Rubbing Treatment Research Articles

Flow-induced high pretilt alignment of liquid crystalline molecules on polymer surface evaluated by optical second-harmonic generation

Abstract The alignment of liquid crystalline molecules at the interface between liquid crystal and polyimide surface was investigated on the basis of an optical second-harmonic generation method. It was confirmed for the first time that a uniform alignment of liquid crystalline molecules with a pretilt of about 10° was achieved by simply flowing the liquid crystal on the polyimide-coated substrate surface which produced no pretilt by a standard rubbing treatment.

A Radial Molecular Orientation Using a Flow-Induced Aligning Method in a Nematic Liquid Crystal Cell

The radially symmetrical molecular orientation is demonstrated by using a flow-induced aligning method in a nematic liquid crystal (LC) on a PVA-coated substrate without a rubbing treatment. The radial molecular orientation of good quality is obtained as compared with the LC cell using a radial rubbing treatment. The diameter of the area with the radial orientation is above five times larger than that obtained by a memory effect of molecular orientation in an electric field produced by a hole-patterned electrode structure. A radially and homogeneously aligned LC cell is prepared, and a molecular orientation state and polarization converting properties are clarified by observations of transmission images and measurements of transmission properties. The effect of a chiral dopant in the LC cell is also investigated, and it is found that the chiral pitch of LC materials can be determined by a rotation angle of disclination line.

Study on the Director Configuration and Display Properties of Amorphous Nematic Liquid Crystal Displays with Different Values of d/p

Abstract In this paper, based on experimental results, a model of the director coniiguration of amorphous nematic liquid crystal disphys(a-n-LCDs) was related. From our study we find that the a-n-LCDs are characterized with disordered surface alignment. Based on the modeling, a detailed analysis of the influence of parameters on display properties is given out, and the discussion shows that d/p=1/4 is not a strict condition for display use of a-n-LCDs, even though d/p > 112, good E-O property for display use can also be obtained. The a-n-LCDs supply a way to avoid the rubbing treatment and exhbit display properties of good color reproduction and wide viewing angle. When the value of d/p is increased, the threshold E-O curves become steep, and this supplies the novel n-LCDs with a high-multiplexing capacity.

Expression of several genes encoding chaperone proteins in response to mechanical perturbation inBryonia dioica internodes

Mechanical stress exerted on youngBryonia dioica internodes which resulted in reduced elongation and increased radial expansion induced a rapid and transient increase in specific mRNAs. Hybridizations were performed using ubiquitin, cyclophilin and heat-shock protein cDNAs as probes on RNA extracted at successive time intervals in control and rubbed internodes. Changes in ubiquitin and cyclophilin were rapidly enhanced after mechanical perturbation. Levels of mRNAs reached a maximum 0.5 h and 1.5 h after rubbing and then decreased. The heat shock protein gene was constitutively expressed; it was however slightly stimulated following the rubbing treatment. All the three genes encoded for molecular chaperones and they were regulated in response to environmental stimuli. The role of chaperones was discussed with regard to the plant response to several natural stresses.

Polyimide film containing ultra-fine particles

We have succedded in fabricating a polyimide film with a molecular alignment superior to that obtainable by the conventional rubbing treatment. This phenomenon is realized by means of the dispersion of ultra-fine particles such as carbon and titanium dioxide in the polyimide precursor prior to the fabrication of the polyimide film and the rubbing treatment. The molecular alignment was evaluated with birefringence and infrared dichroism measurements. Further experiments establishe that the adsorption of polyimide molecules on ultra-fine particles is a significant factor in achieving a large orientational anisotropy. A model of the alignment is presented in which the rubbing treatment induces the particles to traverse the surface of the film, causing polyimide molecules adsorbed on them to be elongated in the rubbing direction. A potential application of oriented polymide films is the homogeneous alignment of nematic and smectic liquid crystals.

Machanical Durability of Water-Repellent Film on Glass

Water-repellent films were applied on various glass substrates at room temperature using fluoroalkyl isocyanate silane as a starting material. These waterrepellent glasses were examined on initial water-repellent property and its mechanical durability against rubbing treatment. It was found that the difference in the initial water-repellent property among them was hardly discernible, but the mechanical durability was dependent on the surface state of glass substrates. The dependence of the mechanical durability on the substrate can be explained by the density of the absorbed waterrepellent molecules associated with the number of adsorption sites such as silanol group at the surface of glass substrates. Furthermore, another reason for the improvement of the mechanical durability is strong adhesion of the film to the substrate due to the formation of siloxane bond at the film/substrate interface. The durability mechanisms are described in detail based on the results of XPS, static SIMS and IR analyses.

Incidence of Physical Damage on Peach and Nectarine Skin Discoloration Development: Anatomical Studies

Skin discoloration (SD) formation in peach [Prunus persica (L.) Batsch] and nectarine [Prunus persica (L.) Batsch, var. nectarine] was related to physical damage (abrasion) to the fruit during fruit handling (harvest and hauling operations) within the orchard and during transport to the packinghouse. Vibration and rubbing treatments increased SD formation indicating that tissue damage is involved in SD formation. Anatomical studies comparing sound and SD-injured tissues done by scanning electron and light microscopy indicated that very-low-intensity physical damage could induce brown and/or black spots because of cell disruption in the epidermal and hypodermal layers. The fact that injury was specific to the exocarp tissues (cuticle, epidermis, and hypodermis), and that mesocarp tissue located below the exocarp cells remained sound and turgid, indicated that abrasion injury is associated with SD. Similar types of visible and anatomical injury characteristics were induced by a rubbing treatment, demonstrating that physical abrasion damage affecting just exocarp cells was enough to induce SD:

Effect of rubbing on the molecular orientation within polyimide orienting layers of liquid-crystal displays

The influence of various rubbing parameters on the molecular reorientation of thin polyimide orienting layers, used to align liquid-crystal (LC) molecules within liquid-crystal displays, has been studied. For this purpose the optical phase retardation in the polymer layer, explicitly induced during the rubbing treatment, was determined. The observed rubbing-induced phase retardation can directly be related to a molecular orientation within the polymer orienting layer, as could be shown by infrared dichroism studies. Furthermore, it is found that the top of the polymer layer, directly contacting the rubbing cloth during the actual rubbing process, is almost instantaneously oriented to a certain maximum value as soon as the rubbing is started. Additional or stronger rubbing has no detectable influence on the orientation within the top layer. Increasing the rubbing density or the rubbing pressure only results in an increase of the penetration depth of the rubbing process, i.e., molecular reorientation occurs deeper within the layer. Experiments show that the penetration depth can be varied from less than 10 nm to more than 60 nm by variation in rubbing conditions. These findings are supported by surface second-harmonic-generation studies of LC monolayers deposited onto rubbed orienting layers and by infrared dichroism studies.

Preparation and characterization of highly oriented films of poly(di-n-hexylsilane)

It was found that rubbing as-cast films of poly(di-n-hexylsilane) (PDHS) with a wiping paper results in films withthe Si-backbone chains are oriented along the rubbing direction. The differences in the structure of the PDHS film before and after the rubbing treatment was investigated. In the oriented film of PDHS with a trans-planar conformation, the n-hexyl side chains stand almost perpendicular to the substrate surface. This rubbing method can also be applied to thin films of other polysilanes and polygermanes

Orientations of a Nematic Liquid Crystal in Sandwich-Type Cells Studied by Polarized Electronic Absorption Spectra

Abstract Polarized electronic absorption spectra of a nematic liquid crystal (4-butyl-4′-ethoxyazobenzene, BEAB) were measured in sandwich-type cells to which no rubbing treatment was applied. These polarized spectra were utilized to evaluate the mean squares of the direction cosines of the transition moment, those of the molecular orientation axis, and the three-dimensional absorption components as a function of the cell gap. It has been shown that the inclinations of the transition moment for the 354 nm band (long-axis polarized) and the molecular orientation axis to the cell plane increase with the decrease in the cell gap while the absorption component for the 354 nm band normal to the cell plane decreases. These observations provide a quantitative support for the molecular orientation model proposed previously that the molecular long axis tends to be oriented parallel to the cell plane in the interface region and perpendicular in the bulk region. The thickness of the interface region has been estimated to be about 0.02 μm by a model calculation based on a discrete model for the orientation of the BEAB molecules in the cell.

Quasi-epitaxial growth of diacetylene films by vacuum deposition

The quasi-epitaxial growth of vacuum-deposited films of diacetylenes on various substrates, including uniaxially aligned polymer surfaces formed with rubbing treatment or Langmuir–Blodgett technique, is reported. The oriented polydiacetylene (PDA) films are readily obtained from these monomer films using photopolymerization. Highly oriented PDA films with excellent optical qualities have been obtained on rubbed polyethylene terephthalate surfaces. The typical dichroic ratio of these oriented PDA films is more than 100:1. This ratio is high enough to permit the application of these films to optical waveguide devices. The method for obtaining these highly oriented PDA films is described in detail. In addition, the structure, the morphology, and the optical anisotropy of these PDA films is examined by x-ray and electron diffraction, electron microscopy, and other optical means.

Treatments of polypropylene fibres to optimize their reinforcing efficiency in cement composites

The effect of the geometry of polypropylene fibres and their surface treatment by chemical and physical means was studied to obtain cementitious composites with optimal flexural properties. Monofilaments of polypropylene were more efficient than split film or bundled multifilament strands. Acid, detergent and rubbing treatment of monofilaments were found to be particularly effective in enhancing the first crack stress and post-cracking behaviour of the composite. The influence of the various treatments was discussed in terms of the bonding nature as deduced by scanning electron microscope observations of the fibre-matrix interface.

The bistability of the surface-stabilized ferroelectric liquid-crystal effect in electrically reoriented chevron structures

Low-frequency electric field treatment irreversibly changes the chevron structure of a surface-stabilized ferroelectric liquid-crystal sample: the angle between the smectic layers and the surface normal decreases. As a result different textures appear, and a pronounced effect on the switching behavior is observed. The switching angle and the necessary pulse amplitudes at constant pulse width in order to obtain switching between both stable states have increased. The required reorientation voltages decrease with rising spontaneous polarization. This reorientation process is strongly influenced by the rubbing treatment of the alignment layer. The anchoring properties of the alignment layer seem to be directly responsible for the appearance of defects, for the initial switching angle, for the electric field strength necessary to reorient the chevron structure, and for the pulse amplitudes required to switch between both stable states.

Director orientation of a ferroelectric liquid crystal on substrates with rubbing treatment: The effect of surface anchoring strength

Abstract One of the most important problems with ferroelectric liquid crystals is obtaining homogeneous as well as bistable alignment, not only to study their physical characteristics but also for their application to optical devices. In this connection it was predicted that the formation of homogeneous alignment requires strong surface anchoring, whereas bistability requires weak anchoring. We have therefore developed a method to determine the surface anchoring strength, and have tried to clarify whether there is a suitable anchoring range. It was found that A/K 22 (A is the surface anchoring and K 22 is the twist elastic constant of liquid crystal) of 4 × 10−2 to 2 μm−1 satisfies the contradictory requirements for homogeneous as well as bistable alignments for the material studied, and the bookshelf structure is successfully formed with this condition.

Changes associated with experimental skin calcification. II. Changes of lipid, water content, and minerals during calcium accumulation.

The biochemical changes associated with skin calcification following xylene rubbing and lead acetate treatment were studied. There was an increase in the water content of the local area and a decrease in the total lipids. There was an early decrease in percentage ash with a subsequent increase from 6 h onwards. The lead content increased to a maximum at 24 h and decreased slowly thereafter, and no relationship was found between phospholipids and calcification. It is suggested that lead may initiate the calcification, but once cutaneous calcification has been initiated, it continues even after the lead concentration of the skin begins to fall.