Uniaxially drawn film

FIGURE 5.5 Polarized PL from a gel-processed, uniaxially drawn film of EHO-OPPE (cf. Figure 5.4) in UHMW-PE. Twisted tapes (drawn to a draw ratio A = 80) are shown under excitation with UV light (365 nm) and the pictures were taken through a linear polarizer with its polarization axis oriented horizontally (a) and vertically (b). (After Weder, C., Sarwa, C., Bastiaansen, C., and Smith, P., Adv. 

Fibers are commercially made from uniaxially drawn film. The film is extruded, slit into tapelike strips, drawn, fibrillated, and wound. As in the case of spinning, the drawing produces preferred alignment of the polymer chains along the axis of pull. If the drawing precedes slitting, the fiber gives some cross orientation and is less apt to split. 

Polymers which have been found to exhibit intrinsic piezoelectricity for a uniaxially drawn film are, beside polypeptides, polypropylene oxide) (PPO) (Furukawa and Fukada, 1969), cellulose (wood) and its derivatives (Fukada, 1970), board paper and polyethylene terephthalate) (PET) (Wada and others, 1966). These films have an anisotropic piezoelectricity as defined by Eq. (61). 

In order to clarify the intrinsic crystal piezoelectricity, it is very important to know how form I crystallites deform when strain is applied. The relationship between the external strain and the lattice strain for the uniaxially drawn film is shown in Figure 5, where (A) and (B) denote samples annealed at 175 C and 120°C for 2hr, respectively. The c axis strain of samples is as small as 0.8-1.5% of the external strain, as deduced from the large elastic constant along c axis. On the other hand, the a and b axes strains are very large (2.5-6.0%. The apparent Poisson s ratio of the form I crystallite is extremly large, which depends on the conditions of anealing = 4.0 (120 C)... 

Poled PVDF films show fenoelectiic behavior clearly demonstrating the polarization reversal in the dielectric Itysteresis curve (Nalwa 1995). Locally created domains ate reported (Giithner and Dransfeld 1992) in scanning force microscopy observations in PVDF. Typical values of the spontaneous polarization are 8-10 X 10 Ccm and of the coercive field 50-100 kVmm . For the material properties see Table 7.17. Uniaxially drawn films are much mote anisotropic in piezoelectric properties. The piezoelectric coefficients are higher than e.g. for quartz crystals, but lower than for PZT ceramics. It is highly desirable to improve the piezoelectric coefficients for the possible applications of polymers. 

A fibre or a uniaxially drawn film will usually show no preferred orientation in the plane normal to the fibre axis or the draw direction (see Figure 7.2). The compliance matrix then reduces to a form with only five independent constants ... 

Everall [66] used confocal Raman microspectroscopy on uniaxially drawn films of PET to determine 200- He noted that several corrections needed to be made due to the... 

Studies of mechanical anisotropy in polymers have for the most part been restricted to drawn fibres and uniaxially drawn films, both of which show isotropy in a plane perpendicular to the direction of drawing. The number of independent elastic constants is reduced to five [3, p. 138]. Choosing the 3 direction as the axis of symmetry, the compliance matrix sy reduces to... 

In the dynamic transmission mode, information about two-dimensional dynamic dichroic differences can be attained [46]. It is useful to study uniaxially oriented polymers such as strongly elongated fibres. However, the orientation of most polymer films should be considered biaxial, even with uniaxially drawn films, which still show slight biaxial orientation at the surface [52]. This fact suggests that the two-dimensional dynamic dichroic data obtained from transmission mode is not necessarily adequate for evaluating most (biaxially oriented) polymer films. 

Kaito A, Li Y, Shimomura M, Nojima S. Oriented lamellar structures in uniaxially drawn films of poly(vinylidene fluoride) and poly(3-hydroxybutyrate) blends studied by small-angle X-ray scattering measurements. J Polym Sci B 2009 47 381-392. 

Fig. 4. Pore radius distribution of uniaxial drawn film from PP with draw ratio of 3 (a) and 8 (b)...

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