Uniaxially oriented film

Thus, the process of PAN transformation under the effect of IR radiation proceeds with considerable self-acceleration. The irradiation of uniaxially oriented PAN films gives a polymer with a distinct anisotropy of optical properties, dichroism in the visible spectral region in particular. Figure 8 presents dichroism curves [D =/(X)] at various angles (ip) between the polarization plane and the orientation axis. The same figure shows the dependence D =f(uniaxially oriented film. 

Uniaxially oriented films generally have high strength in only one direction, whereas biaxially oriented films are relatively strong in both machine direction (MD) and transverse direction (TD). Although intuitively one might expect biaxially oriented films to be preferred over uniaxially oriented films. 

In an uniaxially oriented film in which the c-axes of crystallites are oriented equally along the z- and — z-axes of the film (draw-axis) but the other two axes of the crystallites (a, b) are randomly oriented around the z-axis, the tensor related to the film coordinates is reduced to a simple form (Fukada and Yasuda, 1964),... 

For the growth of the above-mentioned uniaxially oriented films in ultra-high vacuum (UHV) an optimum deposition rate of several hundreds of pm/min was determined. For these conditions an increase in substrate temperature to around 373 K leads to the growth of crystalline films with crystal sizes above several pni a least up to thicknesses of 20 nm (Figure I3.7(b).(c)) [34]. The change in structure in comparison to oriented films can also be deduced from shifts and new splittings in the IR-spectra (Figure 13.8) and new peaks observed in X-ray diffraction measurements... 

From the point of view of applications, a6T is by far the most important oligothiophene (see Section 6). Like aST, sexithiophene forms highly ordered or crystalline films on oxidic surfaces, depending on the preparation conditions. The trend of forming films with higher crystallinity by increasing the substrate temperature is even more pronounced. On the other hand, there are no reports on completely closed uniaxially oriented films. 

The angular distribution of polarized components of fluorescence intensity of electrically or numerically oriented films of polypeptides show the pattern similar to those typical of the uniaxially oriented film. The degree of orientation of the films as expected from the contour of the pattern, is not so good despite the excellent orientation of the films, which may indicate that most of the fluorescent molecules are introduced into the gap regions that may possibly form amorphous regions. 

Plastic products with biaxial orientation (such as the wall of a PET carbonated drink bottle) have a greater resistance to puncturing than initially isotropic or uniaxially oriented film, because there is no weak direction in the plane of the film. In such anisotropic films, the value of cr — rr to cause thinning is larger than [Pg.245]

Oriented Films. Oriented multilayer films are prepared by stretching heated unoriented films. The film can be stretched in the direction coincident with the machine direction, or the direction perpendicular to the machine direction to obtain an uniaxially oriented film. A biaxially oriented film is stretched in both the machine direction and perpendicular to the machine direction. 

Uniaxially oriented films, Crystalline component = 11.8 (8) Mv = 3.8 X 10, reference Liquid-like component = 32.6 peak TMSi and solid adamantane 50 MHz,... 

Tajitsu, Y., Hosoya, R., Murayama, T. et oL (1999) Huge optical rotatory power of uniaxially oriented film of poly-L-lactic acid. Journal cf Materials Science Letters, 18,1785-1787. 

The sheet is then heated to about 95°C (above the glass transition point of approximately 70°C), where thermal mobility allows the material to be stretched to three or four times its original dimension in the MD. This uniaxially oriented film has stress-induced crystals whose main axes are aligned in the machine direction. The benzene rings, however, are aligned parallel to the surface of the film in the <1,0,0> crystal plane. The film is then again heated, generally to above 100°C, and stretched to three to four times its initial... 

The LSCEs represent a new class of macromolecular systems distinguished by macroscopically uniform anisotropy. The concept of LSCE can be furthermore extended to other synthesis routes and to the densely crosslinked systems. Macroscopic uniaxially oriented films can be formed by mechanical force, alignment surface [30], magnetic and electric fields [31], polarized light [32], etc., and then crosslinked to form an anisotropic network (LC network is abbreviated as LCN) if the mixture components contain polymerizable or crosslink-able bifunctional monomers (Figure 9.13). Alternatively, amorphous or liquid crystalline side-group and/or main-chain polymers incorporating additional... 

Stretch ratio n. In making uniaxially oriented films and filaments, the length of a sample of stretched film or filament divided by its length before stretching. 

Flat film and sheet extrusion produce uniaxially oriented film and sheet with improved clarity, better thickness uniformity, and a wide range of thicknesses. While the dies are very expensive and difficult to... 

The film (30y)used as the uniaxially oriented film was prepared by stretching 130y film cast from the melt using a metal roll at 107 C to a stretching ratio of 5.1, where the width remains almost constant. Although it has the highly oriented crystallites to a slight extent, the film behaves just as the uniaxially oriented film does.[12] The film provides the 30 -orientation when polarized. 

The q. -.(0) for the polarized and unpolarized films of the uniaxially oriented film is given in Figure 2-b. The unpolarized film has a slight amount of 90 - and 30 - orient-... 

Figure 2 BODF of (111) for various highly oriented films (a) 0 -oriented film, (b) unpolarized and polarized uniaxially oriented films, (c) unpolarized and polarized 90 -oriented films, (d) polarized 6Qo-oriented film.

Table 2 gives the 0 (111) values for various highly oriented films. The pola izing process produces about 28% of 30 orientation and d = 2.3 for the uniaxially oriented film. On the other hand, it produces about 43% of 30 orientation and d -=1.0 for the 90 -oriented film. Since the 30°-orienta-tion for the latter film is by far sharper than that for the former film, the orientation is not parallel to the piezoelectricity. 

The relationship between the piezoelectricity and the orientation of dipoles were investigated using the uniaxially oriented film. The film has the lowest highly orientation and the increase in the orientation can be easily seen. Now, an orientation parameter, 0 (b) is defined as the ratio of the amount of oriented crystallites to that of whole crystallites. ... 

Biaxial Orientation. Biaxial orientation substantially improves the physical properties of the film and increases its commercial value. Biaxially oriented films are produced by stretching polymers in directions perpendicular to each other in the melt or rubbery state. The improvement over uniaxially oriented films is due to the redistribution of c-axis chain orientation (36). This results in a film with enhanced physical properties in both directions. The direction perpendicular to the MD is defined as the transverse direction (TD). 

Property Biaxially oriented film Uniaxially oriented film... 

PHB can take up the helix conformation (called the a-form) or a planar zigzag conformation (called the p-form). The a-conformation results in lamellar crystals while the less common p-form is usually formed by extending the uniaxially oriented films of the PHB further, and occupies the amorphous regions between the lamellar crystals of the a-form. ... 

It should be noted that the properties of oriented films show considerable dependence on the processing conditions (e.g., biaxially oriented films are obtained by blow molding, while extrusion produces uniaxially oriented films). This is important because the mechanical properties of oriented specimens are considerably different in the flow and transverse directions of the films as shown hi Fig. 4.22 (measurements were done by a traditional tensile tester). When the film samples in the form of strips are prepared for TMA measurements, the strips should always be cut from the same orientation (Menczel et al. 1997). When preparing such samples, film widths of >2 mm are recommended in order to minimize edge effects. 

Films of C4.10 1,1-dialkyl substituted-co-MA copolymers have been orientated by stretching. Stretching could be achieved in one direction or in two mutually perpendicular directions in the plane of the film at 150-200°C and draw ratio of 8 1. Uniaxially oriented films have tensile break strength, in the orientation direction, of at least 10,000 Ib/in. Biaxially oriented films exhibited tensile strength in any direction in the plane of the film of at least 10,000 Ib/inl... 

Drawing products in their solid state (monofilament production, uniaxially oriented film, or biaxi-ally oriented film) maximizes molecular orientation and directional properties. In semicrystalline polymers drawing can lead to additional crystallinity development through alignment of the polymer molecules. The ability to successfully draw and process the polymer into oriented fibers, films, and profiles is often dependent on the quenching conditions used to form the precursor fiber, sheet, or profile. 

Bergman and co-workers (2-4] were the first to report measurements of the pyroelectric coefficient of PVDF. Ibey reported values of —2.4 X 10 C/m K for biaxidly oriented films (films stretched in two perpendicular directioos in the plane of the film during manufacture) and about -0.5 X 10 CVm K for uniaxially oriented films. 

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