Phil-Hyun Kang

Effects of surface characteristics of dielectric layers on polymer thin-film transistors obtained by spray methods

The effect of surface characteristics of dielectric layers on the molecular orientation and device performance of sprayed organic field-effect transistors (OFETs) obtained by a novel solvent-assisted post-treatment, called the solvent-sprayed overlayer (SSO) method, were investigated. The OFETs were fabricated by the spray method using regioregular poly(3-hexylthiophene) (RR-P3HT) as an active material. The SSO treatment was applied on the as-sprayed active layers to arrange the molecular ordering. Bare thin SiO(2) layers and octadecyltrichlorosilane (OTS)-treated SiO(2) (OTS-SiO(2)) were employed as the dielectric materials. The resulting chain orientation, crystallinity, and device performance were correlated as a function of SSO treatment and dielectric layers. The intrinsic limitation of spray methods for polymer film formation was overcome regardless of the type of dielectric layer using the SSO treatment. The orientation direction of RR-P3HT was controlled by SSO treatment to an edge-on dominant orientation that is preferential for charge transport, regardless of the type of dielectric layer. The crystal growth was further enhanced on the OTS-SiO(2) layers because of the reduced nucleation sites. These effects were successfully reflected in the device performance, including an orders-of-magnitude increase in charge mobility. The SSO method is a powerful external treatment method for reorienting the molecular ordering of solidified active films of OFETs to the preferential edge-on packing. The growth of crystals was further optimized by controlling the surface characteristics of the dielectric layers. The purpose of this study was to find the full capabilities of the SSO treatment method that will facilitate the development of high-throughput, large-area organic electronic device manufacturing.

Preparation of nanocellulose from a kenaf core using E-beam irradiation and acid hydrolysis

Abstract Recently, the rapidly expanding use of nanocellulose has been focused on abundant, light-weight, sustainable, biodegradable, and potential materials. This paper presents a summary of the findings of an exploratory study conducted to investigate the facile processing of nanocellulose from a kenaf core using electron beam irradiation. In this study, nanocellulose was produced by first isolating cellulose from a kenaf core, and then conducting electron beam irradiation and acid hydrolysis followed by a TEM analysis to confirm the form of the nanocellulose fibers. As the dose of electron beam irradiation increased, the crystallinity, molecular weight, polydispersity, and decomposition temperature of cellulose decreased. Such results influenced the size distribution and yield in acid hydrolysis; as the absorbed dose and acid hydrolysis reaction time increased, the yield of nanocellulose decreased while the size distribution became narrower.

Electron beam irradiation and dilute alkali pretreatment for improving saccharification of rice straw

Rice straw is one of the most abundant and low-cost biomasses available in the world. Thus, the rice straw as a potential candidate for future energy and chemical resource has been intensively studied in order to use as the current fossil fuels. However, the structure of rice straw makes it difficult to hydrolyze into fermentable sugars owing to the cellulose in rice straw being tightly surrounded by hemicellulose and lignin, thus pretreatment of rice straw is needed for this process. In the present study, an alkali pretreatment method assisted by electron beam irradiation was investigated to improve the saccharification in an enzymatic hydrolysis yield. After pretreatment, cellulose in rice straw was increased from 39.5 to 71.1%, and lignin decreased from 19.5 to 6.4%. The sugar yield of the pretreated rice straw increased with an increase in irradiation dose. The results of XRD and Fourier transform infrared spectroscopy analyses showed that the properties of the straw were changed by this pretreatment, which favored the following enzymatic hydrolysis.

Isolation and characterization of nanocrystalline cellulose from different precursor materials

Nanocrytalline cellulose (NCC) was isolated using cellulose extracted from two different precursor materials: Eucalyptus globulus and rice straw. The two ground precursor materials were autoclaved with a 10 % NaOH solution at 120 °C for 3 h. The alkali-treated precursor materials were bleached using sodium chlorite/acetic acid and sodium hypochlorite. The bleached precursor materials were acid-hydrolyzed in 65 % (w/w) sulfuric acid at 45 °C for 30-120 min. The changes in the chemical composition of the two precursor materials were studied before and after bleaching by Fourier transform infrared spectroscopy according to the NREL report and TAPPI standards. Hydrolyzates were characterized by X-ray diffractometry, thermogravimetric analysis, Zeta-potential analysis, and transmission electron microscopy. The results revealed that the physical properties of NCC were strongly dependent on the acid-hydrolysis time.

Preparation of Ag nanoparticles on PAN/TiO2 nanofibers and their photocatalytic and antibacterial properties

Polyacrylonitrile/titania (PAN/TiO2) nanofibrous mats were prepared by an electrospinning method and silver nanoparticles were deposited by electron beam (e‐beam) irradiation of silver ions in aqueous solutions. The morphology of the electrospun fibers was characterized by SEM analysis. The deposition of silver particles was not of a uniform coverage on the PAN/TiO2 surface, but of a heterogeneous growth of the silver particles on the PAN/TiO2 surface. The photocatalytic efficiency of the composites against methylene blue dye in an aqueous solution improved and the actibacterial activity against E. coli and S. aureus was found to increase with the silver nanoparticles being induced.

Effects of electron beam irradiation on polyamide 12 with fiberglass reinforcement

In the present study, the effects of electron beam irradiation of polyamide 12 (PA12) with fiberglass reinforcement on the thermal and wear properties were investigated. Electron beam irradiation of PA 12 was carried out over a range of irradiation doses (100–600 kGy) in air. The gel formation in the presence of a curing agent was dependent on the radiation doses. The thermal properties of irradiated PA 12 were studied in the temperature region 50–250° C to observe the changes in the melting point with radiation dose. The dimensional stability was significantly increased by electron beam irradiation and the related crosslinking of the PA 12.