• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.11 no.10
• /
• pp.878-884
• /
• 1998

We have investigated that the monodomain alignment of nematic liquid crystal (NLC) is obtained with polarized ultraviolet(PUV) light irradiation on polyimide (PI) surface. The LC alignment capability increases with increasing the UV light irradiation time. The polarized UV light irradiation on oblique angle of 60。 irradiated on PI surface rotated by 90。 at 10 min. after being normally irradiated on PI surface at 30 min., the generated pretilt angle of NLC is about 2.5。. The pretilt angle of NLC is attributed to the interaction between the LC molecules and the asymmetric triangular structure of polymer surface due to photo-depolymerization of polymer with the oblique UV light on PI surface. The voltage -transmittance and response time characteristics of photo-aligned twisted nematic (TN)-LCD with UV light irradiation time 60 min. were almost same in comparison with the rubbing-treated TN-LCD.

• Korean Journal of Materials Research
• /
• v.14 no.6
• /
• pp.407-412
• /
• 2004

Photo decomposition of gas phase benzene by $TiO_2$ thin films chemically deposited on alumina balls were investigated under UV irradiation. Photo decomposition rates were measured in real time during the reaction using a photo ionization detector, which ionizes C-H bonding of benzene molecules and then converts into volatile organic compounds (VOCs) concentrations. From the measuring results, the VOCs concentration increased instantly when IN irradiated because C-H bonds of benzene molecules strongly absorbed on the surface of $TiO_2$ films before the IN irradiation was destroyed by photo decomposition. After that, the VOCs concentration decreased with increasing surface area of $TiO_2$ and reaction time under the IN irradiation. At the optimal conditions for the photo decomposition of gas phase benzene, the reaction rate of the photo decomposition for high concentrations (over 60 ppm) was slow but that of relatively low concentration (under 60 ppm) was fast, due to limited surface area of $TiO_2$ thin films for the reaction. Thus, it is concluded that the photo decomposition rate was mainly affected by the surface area of $TiO_2$ or absorption reaction.

• Polymer(Korea)
• /
• v.36 no.2
• /
• pp.145-148
• /
• 2012

The effects of the linearly polarized UV (LPUV) irradiation and thermal treatment of a photo-degradable polyimide (CBDA-ODA) alignment layer (AL) on its AL properties, liquid crystal (LC) alignment, and LCD characteristics have been investigated. The best quality of LC photo-alignment have been induced by the LPUV-irradiation with much (about 5~10 times) less dosage than that generating the maximum anisotropy of the AL. A thermal treatment of the LPUV-irradiated AL has effectively removed the undesirable, low-M.W. fragments of the AL generated during the photo-decomposition and increased the stability of the AL, which has resulted in improvement of the LC alignment and the LCD property.

• Proceedings of the KIEE Conference
• /
• 1999.07d
• /
• pp.1759-1761
• /
• 1999

The generation of pretilt in nematic liquid crystal(NLC)and electro-optical(EO) characteristics of photo-aligned twisted nematic (TN)-LCD with oblique p-polarized ultraviolet (UV) light irradiation on the two kinds of the soluble polyimide (PI) surfaces containing trifluoromethyl moieties were investigated. The generated pretilt angle of NLC is about $2.5^{\circ}$ with p-polarized UV light irradiation of $20^{\circ}$ on PI-3 surface at 20 min.; However pretilt angle of about $0.5^{\circ}$ are observed on PI-1 and PI-2 surfaces. The generated pretilt angle of NLC on PI-3 surface may be attributed to the trifluoromethyl moieties attached to the lateral benzene rings. The voltage-transmittance and response time characteristics of photo-aligned TN-LCD with p-polarized UV light irradiation of $20^{\circ}$ on PI-1 surfaceat at 20 min were almost same in comparison with the rubbing-aligned TN-LCD. However, the high threshold voltage and slow response are observed on PI-3 surface. Also, the decay time $\tau_d$ of photo-aligned TN-LCD is attributed to the anchoring energy of NLC.

• Journal of Photoscience
• /
• v.9 no.2
• /
• pp.138-141
• /
• 2002

A photo-labile compound which is bioinactive but, upon irradiation with light, yields bioactive species is called as "caged compound". Photolysis of caged compounds generating bioactive species, has become a general method to produce a desired amounts of bioactive species in the specific time interval at the desired place or area of the target biological systems. For this purpose, we designed and synthesized caged hydroxyl radical., "Photo-Fenton Reagent" NP-IIl. NP-IIl has a strong absorption maximum at 377 nm and yields hydroxyl radicals upon UV light irradiation. The antioxidant activity of the ${\alpha}$ -lipoic acid and other naturally occurring compounds has been examined by using NP-IIl as a molecular probe. For example, upon photoirradiation of NP-lII with BSA or apolipoprotein of human low density (LDL), the significant oxidative modifications were observed in both cases. The oxidation was completely suppressed in the presence of ${\alpha}$-lipoic acid, which clearly demonstrates the strong hydroxyl radical scavenging activity of ${\alpha}$-lipoic acid. Other applications of NP-lII will also be described

• Journal of Photoscience
• /
• v.7 no.2
• /
• pp.47-52
• /
• 2000

The copolymmers of N, N-dimethylaminoethyl methacrylate(DAEM) and N-arylmethacrylamide (AMA) were prepared, and their photochemical properties as a negative photoresist were studied by the measurements of insoluble fraction, and by UV and IR absorption spectral changes. These copolymers are soluble in DMF, actone, methanol, of acidic buffer solutions. Solubility of these copolymer films in the vuffer solutions increased with the amount of DAEM units in the copolymer and decreased with the pH value. The insoluble fraction of the copolymer films in the buffer solution of pH 4 of in methanol increased with irradiation time and the amount of AMA units in the copolymer. UV and IR spectral changes indicated that not only photo-crosslinking but also the photo-Fries rearrangement took place upon irradiation with a 254nm UV light.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.7
• /
• pp.627-633
• /
• 2002

Many isolated featureless domains were explicitly observed even at the air-water interface. We measured the surface pressure shift originating from the photo-isomerization of azobenzene units on the periphery of dendrimers. The maximum surface pressure was gradual1y increased and saturated by cyclic compression and decompression. By irradiation of 365 [nm] light, the surface pressure was increased, which was originated by the photo-isomerization process of the azobenzene group on the periphery from trans to cia form. The increase of the dipole moment ($\mu$), which may increase the interaction among Azo dendrimer molecules, made an important role on surface pressure shift. From the absorbance spectrum by UV irradiation and heat treatment, we can see that the absorbance in the UV region decreases with the increase of the UV irradiation time, but the peak at 350 m, characteristic of dendrimers in the LB monolayers, was not shifted until four irradiation cycles. This suggests that optical behavior and morphological change are affected by the functional group and the symmetric chain.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.7
• /
• pp.1031-1034
• /
• 2002

• Journal of Korean Society of Water and Wastewater
• /
• v.20 no.5
• /
• pp.755-761
• /
• 2006

Recently, there is growing interest in ultraviolet (UV) irradiation as a disinfection technic in drinking water production due to its effectiveness to inactivate microorganisms such as Crytosporidium parvum without forming disinfection byproducts. However, UV disinfection is known for its drawback such as photoreactivation. Despite many works concerning the photoreactivation, most of works were focused on indicator or non pathogenic microorganisms. The objective of this study is to examine the photoreactivation of Pseudomonas aeruginosa which is an opportunistic pathogen as UV radiation by LP and MP UV lamp was applied. The result showed that P. aeruginosa had high photo repair efficiency regardless of the type of UV irradiation. Both of the effective log repair values of LP and MP UV irradiation were found approximately 2.6 log. In addition, photo repaired P. aeruginosa was not significantly different in forming biofilm in comparison with non treated P. aeruginosa.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.06a
• /
• pp.259-262
• /
• 1998

The liquid crystal (LC) alignment and pretilt angle generation using photo-alignment method were investigated in this study. We obtained that the monodomain alignment of nematic(N) LC increases with increasing irradiation time in a cell with linearly polarized ultraviolet (LPUV) light irradiation on polyimide (Pl) surfaces. We consider that the monodomain alignment is able to be anisotropic dispersion force due to photo-depolymerization of polymer with LPUV light irradiation on Pl surface. Also, we observed that the uniform alignment of NLC is obtained in a cell with normally LPUV light irradiated on Pl surface at 30 min. and then oblique LPUV is secondly irradiated on Pl surfaces rotated by 90$^{\circ}$. The pretilt angle of NLC is generated about 1.5$^{\circ}$ with oblique angle 60$^{\circ}$.