Sang-Keuk Lee

Liquid Crystal Alignment Effects on SiNx Thin Film Layers Treated by Ion-Beam Irradiation

Nematic liquid crystal (NLC) alignment effects on SiNx thin film layers treated by ion-beam irradiation for three types of N ratio were successfully studied for the first time. The SiNx thin film was deposited by plasma-enhanced chemical vapor deposition using three types of N ratio. To characterize the film, atomic force microscopy was performed. Good LC aligning capabilities on the SiNx thin film treated by ion-beam irradiation for all N ratios can be achieved. The low pretilt angle for an NLC on the SiNx thin film treated by ion-beam irradiation was observed and could be adopted in planar alignment liquid crystal display applications as in-plane switching and fringe-field switching modes.

Electro optical performance characteristic of in-plane switching cell treated on nitrogen-doped diamond-like carbon thin film surfaces by ion beam alignment

The nematic liquid crystal (NLC) alignment capability achieved by ion beam alignment on a nitrogen-doped diamond-like carbon (NDLC) thin film was investigated. To characterize the NDLC thin film, we analyzed the obtained atomic force microscopy (AFM) images and pretilt angle. Moreover, we investigated the electro optical (EO) performance characteristics of ion-beam-aligned in-plane switching (IPS) cell with the NDLC thin film. The EO performance characteristics of the ion-beam-aligned IPS cell were observed by ion beam exposure on the NDLC thin film and compared with those of a rubbing aligned polyimide (PI) thin film. Finally, similarly prominent capacitance–voltage (C–V) characteristics were achieved in the ion-beam-aligned NDLC thin film compared with the rubbing-aligned PI thin film.

Washing effects on the anchoring energy and surface order parameter on rubbed polymer surfaces containing the trifluoromethyl moiety

The washing effects on liquid crystal (LC) alignment capability in a NLC, 4-n-pentyl-4′-cyanobiphenyl (5CB), on a rubbed polyimide (PI) surface containing the trifluoromethyl moiety were studied. The extrapolation length d e of 5CB on the rubbed PI surface decreases with the rubbing strength RS. Also, the large extrapolation length d e of 5CB for washing with IPA was measured at RS=114 mm. The polar anchoring energy of 5CB on the rubbed PI surface was decreased by the washing process; it increased with the rubbing strength RS on the PI surface. The surface order parameter S S of 5CB for all the washing processes is smaller than for the non-washing process. Consequently, the polar anchoring energy and surface order parameter S s in 5CB are largely attributed to washing effects.

Dielectric Anisotropy Effects on Pretilt Angle Generation for Nematic Liquid Crystals on a Polymer Layer

Generation of the pretilt angle in nematic liquid crystal (NLC) with negative dielectric anisotropy and cyano (CN) mixtures on a rubbed polyimide (PI) surface was studied. The pretilt angle of negative type NLC generated was larger than that of the positive type NLC on the rubbed PI surface for homogeneous alignment. However, the pretilt angle of negative type NLC generated was lower than that of the positive type NLC on the rubbed PI surface for homeotropic alignment. The different mechanisms of LC pretilt angle for homeotropic and homogeneous alignment can be observed. The pretilt angle increases with cyano content on the rubbed PI surface for homogeneous alignment and then saturates with further addition.

The Fracture Distribution in ITO Coating with Compressive Bending Stress on Polymer Substrates

In this paper, we investigated the fracture distribution in indium-tin-oxide (ITO) coating with compressive bending stress on polymer. Under compressive strain, the ITO island delaminates, buckles and cracks. As the mechanical compressive stress increases, the buckling width of ITO seems to be increased. These created cracks are related to well-defined distribution of mechanical stress in ITO island-arrays. We related. mechanical bending stress to crack distribution and derived theoretical equation of position-dependent bending stress. And, we verified the bending stress`s magnitude to crack distribution observed from optical photographs.

Liquid Crystal Orientation Mechanism and Tilt Angle Transition Behavior on Homeotropic Polymer Surfaces due to Ion Beam Treatment

We examined the transition behavior of the tilt angle on homeotropic polyimide (PI) surfaces as a function of ion beam (IB) irradiation incident angle. We also investigated the liquid crystal (LC) orientation mechanism by X-ray photoelectron spectroscopy. The tilt angles of the IB-irradiated PI surfaces were controlled in the range of 82–90° as functions of IB irradiation time and incident angle. The largest deviation from the homeotropic alignment was achieved at an IB incident angle of 45°. The plot of the atomic percentage of C–O binding energy versus IB incident angle was shaped like an upward-pointing triangle, while that of the C=O binding energy versus IB incident angle was the reverse. The tilt angle behavior as a function of IB incident angle was similar to the atomic percentage behavior. The LC alignment with IB irradiation was due to the dipole–dipole interaction between the C–O single bonds and the LC molecules. An excellent voltage–transmittance curve for the vertical alignment (VA)-LC cells was observed with a threshold voltage behavior related to the tilt angle. Suitable response time characteristics were measured for VA-LC cells treated with IB irradiation.

Dispersion Properties of Epoxy-layered Silicate Nanocomposites Using Homogenizer

Department of Electrical Electronic Engineering, Joongbu University, Geumsan 312-702, Korea (Received December 24, 2012; Revised January 18, 2013; Accepted January 21, 2013)Abstract: This paper presents a study on the dispersion effect of the X-Ray diffraction, glass transition and DMA properties of organic modifier clay/epoxy nanocomposites produced in a homogenizer . Several experiments were conducted including different types of dispersion condition with varying processing conditions such as homogenizer rotor speed and applied time of homogenizer. The effects of these variables on the dispersion properties of nanocomposites were then studied. In order to fully understand the experimental results, a X-ray diffraction, DSC and DMA were used to investigate the effect of above mentioned variables on microstructure and intercalation/exfoliation of organic modifier clay/epoxy nanocomposites. The results from this work could be used to determine the best processing condition to obtain appropriate levels of d-spacing, glasss transition temperature and storage modulus in organic modifier clay/epoxy nanocomposites.Keywords: Homogenizer, Epoxy-organic modifier clay nanocomposites, X-ray diffraction, Glass transition temperature, Dispersion condition, Intercalation/exfoliation

Tilt Angle Generation in NLC on Homeotropic Polymer Surface with Ion Beam Irradiation as a Function of Incident Angle

We have studied the tilt angle generation on the homeotropic polyimide (PI) surface using a low intensity ion beam source as a function of incident angle. An excellent LC alignment of nematic liquid crystal (NLC) on the PI surface with ion beam exposure for all incident angles was observed. The tilt angle of NLC on the homeotropic PI surface for all incident angles was from 90 to 88 degree was observed. Also the tilt angle of NLC on the homeotropic PI surface with ion beam exposure of 400 eV had a tendency to increase as ion beam energy incident angle become more instance from 45 degree. Finally, a good LC alignment thermal stability on the homeotropic PI surface with ion beam exposure can be achieved.

LC Orientation Characteristics Treated on Organic Hybrid Overcoat Layer with Ion Beam Irradiation

We have studied the liquid crystal (LC) orientation behavior on the organic hybrid overcoat layer with ion beam irradiation. Excellent LC alignments of the nematic liquid crystal (NLC) on the ion beam irradiated organic hybrid overcoat layers were observed in various intensities above 600 eV. Pretilt angles of the NLC on the organic hybrid overcoat layers for all ion beam energy intensities were observed from 0.2 to 0.5 degrees. Also, we used the atomic force microscopy (AFM) images for measuring the roughness of the organic hybrid overcoat layers with ion beam irradiation before and after. The surface of organic hybrid overcoat layers was leveled off by the ion beam irradiation. Finally, a good LC alignment thermal stability on the organic hybrid overcoat layer with ion beam irradiation can be achieved.

Annealing Behavior of Pretilt Angles on Polyimide Surface with Rubbing and Ion Beam Irradiation

We have studied the liquid crystal (LC) alignment, the pretilt angle generation, and the annealing behavior for a nematic liquid crystal (NLC) on the homogeneous polyimide (PI) surfaces by using the rubbing method and the ion beam (IB) method. An excellent LC alignment of the NLC on the PI surface with rubbing and IB irradiation were observed. The pretilt angle of NLC on the homogeneous PI surface for the rubbing method is decreased from to as rubbing time is increased, that of the for the IB irradiation method is decreased from to as the time of IB irradiation is increased. After the annealing, the pretilt angles of the rubbed PI surfaces increased up to , these of the IB irradiated PI surfaces little increased. It is considered the side chain of the rubbed PI show the its abilities of the original capacities, while the side chain of the IB irradiated PI cannot show the its abilities of the original capacities due to the IB has already destroyed the side chain of the PI.