Mechanical Rubbing Research Articles

Anisotropy and Raman absorption of the polyimide surface irradiated by the ion beam for liquid crystal alignment

In this paper, polyimide surfaces irradiated by an ion-beam for liquid crystal alignment are investigated by using atomic force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. A liquid crystal cell aligned homogeneously through the ion-beam exposure exhibits electro-optic switching behavior similar to that of a rubbing-aligned liquid crystal cell. However, we found that the surface morphology and bonding molecules of ion-beam-treated polyimide surfaces show properties very different from mechanically-rubbed ones. Experimental results show that optical anisotropy of ion-beam-treated polyimide surfaces results in the formation of hydrogenated amorphous carbon-like structure with a short main-chain, while mechanical rubbing has little effect on structural and compositional variations of polyimide layers.

Liquid crystal alignment on the two-directionally processed substrates: Comparison of mechanical rubbing and plasma beam alignment

Two-directional plasma beam processing or mechanical rubbing was used to investigate the orientations of liquid crystal (LC) molecules on polyimide (PI) and hydrogenated amorphous carbon films. Two-directional plasma beam processing exhibits better homogeneity than two-directional mechanical rubbing in the LC alignment. In the two-directional mechanical rubbing treatment, grid-like texture appears on the PI film, supporting that the direction of each rub is memorized. A phenomenon of rewriting LC alignment exhibits in the two-directional plasma beam processing. The effect of the first plasma beam scanning is erased by the second one in the two-directional plasma beam processing.

Polar and Azimuthal Alignment of a Nematic Liquid Crystal by Alkylsilane Self-Assembled Monolayers: Effects of Chain-Length and Mechanical Rubbing

Alkylsilane self-assembled monolayers (SAMs) on oxide substrates are commonly used as liquid crystal (LC) alignment layers. We have studied the effects of alkyl chain length, photolytic degradation, and mechanical rubbing on polar and azimuthal LC anchoring. Both gradient surfaces (fabricated using photolytic degradation of C18 SAMs) and unirradiated SAMs composed of short alkyl chains show abrupt transitions from homeotropic to tilted alignment as a function of degradation or chain length. In both cases, the transition from homeotropic to tilted anchoring corresponds to increasing wettability of the SAM surfaces. However, there is an offset in the critical contact angle for the transition on gradient vs unirradiated SAMs, suggesting that layer thickness is more relevant than wettability for LC alignment. Mechanical rubbing can induce azimuthal alignment along the rubbing direction for alignment layers sufficiently near the homeotropic-to-planar transition. Notably, mechanical rubbing causes a small but significant shift in the homeotropic-to-tilted transition, e.g., unrubbed C5 SAMs induce homeotropic anchoring, but the same surface after rubbing induces LC pretilt.

Electrons create a reaction

In an identification parade of chemical reactions using a single-electrode system, the charges generated by the mechanical rubbing of insulators are shown to be electrons rather than ions.

Surface nematic bistability at nanoimprinted topography

The azimuthal nematic bistability was realized by frustration between two azimuthally orthogonal anchoring axes induced by a nanoimprinted groove pattern and mechanical rubbing. The nematic bistability can be explained by the revised Berreman model of groove-induced surface anchoring, recently introduced by Fukuda et al. [Phys. Rev. Lett. 98, 187803 (2007)]. The azimuthal bistability can be tuned in arbitrary direction by changing the groove pitch and rubbing conditions. This simple combinatorial scheme may be considered as a practical candidate for bistable displays with tailored bistable directions required in various liquid crystal device modes.

Nursing stimulation is more than tactile sensation: It is a multisensory experience

Novel sensory experiences, particularly those associated with epochal developmental events like nursing alter cortical representation, affecting memory, perception and behavior. Functional MRI was used here to test whether the sensoricortical map of the ventrum is modified during lactation. Three stimuli were used to drive cortical activation in primiparous rats: natural, artificial suckling stimulation and general mechanical rubbing of the skin of the ventrum. These stimuli significantly activated the somatosensory cortex of dams. Of the three stimuli, artificial and pup suckling robustly activated much of the cerebrum, most notably the visual, auditory and olfactory cortices. Surprisingly, activation occurred even in the absence of pups, with artificial suckling. This finding suggests that incoming information from a single modality was sufficient to drive activity of others. Enhanced sensitivity across the cortical mantle during nursing may help the dam to perceive, process, and remember stimuli critical to the care and protection of her young.

Effects of Mechanical Rubbing on Surface Tension of Polyimide Thin Films

Polyimide thin films were produced by spin-coating a fluoride polyimide on glass substrates, followed by a mechanical rubbing. The application of mechanical rubbing to the polyimide thin films breaks the symmetry on the polymer surface and promotes the formation of a template for liquid crystal alignment. The surface tension of the rubbed polyimide is studied and found to decrease with an increase in rubbing strength. The polar part of the surface tension of the polyimide decreases significantly after the polymer surface is rubbed. The rubbed polyimide thin films exhibit anisotropic surface tension. The surface tension measured along the direction antiparallel to the rubbing direction is higher than that measured along the rubbing direction. The azimuthal variation in surface tension is direction-dependent on the rubbed polymer surfaces.

The Effect of Mechanical Rubbing on the Surface Free Energy of Poly(Vinyl) Alcohol Thin Films and the Contact Angle of a Liquid Crystal on the Rubbed Polymer Surfaces

The surface free energy of rubbed polyvinyl alcohol was studied. A mechanical rubbing to the polymer causes change in chemicophysical characteristics in outermost layer of the polymer. The increase of rubbing strength causes the decrease in the surface free energy of the polymer. The rubbed polymer thin films show a significant anisotropy in wettability. It is found that in the anti-rubbing-direction the contact angle of a liquid crystal is smaller. The increase of the rubbing strength leads to the decrease in the contact angle.

Abnormal Rubbing and Keratectasia

Hypotheses for the varied pathogenesis of the different forms of keratoconus have been outlined. Against this background, the possibility that abnormal rubbing causes or contributes to the development or progression of some forms of keratoconus has been examined. Circumstantial evidence that shows an association between abnormal rubbing and keratoconus is reviewed, and a wide range of different forms of abnormal rubbing is described. Also examined is evidence of several processes whereby the cornea appears to be, or could be, adversely affected by mechanical trauma caused by rubbing. Conditions that may increase susceptibility to mechanical rubbing trauma have been discussed. Evidence of a role for inflammatory mediators in the pathogenesis of keratoconus appears to void the description of keratoconus as a noninflammatory condition. When vigorous knuckle-rubbing forces are located on the normal peripheral cornea, the thinner or weakened cone apex may be exposed to high intraocular pressure distending forces that may tend to promote ectasia. It appears reasonable to conclude that abnormal rubbing is a cause of some types of keratoconus, not because all abnormal rubbing, or only abnormal rubbing, leads to the development of some types of keratoconus, but because abnormal rubbing may increase the likelihood of the development of some forms of keratoconus. Abnormal rubbing habits may commence or continue after routine contact lens wear is established. Any associated rubbing or contact lens trauma may contribute to the progression of keratoconus. The abnormal rubbing-ectasia association in keratoconus may extend to other forms of keratectasia, including that seen after laser in situ keratomileusis, for which a contributory abnormal rubbing hypothesis may be appropriate.

Pretilt angle control of carbon incorporated amorphous silicon oxide treated by ion beam irradiation

For unidirectional uniform alignment of liquid crystals (LCs), alignment layer materials (ALMs) such as oblique evaporated SiO, rubbed polyimide (PI), UV-irradiated photopolymer, and IB-irradiated diamond like carbon (DLC) have been investigated. To overcome the demerits of the mechanical rubbing process, we used ion beam (IB)-treated carbon incorporated hydrogenated amorphous silicon oxide (a-SiO x C y :H) for the planar alignment. In this paper, we suggest a-SiO x C y :H treated by IB irradiation increases pretilt angle. As the amount of incorporated carbon is increased, pretilt angle is increased because of the change of surface energy. In addition, IB conditions such as IB irradiation time, angle, and energy affect the pretilt angle.

The development of self-assembled liquid crystal display alignment layers

From simple pocket calculators to mobile telephones and liquid crystal display (LCD)-TV, over the past few decades, devices based on LCD technology have proliferated and can now be found in all conceivable aspects of everyday life. Although used in cutting-edge technology, it is surprising that a vital part in the construction of such displays, namely the alignment layer, relies essentially on a mechanical rubbing process, invented almost 100 years ago. In this paper efforts to develop alignment layers (also called command layers) by processes other than rubbing, namely self-assembly of molecular and macromolecular components will be discussed. Two topics will be presented: (i) tuneable command layers formed by stepwise assembling of siloxane oligomers and phthalocyanine dyes on indium tin oxide surfaces and (ii) command layers formed by self-assembly of porphyrin trimers. The potential use of these layers in sensor devices will also be mentioned.

Preface

Preface

Supramolecular command surfaces for liquid crystal alignment

AbstractDevices based on liquid crystal display technology, ranging from watches to flat panel displays, have proliferated over the past few decades and can now be found in all conceivable aspects of everyday life. It is surprising that a crucial part in the construction of such displays, namely the alignment layer, which dictates the surface alignment of mesogenic molecules, relies essentially on a mechanical rubbing process which was invented 100 years ago. In this paper, recent developments in the construction of alignment layers (also called command layers) based on the self‐assembly of molecular and macromolecular components are discussed. Two topics are highlighted: (i) tuneable layers formed by hierarchical assembly of siloxane oligomers and phthalocyanine dyes on indium‐tin‐oxide surfaces and (ii) command layers formed by self‐assembly of porphyrin trimers. Copyright © 2007 Society of Chemical Industry

Characterizations of Photo-Alignable Multi-Functioning Polyimide Material

For a potential application in thin-film-transistor liquid crystal display (TFT-LCD) manufacturing as a multi-functioning layer working as an overcoat layer and LC alignment layer simultaneously, a novel chloromethylated polyimide was synthesized. The electrical performances of liquid crystal (LC) cells with chloromethylated polyimide alignment layers were investigated. The polymer layer acted as a multifunctional layer that does role of planarization layer and photo-alignment layer with high photosensitivity and excellent thermal stability, simultaneously. The capacitance-voltage characteristics of LC cells fabricated from the photo-aligned layers were measured. The LC cells with rubbed and photo-aligned layer showed higher residual DC values and corresponding lower voltage holding ratios compared to the commercial alignment layer, probably due to the photo-induced ionic charges on the alignment layer. Mechanical rubbing of the extensively purified polymer layer did not generate much difference in residual DC when compared to commercial polyimides.

Fabrication of Highly Ordered Arrays of Nanoparticles by Mechanical Process

We have developed a new method of fabricating nanoparticles utilizing a mechanical rubbing process. Highly ordered arrays of Au nanoparticles with a diameter of 60 nm have been fabricated on a porous anodic alumina template. Pressure measurements during the mechanical rubbing process confirmed that these nanoparticles were formed only by a mechanical separation process. Our method can be applied to fabricate nanocapsules and has a wide range of applicability to materials that have never been controlled in the nanoscale.

Reverse tilt domains in liquid crystal cells with a splayed director configuration

When an electric field is applied to a nematic liquid crystal cell with splay alignment layers, which is realized by mechanical parallel rubbing, the system exhibits abnormal reverse tilt domains. Even though the system has pretilt angle due to symmetry breaking by rubbing, existence of singular point in a cell by splay geometry and shift of that by locally asymmetric pretilt angle configurations result in the abnormal reverse tilt domains. On the basis of Oseen-Frank theory, dependence of singular point upon the abnormal reverse tilt domains is theoretically investigated for a splay alignment liquid crystal cell. By using the Dickman’s Q-tensor method [SID Int. Symp. Digest Tech. Papers 24, 638 (1993)], liquid crystal director field is calculated for the splay-aligned liquid crystal cell that an electric field is applied to. We presume a model to explain the abnormal reverse tilt domains, and derive the conditions required for the generation and elimination of these domains.

Rubbing-induced anisotropy of long alkyl side chains at polyimide surfaces

Molecular organization at polyimide surfaces used as alignment layers in liquid crystal displays was investigated using vibrational sum frequency generation (SFG) spectroscopy. We focus on the orientation of the long alkyl side groups at the polymer surface using polarization-selected SFG spectra of the CH(3)- and CH(2)-stretch modes of the side chain. Mechanical rubbing and baking, an accepted industrial procedure used to produce pretilt of the liquid crystal, was found to induce pronounced azimuthal anisotropy in the orientational distribution of the alkyl side chains. Orientational analysis of the SFG vibrational spectra in terms of the azimuthal and tilt angles (in and out of plane, respectively) of the alkyl side chains shows their preferential tilt along the rubbing direction, with the azimuthal distribution narrower for stronger rubbed polymer samples.

Tribo-assisted reorientation of nanometre-thick Ag film in ultrahigh vacuum environment

The tribo-assisted reorientation of the 5-nm-thick Ag film with polycrystalline structure has been studied in an ultrahigh vacuum (UHV) environment. The film was prepared on an Si (1 1 1) √3 × √3-Ag surface in a UHV condition at a pressure less than 4 × 10−8 Pa. The friction coefficient of the film was 0.07 at the beginning of the sliding and decreased to 0.02 as the reciprocal sliding cycle proceeded. Reflection high-energy electron diffraction observation showed that the crystallographic orientation of the film surface was changed by the mechanical rubbing motion of the diamond pin. Scanning tunnelling microscopy observation showed that the Ag (1 1 1) plane on the worn surfaces of the film oriented parallel to the substrate surface. Synchrotron orbital-radiated X-ray diffraction showed that the Ag (1 1 1) domains in the layer increase as the number of slidings increase, which corresponded to the friction reduction process. This study has clarified the reorientation process of the Ag film with nanometric thickness.

LCD alignment layers. Controlling nematic domain properties

From simple pocket calculators, to mobile telephones and LCD-TV, over the past few decades devices based on liquid crystal display technology have proliferated into just about all conceivable aspects of everyday life. Although used in cutting-edge technology, it is surprising that a vital part in the construction of such displays relies essentially on a process invented almost 100 years ago. This essential part, the alignment layer, dictates the macroscopic uniform alignment of liquid crystalline molecules (mesogens) near its surface. The current method for manufacturing such layers is the mechanical rubbing of spin-coated polymers with a piece of velvet cloth. This very successful method is still at the basis of the production process of even the largest displays currently manufactured in industry. Unfortunately, the construction of ever larger displays with this technique is becoming a technological nightmare for engineers. Therefore, over the past decades, many alternatives to rubbing have been explored. This review will focus on advances towards achieving one of the most important goals in LCD technology: attaining rational control over the properties of nematic liquid crystal domains.

Measurement of contaminant removal from skin using a portable fluorescence scanning system

The residence time of particulate contamination on the human body is a factor that has an important impact on the accuracy of exposure assessment in the aftermath of an accidental release of radionuclides to the atmosphere. Measurements of particle clearance from human skin were made using an illumination system to excite fluorescence in labelled silica particles and a CCD camera and image processing system to detect this fluorescence. The illumination system consists of high-intensity light emitting diodes (LEDS) of suitable wavelengths arranged on a portable stand. The physically small size of the LEDs allows them to be positioned close to the fluorescing surface, thus maximising the fluorescent signal that can be obtained. The limit of detection was found to be 50 μg of tracer particle per cm 2. Experiments were carried out to determine the clearance rates of 10 μm and 3 μm particles from the skin. Results show that, in the absence of any mechanical rubbing of the skin, the clearance of particles from the skin followed an approximately exponential decay with a half-time of 1.5–7.8 h. Skin hairiness and degree of human movement were found, in addition to particle size, to have an important influence on particle fall-off rate.