revealed higher current density, lower turn-on field, and a higher field enhancement factor than the oxidized FWCNTs-based field emitters. However, the unstable dispersion of pristine FWCNT in TEOS/N,N-dimethylformamide solution was not applicable to the field emitter fabrication using a spray method. Although the field emitter of nitric acid-treated FWCNT showed slightly lower field emission characteristics, this could be improved by the introduction of metal nanoparticles or resistive layer coating. Thus, we can conclude that our spray method using nitric acid-treated FWCNT could be useful for fabricating a field emitter and offers several advantages compared to previously reported techniques such as chemical vapor deposition and screen printing.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.9
• /
• pp.2603-2606
• /
• 2010

Novel soluble triazoleimide oligomers terminated with arylacetylene terminated were synthesized by the Cu(I)-catalysed 1,3-dipolar cycloaddition polymerization of diazides and imide-containing dialkyne. Several molecular weight triazoleimide oligomers were prepared from diazide and dialkyne monomers with different stoichiometric combinations. The curing behaviors of the oligomers were tested by differential scanning calorimetry (DSC). The thermal properties of the cured products were evaluated by DSC and thermogravimetric analysis (TGA). These cured oligomers showed the glass transition temperature of about $225-235^{\circ}C$ and the decomposition temperature (at 5% weight loss) of about $385-393^{\circ}C$ in nitrogen.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.3
• /
• pp.909-916
• /
• 2013

Concrete containing lightly burnt MgO has long term expansibility. It also could compensate for the thermal shrinkage of mass concrete, because the hydration of MgO proceeds at a slow pace to long-term age. Thus, lightly burnt MgO has been applied to the construction of mass concrete such as dams. Recently, the expansion characteristics of MgO concrete with fly ash that could be applied to mass concrete for the reduction of hydration heat have been studied and however, limited studies on its durability. This study investigates the long-term durability characteristics of fly ash concrete with lightly burnt MgO. The durability tests on carbonation, freezing-thawing, diffusion of chloride, and resistance to sulfate attack were carried out for MgO concrete with curing for 360 days in submerged condition with different temperature of 20 and $50^{\circ}C$. The results reveal that MgO concrete shows a greater resistance of carbonation, diffusion of chloride, and resistance to sulfate attack. On the other hand the resistance of freezing-thawing was little influenced by MgO powder.

• Polymer(Korea)
• /
• v.28 no.2
• /
• pp.177-184
• /
• 2004

Polymer-clay nanocomposite containing the low amounts of clay shows improved physical, mechanical properties. In this study, allyl ester prepolymer was synthesised by reactions of the diallyl terephthalate monomers and the 1,3-butanediol monomers. Nanocomposites of allyl ester prepolymer and the two kinds of the organically layered silicate were prepared by using the intercalation method as well as the in-situ polymerization method using. By varying the amount of clay content, curing conditions, and feeding conditions. the nanocomposite was studied using X-ray diffraction. From XRD results, allyl ester-Cloisite 30 B nanocomposite made by the in-situ polymerization method shows better exfoliation behavior compared with the intercalation method. It can be said that the transesterification reaction between functional groups (-OH) of intercalant and monomers results in the increased gallery distance. Also mechanical and thermal properties indicate that the dispersity of clay is an important factor for improving physical properties of the nanocomposite.

• Polymer(Korea)
• /
• v.38 no.2
• /
• pp.171-179
• /
• 2014

Low temperature cure prepregs are being developed for use in the preparation of large-structured fiber-reinforced polymer (FRP) composites with good performance. Cure behavior and chemorheology of low temperature cure epoxy resin system, based on epoxy resin, curing agent, and accelerators, were investigated to provide a matrix resin suitable for the prepreg preparation. Characteristics of cure reaction were studied in both dynamic and isothermal conditions by means of differential scanning calorimetry and rheometry. The low temperature cure epoxy resin system suggested in this study as a matrix resin was curable at $80^{\circ}C$ for 3 h, and showed the gel times of 120 and 20 min at 80 and $90^{\circ}C$, respectively. Thermal and mechanical properties of the cured sample were almost the same as high temperature cure counterparts.

• Applied Chemistry for Engineering
• /
• v.17 no.6
• /
• pp.580-585
• /
• 2006

UV-thermal dually curable coating materials were prepared by the sol-gel method. Nano-sized colloidal boehmite was treated with various organo silane coupling agents. These materials could be well dispersed in various alcohols and relatively polar organic solvents such as tetrahydrofuran and acetonitrile. The coating films were prepared by a spin coating method on various substrates, which were characterized by FT-IR, Si/Al CP MAS NMR spectra, UV-Vis spectrophotometer, FE-SEM, Taber abraser, haze meter, and pencil hardness tester. The effects of molar ratio and types of silane coupling agents, curing method and ion-shower treatment were investigated. Dually curable coating method offered an optimally good quality film in both hardness and transmittance. The transparency and the hardness of the prepared films were increased with amounts of 3-(trimethoxysilyl)propylmethacrylate, and (3-glycidyloxypropyl)trimethoxysilane, respectively. The adhesion between coated layer and substrate could be enhanced by ion-shower treatment.

• Korean Chemical Engineering Research
• /
• v.55 no.6
• /
• pp.830-836
• /
• 2017

Hydrophilic coating solutions were prepared by reacting a silane coupling agent, GPTMS (3-glycidoxypropyl trimethoxysilane) with colloidal silica. Hydrophilic coating films were also obtained by depositing the hydrophilic coating solutions on polycarbonate substrates by spin-coating and subsequently by thermal curing at $120^{\circ}C$. During this process, the effect of average particle sizes of colloidal silica was studied on the properties of coating films. As a result, coating film, prepared from colloidal silica with average particle size of 25 nm, showed a low contact angle of $20^{\circ}$ and a good pencil hardness of H. On the other hand, coating films, prepared from colloidal silica with average particle sizes of 15 nm and 45 nm, exhibited high contact angles of $27^{\circ}$ and $36^{\circ}$ and pencil hardness of H and B, respectively.

• Polymer(Korea)
• /
• v.28 no.6
• /
• pp.494-501
• /
• 2004

A new alkali developable photosensitive poly(amic acid) (PAA-0) with transmittance at 400 nm was synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 2-(methacryloyloxy)ethyl-3,5-diamino-benzoate and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyl disiloxane in N-methyl-2-pyrrolidinone. Photosensitivity of the PAA-0 was investigated at 365-400 nm in the presence of a photoinitiator using a high pressure mercury lamp. The photo-cured poly(amic acid) was insoluble toward aqueous 2.38 wt% tetramethylammonium hydroxide solution. Negative pattern of the PAA-0 with 25 ${\mu}{\textrm}{m}$ resolution was obtained by developing with 2.38 wt% tetramethylammonium hydroxide solution after exposure of 600 mJ/$\textrm{cm}^2$ in the presence of 2,2-dimethoxy-2-phenyl-acetophenone as a photoinitiator. The patterned poly(amic acid) was converted to polyimide by thermal curing at 25$0^{\circ}C$ for 50 min, which showed chemical resistance against photoresist stripper as well as good transmittance at 400 nm.

• Korean Chemical Engineering Research
• /
• v.55 no.2
• /
• pp.247-252
• /
• 2017

Hydrophilic coating solutions were prepared by reacting a silane coupling agent, aminosilane with colloidal silica (15~20 nm in diameter). Hydrophilic coating films were also obtained by depositing the hydrophilic coating solutions on polycarbonate substrates by dip-coating and subsequently by thermal curing at $120^{\circ}C$. During this process, the effect of types of aminosilane was studied on the properties of coating films. As a result, coating films, prepared with 3-aminopropyltriethoxysilane (APTES) as aminosilane, showed contact angles of $25{\sim}44^{\circ}$ and a poor pencil hardness of B. On the other hand, coating films, prepared with 3-aminopropyltrimethoxysilane (APTMS) as aminosilane, exhibited contact angles of $26{\sim}37^{\circ}$ and a good pencil hardness of 2H.

• Polymer(Korea)
• /
• v.33 no.6
• /
• pp.544-550
• /
• 2009

In this study, we have designed [Epoxy/PEG] polymer gel electrolyte systems by thermal curing the mixtures of epoxy, PEG, imidazole catalyst, and a plasticizer of 1:1 ethylene carbonate and propylene carbonate in the presence of $LiPF_6$ salt. In order to enhance the poor mechanical property of the Corresponding [Epoxy/PEG] gel electrolyte PVdF-HFP was incorporated into the system. The ionic conductivities of the polymer gel electrolytes were related to the amount of PVdF-HFP in blends as well as the amount of liquid electrolyte. The optimized gel system showed room-temperature conductivities of $2.56\times10^{-3}S/cm$.