Polymer orientation ratio

Problems related to the use of a guest dye can be reduced if the polymer contains a fluorescent chemical group. Gohil and Salem [70] took advantage of such intrinsic fluorescence to characterize the in-plane distribution of orientation in biaxially drawn PET films. In these experiments, the chain-intrinsic fluorescent label is due to the formation of dimers by two terephthalic moieties, exclusively within the noncrystalline regions. A comparison between sequential and simultaneous drawing along the MD and TD directions was undertaken for a fixed MD draw ratio of 3.5 and various TD draw ratios. The orientational order was characterized by two "orientation ratios" Rmd and RTD such that... 

Hot-Drawn ABS Polymer. Draw ratios were varied between 1.0 and 2.9. In order to determine the extent of orientation produced during drawing, specimens were sectioned and etched the shapes of the initially spherical rubber particles are a measure of orientation (8). In general, the effective draw ratios calculated from particle shapes were close to the actual draw ratios. 

Material Polymer Draw ratio Mode of Testing Geometry Orientation Band angle Deformation Simple Pure shear shear y e Optical Reorientation Predicted from eqn, (11) Measured a° a° ... 

Another standard method of measuring polymer orientation is infrared dichroism, which refers to the ratio of the IR absorption for light having... 

The purpose of this section is not only to confirm the identification, but also to characterize certain polymers and polymer types in detail. Although methods to determine microstructures and impurities, such as chemical inversions, modifications, and multiple bond formations, are different from polymer to polymer and are discussed separately, the methods used for the determination of density and crystallinity, as well as polymer orientation, are common to most polymers. Thus, the determination of crystallinity and density will be covered in this section, in Sec. 3.1, and likewise, the orientation of the polymer chain will be described in Sec. 3.2. The use of absorption coefficients to calculate properties, such as crystallinity, doublebond content, chain branching, and monomer ratios, is described in reference texts [14,15]. Today most work is performed by Fourier transform infrared (FTIR), and so an attempt has been made to feature coefficients from the latest reference sources, which include data acquired by FTIR. 

Polarized FTIR spectroscopy has been used extensively to study polymer orientation (i.e., the dichroic ratio and dichroic difference are normally obtained from spectra recorded sequentially with the infrared radiation polarized parallel and perpendicular to a reference direction). To improve the sensitivity of this technique, and to follow accurately the dynamics of orientation, FTIR spectroscopy has been coupled with a polarization modulation (PM) technique whereby the dichroic difference spectrum is recorded directly, thus minimizing instrumental and sample fluctuations (this is discussed later in the chapter). 

Polymers oriented by drawing are of considerable practical importance because they can display up to 50% of the theoretical chain direction modulus of the crystals. This short-fall in modulus is caused by imperfections within the crystals and the presence of folds and non-crystalline material. The value of modulus obtained depends principally upon the crystal structure of the polymer and the extent to which a sample is drawn (i.e. the draw ratio). The maximum draw ratio that can be obtained in turn... 

We have described the orientation of poly[2,7-(9,9-dioctyl)fluorene] on top of a rubbed poly(l,4-phenylenevinylene) (PPV) layer (Fig. 7.7) [33, 34]. Since PPV is a conjugated polymer itself the problems with the extremely good insulator polyimide, which is not well suited as a hole transport layer in OLEDs, are not present in such PLEDs. With an OLED setup consisting of ITO, a 30 nm thick rubbed PPV orientation layer, an annealed 70 nm PFO layer and a calcium top electrode we obtained blue electroluminescence with an orientation ratio of 25 1 parallel and perpendicular to the rubbing direction of the PPV. If a polythiophene... 

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