Thin film retarder

Figure 9.18 shows the process steps for the fabrication of a thin film retarder. A solution of a mixture of the reactive LC monomers doped with... 

Fig. 9.19. (left) A schematic of the molecular order of the reactive LC molecules in a coated thin film retarder. The order is forced to be planar by the rubbed poly-imide. (right) An image of a uniaxial planar wet-coated retarder viewed in between two crossed polarisers and its orientation with respect to the crossed polarisers. (A) Analyser, (P) polariser, and (R) retarder. 

Fig. 9.18a—c. Schematic representation of the manufacturing process of coated thin film retarders. 

Foams are thermodynamically unstable. To understand how defoamers operate, the various mechanisms that enable foams to persist must first be examined. There are four main explanations for foam stabiUty (/) surface elasticity (2) viscous drainage retardation effects (J) reduced gas diffusion between bubbles and (4) other thin-film stabilization effects from the iateraction of the opposite surfaces of the films. 

If the gas diffusion between bubbles is reduced, the collapse of the bubbles is delayed by retarding the bubble size changes and the resulting mechanical stresses. Therefore single films can persist longer than the corresponding foams. However, this effect is of minor importance in practical situations. Electric effects, such as double layers, form opposite surfaces of importance only for extremely thin films (less than 10 nm). In particular, they occur with ionic surfactants. 

The fraction of octahedrally coordinated aluminium species is much larger in thermally treated aluminophosphate mesoporous thin films than in thermally treated powders. The difference between thin films and powders might be due to a substrate effect that could retard the formation of a well-defined aluminophosphate framework. Indeed, it has been... 

Low levels of potassium iodide strongly retard the thermal decomposition of thin films of cellulose nitrate. 

Polyphosphinoboranes are of interest with respect to their potentially useful physical properties such as flame-retardant behaviour and an ability to function as precursors to BP-based ceramics. In addition, the electron-beam sensitivity of some polyphosphinoboranes has been demonstrated. This allows their use as lithographic resists for patterning applications when coated as thin films on substrates such as silicon (Figure 9.11). ... 

A high bulk liquid viscosity simply retards the rate of foam collapse. High surface viscosity, however, involves strong retardation of bulk liquid flow close to the surfaces and, consequently, the drainage of thick films is considerably more rapid than that of thin films, which facilitates the attainment of a uniform film thickness. 

Van der Waals forces The case pex = 0 is purely academic, since van der Waals interactions are omnipresent and are known to affect the stability of thin films. In the non-retarded case, the van der Waals disjoining pressure is... 

Structurally modified PVF has been extruded.66 Thin films are manufactured by extrusion of a dispersion of PVF in a latent solvent.67 Such dispersion contains usually pigments, stabilizers, plasticizers, and flame retardants as well as deglossing agents if needed. The solvent is removed by evaporation. The extruded film can be biaxially oriented and the solvent is removed by evaporation only after the orientation is completed. 

Van der Waals interactions (continued), retardation 1.4.6c In thin films 1.101... 

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