Orientation film

Some cast (unoriented) polypropylene film is produced. Its clarity and heat sealabiUty make it ideal for textile packaging and overwrap. The use of copolymers with ethylene improves low temperature impact, which is the primary problem with unoriented PP film. Orientation improves the clarity and stiffness of polypropylene film, and dramatically increases low temperature impact strength. BOPP film, however, is not readily heat-sealed and so is coextmded or coated with resins with lower melting points than the polypropylene shrinkage temperature. These layers may also provide improved barrier properties. 

The examples in Figure 3 illustrate these possibilities. Figure 3a shows a diffraction pattern from a single crystal Fe thin film, oriented with the [001] crystal axis... 

Fig. 8. Dichroism of electronic absorption spectra of oriented and nonoriented PAN films after IR irradiation, (a) Dependence of optical density ( >) on the wavelength for various values of (angle between film orientation axis and light polarization plane).

Figure 9.4. The orientation of structural entities (rods) in space with respect to the (vertical) principal axis and the values of for, the uniaxial orientation parameter (Hermans orientation function) for (a) fiber orientation, (b) isotropy, (c) film orientation...

If the principal axes of the structural entities are all oriented in a plane perpendicular to the principal axis of the material (film orientation), the orientation parameter returns for = —0.5. 

Equatorial is a function g(tp), if its maximum is at 9 = n/2. Such distributions describe film orientation. 

Chemical solution deposition (CSD) procedures have been widely used for the production of both amorphous and crystalline thin films for more than 20 years.1 Both colloidal (particulate) and polymeric-based processes have been developed. Numerous advances have been demonstrated in understanding solution chemistry, film formation behavior, and for crystalline films, phase transformation mechanisms during thermal processing. Several excellent review articles regarding CSD have been published, and the reader is referred to Refs. 5-12 for additional information on the topic. Recently, modeling of phase transformation behavior for control of thin-film microstructure has also been considered, as manipulation of film orientation and microstructure for various applications has grown in interest.13-15... 

Researchers who have focused more on understanding cause-effect relationships in solution processing have given attention to film drying and pyrolysis behavior, densification processes, and nucleation and growth into the desired crystalline state. Both thermodynamic and kinetic factors associated with the phase transformation from the amorphous state to the crystalline state have been considered.11 119 Control of these factors can lead to improvements in the ability to influence the microstructure. It is noted that in the previous sentence, influence has been carefully chosen, since the ability to manipulate the factors that govern the nature of the phase transformation to the extent that full control of the microstructure is possible remains to be demonstrated. However, trends in characteristics such as film orientation and columnar versus uniaxial grains have certainly already been achieved.120... 

In addition to the role of the physical characteristics of the amorphous state on nucleation and growth, as indicated by Eq. 11, surface energies also play a role. The role of these properties on film orientation and microstruc-... 

Fig. 2 Schematic representation of control of block copolymer thin film orientations by adjusting polymer-substrate interactions neutral interfaces...

Fig. 3 Schematic representation of control over block copolymer thin film orientation by applying an electric field to orient PS-6-PMMA cylinders perpendicular to the substrate (taken from [43])...

Fig. 6 Schematic representation of controlling the block copolymer thin film orientations by using top-down lithography-defined chemically patterned heterogeneous sin-face...

Figure 5. ESR spectra of TEMPAMINE adsorbed on wet Na+-smectite films, oriented at 0° and 90° to the applied magnetic field.

Crystals growing on a substrate may be oriented every which way that is, the direction axes of individual crystallites can be randomly distributed. However, where one particular axis is oriented or fixed in nearly one direction, we speak about a single texture. When two axes are thus fixed or oriented, we speak about double texture. Monocrystalline orientation refers to a scenario in which there are three such nearly oriented axes, including epitaxial films. Orientation here is viewed with respect to any fixed (in space) frame of reference. Crystal planes and directions are illustrated in Figure 16.5. A brief discussion of the enumeration of these elements follows. 

When Lsub is kept constant and Dt is varied, similar selectivity in the film orientation is observed. Thin CuPc films prepared on amorphous substrates using PVD at Tsab = RT and low Dt (0.1 nm s ) are oriented with their (100) crystallographic planes preferentially parallel to the substrate surface (standing). At higher D (10 nm s ), an additional second type of preferred orientation is observed with (110) planes oriented preferentially parallel to the substrate surface (lying) (Resel et al, 2000). 

The piezoelectricity of polymer films and its inverse effect, strain induced by applied voltage, have been observed for as-cast films, oriented films, and films which has been polarized under a static field. It is at present believed that all kinds of polymer films exhibit more or less piezoelectricity. 

The different behavior (direct versus indirect band gap) of Si and Ge with respect to the film orientation can be explained in term of confinement effects on the conduction band minima (CBM) of the two semiconductors.Whereas the six equivalent ellipsoidal CBM of bulk Si occur in the (100) directions about 80% of the way to the zone boundary, in bulk Ge there are eight symmetry-related ellipsoids with long axes along the (111) directions centered on the midpoints of the hexagonal zone faces. Also the different confinement energy shifts with respect to the orientation of the layer can be interpreted in terms of the different highly anisotropic behavior of the effective masses for bulk Ge and Si [170,171]. 

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