Sung Hoon Jeong

PET fabric/polypyrrole composite with high electrical conductivity for EMI shielding

Abstract Polypyrrole (PPy) was polymerized chemically and electrochemically in sequence on a polyester (PET) woven fabric, giving rise to PET fabric/PPy composite with high electrical conductivity. In the chemical polymerization, pyrrole dissolved in an aqueous solution without or with polyvinyl alcohol as a surfactant was first sprayed on the PET fabric and oxidized by spraying an aqueous solution of an oxidant and a dopant. Electrochemical polymerization was carried out in an aqueous electrolyte solution by applying a constant current density to the PET fabric coated with chemically polymerized PPy and a stainless steel plate as the working and the counter electrodes, respectively. We investigated the effects of the chemical or the electrochemical polymerization conditions on the properties of the resulting composite such as surface morphology, electrical conductivity, environmental stability, and electromagnetic interference shielding effectiveness (EMI SE). We found that the composite shielded EMI by absorption as well as reflection and that EMI shielding through reflection increased with the electrical conductivity. The specific volume resistivity of the composite prepared in this study was extremely low as 0.2xa0Ωxa0cm and EMI SE was in the practically useful range of about 36xa0dB over a wide frequency range up to 1.5xa0GHz.

Electromagnetic interference shielding characteristics of fabric complexes coated with conductive polypyrrole and thermally evaporated Ag

Through the chemical coating of polypyrrole (PPy) doped with naphthalene sulfonic acid (NSA) on electrically insulating poly (ethylene terephthalate) (PET) woven fabric, PPy–NSA/PET complexes were synthesized. By using the electrochemical coating of PPy doped anthraquinone-2-sulfonic acid (AQSA) on PPy–NSA/PET complexes, PPy–AQSA/PPy–NSA/PET complexes were synthesized. The silver (Ag) was thermally vacuum evaporated on the surface of PPy–AQSA/PPy–NSA/PET complexes (Ag|PPy–AQSA/PPy–NSA/PET). Electromagnetic interference (EMI) shielding efficiency (SE) and dc conductivity (σdc) of fabric complexes were measured for EMI shielding characteristics and theoretical simulation. The measurement of EMI SE in the frequency range from 50 MHz to 1.5 GHz was performed by using ASTM D4935-99 method. The EMI shielding characteristics such as transmittance, reflectance and absorbance were obtained from the S (scattering)-parameter analysis. We control the contribution of the absorbance or the reflectance to total EMI SE through the coating of conductive PPy and the evaporation Ag.

Conductivity and EMI shielding efficiency of polypyrrole and metal compounds coated on (non) woven fabrics

We synthesized polypyrrole (PPy) and metal (AgPd) compounds coated on woven polyethylene teraphthalate (PET) and nonwoven polyester (PE) fabrics. PPy coated on PET or PE fabrics was chemically polymerized by using naphthalene sulfonic acid (NSA) as a dopant and electrochemically synthesized by using anthraquinon-2-sulfonic acid (AQSA) as a dopant. Temperature dependences of de conductivity [σ dc (T)] of PPy-NSA/fabric and PPy-AQSA/fabric complexes are compared. The electromagnetic interference (EMI) shielding efficiency (SE) of PPy/fabric complexes is in the range of 20 ∼ 80 dB depending on the thickness and conductivity.

Detecting Fabric Defects with Computer Vision and Fuzzy Rule Generation. Part II: Defect Identification by a Fuzzy Expert System

A new method for a fabric defect identifying system uses fuzzy inference in multicondition approximate reasoning and is capable of defect identification. The system uses fuzzy inference rules, and the membership function for these rules adopts a neural network approach. Only a small number of fuzzy inference rules are required to make the identifications of nondefect, slub (warp direction), slub (weft direction), nep, and composite defect. One fuzzy inference rule can replace many crisp rules. With this method, we can design a reliable system for identifying fabric defects. Experimental results with this approach have demonstrated an identification ability comparable to that of a human inspector.

Effect of Splitting and Finishing on Absorption/Adsorption Properties of Split Polyester Microfiber Fabrics

Nylon/polyester (N/P) conjugate fibers are split by alkaline hydrolysis and then finished with an antimicrobial agent, and the effect of splitting and finishing on the absorption/adsorption properties of the microfibers is studied. The split microfiber fabrics vary in weight loss and pore structure depending on the various splitting conditions. The absorption behavior of microfiber fabrics is analyzed by the degree of splitting, shrinkage, fabric density, and weight loss. Optimum splitting conditions are investigated for superior absorption rate and capacity. Even and complete splitting produces fine fibers closely packed in a parallel structure, which creates capillary channels that transport water into fabric treated at 140°C with about 10% weight loss. Values of adsorption, add-on (%), and good durability to repeated laundering and dry cleaning of the agent on the finished N/P microfiber fabrics are high, in contrast to a conventional fiber fabric. This is most likely due to the high surface area and surface irregularities caused by splitting and hydrolysis. The absorption capacity of the finished fabrics decreases because some pore spaces are filled with the adsorbed agent, while the absorption rate increases due to capillary sorption. The water absorption instrument newly devised for this study is an excellent measurement system. It is possible to measure the amount of water absorption with time, and to distinguish the differences in absorbency of the split N/P microfiber knitted fabrics, which have pore structures that vary in shape and size, created by and deformed during the splitting and finishing process.

Detecting Fabric Defects with Computer Vision and Fuzzy Rule Generation. Part I: Defect Classification by Image Processing

A fabric defect detecting system that uses an advanced method involving computer vision and image analysis is capable of defect classification. Image pre-processing techniques that enhance raw images are applied before defect classification by a K-means algorithm and statistical method. These generate a Bayes classifier from which a decision surface is created for a classification procedure that can categorize defective or nondefective regions. Defect detection of the test fabric image is implemented by the decision surface from the training fabric image. The advantages of using the decision surface are a reduction in the training step and the ability to rapidly classify fabric. Experimental results confirm the reliable and reasonable classification ability of the proposed system.

Mechanistic study for heterogeneous product growth in topochemical single-crystal-to-single-crystal transformation

Abstract Kinetic evaluation for the solid-state reaction of 1,4-dithiin/anthracene mixed single crystal proved the mechanism of the anisotropic heterogeneous propagation during the single-crystal-to-single-crystal transformation. The number of hydrogen bonds in the reactive molecule is directly correlated with the activation energy for the reaction––the ‘chain’ character of solid-state propagation being triggered by the breaking of the C–H⋯O hydrogen bonds.

Synthesis and keto–enol isomerism of 1-alkyl-2-methyl-5,6-dicyano-3-[2-(5-alkylamino-2,3-dicyanopyrazin-6-yl)-1-hydroxyethenyl]-pyrrolo[2,3-b]pyrazine

Abstract Reaction of 2-alkylamino-3-chloro-5,6-dicyanopyrazine 2 with 2,4-pentanedione in the presence of sodium hydride in benzene gave 2-methyl-3-acetyl-5,6-dicyanopyrrolo[2,3- b ]pyrazine, which was further reacted with 2 to give the keto–enol mixtures of 3-[1-hydroxy-2-(3-alkylamino-5,6-dicyanopyrazine)-ethen-2-yl]-5,6-dicyanopyrrolo[2,3- b ]pyrazine 4 . The keto-form of 4 is colorless in chloroform but red in dimethylsulfoxide (DMSO) as an enol-form. Their absorption spectra and electronic properties were correlated with their chemical structures.

Synthesis and characterization of novel blue azo‐dye derivatives containing acrylate group for dye‐based color filters

— Even though dyes have a fine resolution and good chromaticities, they are not widely used as coloring materials for color filters (CFs) due to their low thermal stability and chemical resistance. A series of azo-dye derivatives, which consist of two cross-linkable acrylate or methacrylate groups to improve thermal and chemical properties, have been synthesized and used to fabricate color filters. The spectral properties and chemical/thermal stabilities of the fabricated CFs were investigated by comparing dye-based CFs, without a complicated dispersion process, but with pigment-based CFs using dispersed pigment. Also, more properties including the development test and surface morphologies lithographic properties were studied. The synthesized azo dyes were characterized by elemental analysis, UV-visible spectra, IR, mass, and 1H-NMR spectra.