Crystals and Liquid Crystal Displays LCDs

Liquid Crystals and Liquid Crystal Displays (LCDs) 

In order to understand the basic principles of operation of the many different kinds of LCDs being developed and/or manufactured at the present time, it is necessary to briefly describe the liquid crystalline state and then define the physical properties of direct relevance to LCDs. First, the nematic, smectic and columnar liquid crystalline states will be described briefly. However, the rest of the monograph dealing with liquid crystals will concentrate on nematic liquid crystals and their physical properties, since the vast majority of LCDs manufactured operate using mixtures of thermotropic, non-amphiphilic rodlike organic compounds in the nematic state. 

The direction of the director is random in space and time. However, the director 

Schematic representation of the Dho columnar phase with an ordered hexagonal arrangement of the columns of disc-shaped molecules with a regular period of the discs within the columns. The director is parallel to the columns and normal to the plane of the discs. 

Calamitic compounds which exhibit a smectic and/or nematic phase usually consist of a relatively rigid central core containing co-linear six-membered rings, either aromatic rings, such as 1,4-disubstituted-phenylene, 2,5-disubstituted-pyridine, 2,5-disubstituted-pyrimidine, 3,6-disubstituted-pyridazine, and alicyc-lic rings, such as /ra j-l,4-disubstituted-cyclohexane, 1,4-disubstituted-bicy-clo[2.2.2]octane, 2,5-disubstituted-dioxane. Heteroaromatic rings tend to lead to the formation of smectic phases rather than the nematic phase unless combined with a polar terminal function, such as a cyano group. The dependence of the liquid crystalline transition temperatures on the nature of 

---

We are all familiar with tire tliree states of matter gases, liquids and solids. In tire 19tli century the liquid crystal state was discovered [1 and 2] tliis can be considered as tire fourtli state of matter [3].The essential features and properties of liquid crystal phases and tlieir relation to molecular stmcture are discussed here. Liquid crystals are encountered in liquid crystal displays (LCDs) in digital watches and otlier electronic equipment. Such applications are also considered later in tliis section. Surfactants and lipids fonn various types of liquid crystal phase but this is discussed in section C2.3. This section focuses on low-molecular-weight liquid crystals, polymer liquid crystals being discussed in tire previous section. 

Liquid Crystal Displays (LCD). Liquid crystal displays, once limited to small devices such as calculators, are now displacing color CRT (cathode ray tube) displays in commercial quantities. The ability to fabricate these display devices at high quality and at low cost is partially due to the wider spread use of photopolymer-based materials. Photopolymer technology is being used for the alignment of liquid crystal (LC) elements (49), the orientation of ferroelectric materials (50), the synthesis of LC polymers (57) and the manufacture of color filters for liquid crystal display applications (52). 

In a liquid-crystal display (LCD) device, the two electrodes are parallel and separated by a thin layer of liquid crystal (see Figure 2.2). The liquid crystals in this layer naturally adopt a helical structure. 

G.3.3.3 Liquid Crystal Displays (LCDs). Liquid crystalline polymers, first intro-dnced in Section 1.3.6.3, are ntilized for a different type of computer and television display, the liquid crystal display (LCD). Most of today s laptop computers and handheld devices ntilize color flat panel displays where the light transmission from the... 

Afterwards there appeared what has become the main application liquid crystal displays (LCDs) based on the twisted nematic (TN) mode. These are commonly used for flat panel displays (e.g., desk calculators). Thin film transistor (TFT) LCDs enabled a large number of segments (e.g., 640 x 1024) to be used and they had advantages like... 

The widespread use of liquid crystals for displays in digital watches, pocket calculators, and computer screens hinges on the fact that the orientation of liquid-crystal molecules is extremely sensitive to the presence of small electric fields and to the nature of nearby surfaces. As shown schematically in Figure 10.31, a typical liquid-crystal display (LCD) contains a thin layer of nematic liquid-crystal molecules sandwiched between two glass sheets that have been rubbed in different directions with a thin nylon brush and then layered with tiny transparent electrode strips made of indium/tin oxide. The outside of each glass sheet is coated... 

Modern communication operates independently of time of day or geographical location. It brings people closer, makes life easier, and has changed the working environment profoundly. At the heart of all this sits a product so common that most people do not even think about its presence. Liquid crystals (LCs) are hi-tech chemical materials with unique properties. Without them we would not have Liquid Crystal Displays (LCDs) - lightweight, flat displays that consume little energy. 

A "PC projection panel" and overhead projection of the spreadsheet greatly eases viewing of the computer video output. The PC projection panel provides an overhead projection of the computer screen so that all review team members can easily and simultaneous observe and comment on the recorded information as it is being recorded. The PC projection panel consist of a liquid crystal display (LCD) panel that duplicates data, text or graphics, generated from the computer screen. When placed on an overhead projector the LCD image is projected onto a projector screen or a wall. Personal computer screens are viewable by only two or three personnel at a time. A typical review involves at least 5 personnel, so the PC projection pad enables all participants to view the software worksheet as it is prepared (note a "reflective" type of overhead projector will not operate with the PC projection panel, direct illumination from below the panel is required). Further details of a typical PC projection panel are provided in Appendix F. 

---