Dae‐Shik Seo

We have investigated the generation of the pretilt angles for nematic liquid crystal (5CB) aligned in the cells using rubbed polyimide (PI) films containing trifluoromethyl moieties as a function of rubbing strength (RS). In order to characterize the films, we have conducted an analysis of the surface atomic concentration of fluorine (F) relative to that of carbon (C), F/C(%) with an electron spectroscopy for chemical analysis (ESCA) in the shallow surface region at the depth of 3 and 12 nm. It

Abstract The pretilt angles generated in nematic liquid crystal (5CB) media that are disposed in sandwich type cells and oriented by using various orientation films are shown to depend both on the nature of the orientation films and the rubbing strengths in the following way: first, in a cell with alkyl branched polyimide (PI (1)) prepared by spin-coating, the obtained prettily angle 6P shows a giant peak reaching 51 degrees at the low rubbing strength (RS) region and then it decreases monotonic

We have studied the effect of the polymer tilt angle for pretilt angle generation in nematic liquid crystal, 4-cyano-4 ′ -n-penthylbiphenyl (5CB) on rubbed polyimide surfaces. The polymer tilt angle was determined by measuring induced optical retardation produced in rubbed polyimide (PI) surfaces by rubbing. We suggest that the polymer tilt angle is not related directly to the pretilt angle on rubbed PI surfaces by rubbing. We proposed a microscopic model of pretilt angle generation on rubbed PI

Abstract We have developed a high performance liquid crystal (LC) alignment layer of ultra‐thin single wall carbon nanotubes (SWNTs) and a conjugated block copolymer nanocomposite that is solution‐processible for conventional twisted nematic (TN) LC cells. The alignment layer is based on the non‐destructive solution dispersion of nanotubes with a poly(styrene‐ b ‐ paraphenylene) (PS‐ b ‐PPP) copolymer and subsequent spin coating, followed by conventional rubbing without a post‐annealing process.

We demonstrate self-aligned and high-performance liquid crystal (LC) systems doped with 1-dimensional (1D) chain-like clusters of CuInS(2) (CIS)-ZnS core-shell quantum dots (QDs). By changing the cell fabrication method of the LC-QD composites, we can selectively control the orientation of the LC molecules between the homogeneous and homeotropic states without conventional LC alignment layers. The homeotropic alignment of LCs was achieved by random dropcasting and the homogeneous alignment was p

A characterization of rubbed polystyrene (PS) film in terms of the optical retardation measurement as a function of the rubbing strength (RS) has been made, and the alignment capability of the rubbed PS films for a nematic liquid crystal (5CB) has been investigated by measuring anchoring strength and its temperature dependence. It is shown that the liquid crystal (LC) molecules orient homogeneously in a direction orthogonal to that of rubbing, the anchoring strength of the rubbed PS films at the

Abstract This article provides a review on the experimental aspects of the alignment of nematic liquid crystal (NLC) in the pretilted homogeneous form in the sandwich cells; most of the contents of this paper are the results of research done by the authors in these few years. For simplicity and convenience, we used nematic liquid crystal (5CB) only; however, we have explored several polymer orientation films such as alkylbranched or alkylbranchless polyimide (PI), PI-Langmuir-Blodgett (LB) films

AbstractWe report the doping effect of graphene quantum dots (QDs) in a nematic liquid crystal (NLC) device. The use of graphene QDs leads to improved electro-optical (EO) properties, such as faster response times and a decreased threshold voltage. A 14.8% reduction in the threshold voltage (3.165 V), a 30% decrease in the falling time (4.9 ms) and a 63.6% decrease in the rising time (2.4 ms) were observed for twisted nematic (TN) LC devices (LCDs) that were doped with QDs. We confirm that the d

We generated SnO2 alignment films with one of two liquid crystal (LC) molecular orientations: a stable, vertical orientation or a homogeneous orientation. We changed the molecular orientations by altering the growth temperature of radio-frequency (RF) magnetron sputtering. An ion-beam (IB) advanced system was used to achieve uniform alignment. We obtained two LC molecular orientations as demonstrated by the shift of the Sn 3d peaks and the altered-sub peaks of Sn2+, Sn4+ intensity on X-ray photo

The effect of rubbing on the polyimide (PI) Langmuir-Blodgett (LB) surface-alignment films has been successfully evaluated by observing the temperature dependence of the polar anchoring strength of nematic liquid crystal 4-cyano-4'-n-pentylbiphenyl (5CB). Upon rubbing, the PI-LB films showed a significant increase in the anchoring strength. The anchoring strength showed a nearly divergent decrease toward the clearing temperature, which is a manifestation of the diminished surface ordering, as pr

Abstract We explored the doping effects of zirconium dioxide (ZrO2) nanoparticles on the characteristics of liquid crystal (LC) devices. The electro-optic (EO) properties of LCs with various doping contents were changed. The addition of ZrO2 nanoparticles contributed to an improvement in EO properties in nematic LC cells such as low voltage operation and fast response time. The LC cells with 1.5 wt% ZrO2 nanoparticles showed the lowest threshold voltage (0.8 V) and the fastest response time (14.

In this article, we study the electro-optical (EO) properties of the homogeneous aligned nematic liquid crystal (N-LC) doped with cobalt oxide (Co3O4) nanoparticles (NPs). The EO characteristics of Co3O4 doped N-LC are higher performance, indicating lower threshold voltage (1.33 V), faster rising time (1.479 ms), and faster falling time (9.343 ms) than pure liquid crystal (LC) cells. We have demonstrated these results by investigating the relationship between dielectric constants and LC device p

We investigated solution-derived ZnO films as liquid crystal (LC) alignment layers via ion-beam (IB) irradiation. Solution processing was adopted to replace the sputtering method for the deposition of ZnO films as LC alignment layers. Uniform and homogeneous LC alignment was achieved, and a high-performance LC system was achieved using these substrates. X-ray photoelectron spectroscopy (XPS) analysis showed that surface reformation of ZnO films by annealing and IB irradiation affects the uniform

The effects of high pretilt angle are investigated on the polar anchoring energy of the nematic liquid crystal (NLC), 5CB, on rubbed polyimide (PI) films containing trifluoromethyl moieties. The pretilt angle of 5CB rapidly increases up to about 45° with the rubbing strength (RS). Also, the polar anchoring energy of 5CB initially increases with the RS for weak rubbing and then decreases. From these results, we determined the relationship between the pretilt angle and the anchoring energy on rubb

Abstract Atomic force microscope (AFM) observation has been made on rubbed polymer films for liquid crystal (LC) molecular orientation such as those of alkylbranched and branchless polyimide (PI) together with polystyrene (PS); other characterizations such as Fourier analysis and roughness evaluation have also been made. It has been investigated how these results of the characterization relate to the LC aligning capabilities such as microscopic texture and pretilt angle. It is shown that in a PI