Retardation films, types

The crosslinkable COCs have been suggested for the use as alternatives for a glass substrate of a liquid crystal display devices and an electroluminescence (EL) display devices. Moreover, a crosslinkable COC can be used as a polarizing film, surface protective film, retardation film, transparent conductive film, light diffusion film, film for EL display devices, transparent conductive composite material, anti-reflection film, etc. Methods how to prepare these types of films have been described in detail (47). 

This process can be nuclear or film type. In nuclear boiling, bubbles detach themselves quickly from the heat transfer surface. In film boiling the rate of heat transfer is retarded by an adherent vapor film through which heat supply must be by conduction. Either mode... 

As already mentioned (see Chapter 3), at the instant of foam formation the films and borders are in non-equilibrium state. The films thin mainly due to the capillary pressure, while the borders thin due to gravity or a pressure drop (when the foam is dried by the Foam Pressure Drop Technique [21-23]). The surfactant adsorption layers decrease the flow rate through the borders and films and the process of thinning becomes similar to the flow in thin gaps with solid surfaces. As indicated in Sections 3.2.1 and 5.3 the degree of retardation of the flow depends on the surfactant type and concentration as well as on the film type. A complete immobility at the film and border surfaces usually is not reached. 

This new type of temperature-compensating retarder film (TCR) is now commercially available. Its first applications have already shown that the temperature-dependent performance of displays for mobile applications can be considerably improved with only low additional costs. In this paper we report some results on the properties of these TCR films. 

Photoalignment can be applied to the fabrication of retardation films as well. Retardation films are used widely in LCDs for viewing angle enhancement as well as dispersion compensation. They can be made from uniaxial or biaxial materials. Within the class of uniaxial materials, many types of films can be made and they serve different functions. For example, for uniform films where the optical axis is fixed throughout the entire film, one can have A-plates, C-plates and O-plates as shown in Figure 5.8. 

In addition to retardation films where the optical axis is uniform, it is now possible to make retardation films with a variable optical axis. This is possible with developments in the synthesis of polymerizable LC materials or LC polymers. The photoalignment of all types of films will be discussed next. 

With the help of simple masks, photoalignment provides a means of patterning polarizers and phase retarders inside an LCD. It offers display designers much more freedom in optimizing the performance of the display. In addition to patterned polarizers and retardation films, photoalignment also allows different areas or subpixels to have different LCD modes. Many types of displays will become possible with the availability of such patterning of the pixels and subpixels. One... 

In tenns of an electrochemical treatment, passivation of a surface represents a significant deviation from ideal electrode behaviour. As mentioned above, for a metal immersed in an electrolyte, the conditions can be such as predicted by the Pourbaix diagram that fonnation of a second-phase film—usually an insoluble surface oxide film—is favoured compared with dissolution (solvation) of the oxidized anion. Depending on the quality of the oxide film, the fonnation of a surface layer can retard further dissolution and virtually stop it after some time. Such surface layers are called passive films. This type of film provides the comparably high chemical stability of many important constmction materials such as aluminium or stainless steels. 

Kinetic analysis with a Langmuir-type rate equation (Equation 13.4) [37] gave us the magnitudes of reaction rate constant (k) and retardation constant due to product naphthalene (K) for the superheated liquid film (0.30 g/1.0 mL) and the suspended states (0.30 g/3.0 mL) with the same Pt/C catalyst as summarized in Table 13.2. It is apparent that excellent performance with carbon-supported platinum nanoparticles in the superheated liquid-film state is realized in dehydrogenation catalysis on the basis of reaction rate and retardation constants. 

It has been speculated that there is a common origin of the reduced chemical etch rate for (111) oriented silicon substrates and for highly p-type doped substrates. But the electrochemical investigations discussed above indicate that the passivation of highly doped p-type Si can be ascribed to an oxide film already present at OCP, while no such oxide film is observed on (111) silicon below PP. This supports models that ascribe the reduced chemical etch rate on (111) planes to a retarded kinetic for Si surface atoms with three backbonds, present at (111) interfaces [Gil, A12], as discussed in Section 4.1. 

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