Stretched polymer film

Q are the absorbance and wavenumber, respectively, at the peak (center) of the band, p is the wavenumber, and y is the half width of the band at half height. Liquid band positions ate usually shifted slightly downward from vapor positions. Both band positions and widths of solute spectra are affected by solute—solvent interactions. Spectra of soHd-phase samples are similar to those of Hquids, but intermolecular interactions in soHds can be nonisotropic. In spectra of crystalline samples, vibrational bands tend to be sharper and may spHt in two, and new bands may also appear. If polarized infrared radiation is used, both crystalline samples and stressed amorphous samples (such as a stretched polymer film) show directional effects (28,29). 

The parameters K1/ K2/ and K3 are defined by the refractive indices of the crystal and sample and by the incidence angle [32]. If the sample has uniaxial symmetry, only two polarized spectra are necessary to characterize the orientation. If the optical axis is along the plane of the sample, such as for stretched polymer films, only the two s-polarized spectra are needed to determine kz and kx. These are then used to calculate a dichroic ratio or a P2) value with Equation (25) (replacing absorbance with absorption index). In contrast, a uniaxial sample with its optical axis perpendicular to the crystal surface requires the acquisition of spectra with both p- and s-polarizations, but the Z- and X-axes are now equivalent. This approach was used, through dichroic ratio measurements, to monitor the orientation of polymer chains at various depths during the drying of latex [33]. This type of symmetry is often encountered in non-polymeric samples, for instance, in ultrathin films of lipids or self-assembled monolayers. 

The polarization direction of an electronic transition may be determined by measurement of the absorption of polarized light by aligned molecules. (Cf. Michl and Thulstrup, 1986.) Orientation may be achieved in a number of ways. When single crystals are used or when the molecules of interest are incorporated into appropriate single crystals, a very high degree of orientation can be obtained if the crystal structure is favorable. Other methods accomplish orientation by embedding the molecules in stretched polymer films (polyethylene, PVA Thulstrup et al., 1970) or in liquid crystals further possibilities are orientation by an electric field (Liptay, 1963), or, in the case of polymers such as DNA, by a flow field (Erikson et al., 1985). 

When an oriented sample is available, such as a drawn fibre, a stretched polymer film, or an anisotropic liquid crystal [1-5, 12, 41-50], it is possible to measure the orientation of the labelled C— H bond vector with respect to the sample axis. When local orientational constraints are collected for several connected groups in a polymer, they can be combined to calculate... 

INDO methods. Dipole moments of states as a function of twist around bonds are examined and predictions made of photoisomerization effects. Energies, dipoles, and non-adiabatic couplings have also been computed for diradical and zwitterion states of ethylene and propene. Conformational analysis of flexible trans-dienes can be made by the technique of polarization spectroscopy in stretched polymer films as has already been mentioned. Vitamin D and its derivative have been selected as examples of the use of the technique. 

In the gas phase or in isotropic hosts, such as liquids, polymers or glasses, the transition dipole moments of the guest molecules exhibit random orientations. In anisotropic systems, like crystals and stretched polymer films, there is usually a correlation between the orientation of the molecule and the geometry of the host matrix. The probability of electric dipole absorption depends on the square of the scalar product... 

Stretched polymer film Attach a stretched polymer film to the substrate. [4]... 

Thus for reasonable performance polarizers, the dichroic ratio has to be over 25. Current polarizers are based on iodine impregnation of stretched polymer films [4] (e.g. 30-50 tim polyvinyl alcohol). The dichroic ratio is over 50. There are two issues in getting high performance from polarizers based on anisotropic absorption. First, the intrinsic absorption anisotropy has to be large. Second, the absorber has to be well aligned in one direction. Both are difficult issues. 

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