Orientation Measurements

It is relatively straightforward to detemiine the size and shape of the three- or two-dimensional unit cell of a periodic bulk or surface structure, respectively. This infonnation follows from the exit directions of diffracted beams relative to an incident beam, for a given crystal orientation measuring those exit angles detennines the unit cell quite easily. But no relative positions of atoms within the unit cell can be obtained in this maimer. To achieve that, one must measure intensities of diffracted beams and then computationally analyse those intensities in tenns of atomic positions. 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

Radially oriented measurements permit the analyst to understand the relationship of vibration levels generated by machine components where the forces are perpendicular to the shaft s centerline. 

Axially oriented measurements are used to determine the lateral movement of a machine s shaft or dynamic mass. These measurement points are oriented in-line or parallel with the shaft or direction of movement. 

Although it would be possible in principle to choose any set of orthogonal axes in the structural unit to define Ox,x2x3, it is implicit in the discussion of orientation in polymers that the structural unit also has at least orthorhombic symmetry (Point group D2) with regard to the development of orientation. As can be appreciated this can lead to an element of awkwardness in dealing with the results of orientation measurements, because the molecular situation is often more complicated. 

Figure 7 Relaxation of orientation measured simultaneously for both components in miscible PS/PVME blends following a rapid deformation (1 m/s) to a draw ratio of 2 at Tg +15°C. The time-resolved dichroic difference spectra were acquired using PM-IRLD. Reproduced with permission from Pellerin et al. [42]. Copyright 2000 American Chemical Society.

For orientation measurements, this tensor also needs to be expressed in the coordinate system OXYZ, axrz, using the matrix transformation u.xyz = Oaxyz / where O is a matrix whose elements are the direction cosines of the coordinate axes and is its transposed matrix [44]. 

The theory of orientation measurements by linearly polarized Raman spectroscopy has been developed in detail by Bower in 1972 [44]. The Raman intensity, I, is given by... 

As seen in this chapter, the theory and procedures for orientation measurements are well established, including for quantitative characterization. These methods can provide very accurate and useful information in the fields of synthetic, natural, and bio-inspired macromolecules. To this aim, researchers can make use of a wide range of techniques, each having its advantages and limitations. As judged from the recent literature, the studies devoted to the quantification and characterization of molecular orientation still represent a very dynamic research field and advances still continue to emerge. Further progresses in the development of new methods and new techniques to characterize orientational order are thus expected in the future. 

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A good applications-oriented measure of the use temperature for a ma-teral is the heat distortion or heat deflection test (HDT). The HDT is described by ASTM-D648 as the temperature at which a sample of defined dimensions (5 X Vi X Vs (or Va) in.) deflects under a flexural load of 66 or 264 psi placed at its center. In case of a largely amorphous polymer, the HDT temperature is typically slightly (10 to 20 °C) lower than the Tg as determined by DSC or DTA, whereas with more-crystalline polymers, it more closely correlates with the Tm. The HDT temperature is a useful indicator of the temperature limits for structural (load-supporting) applications. A loaded cantilever beam is used in another heat deflection test called the Martens method. 

We have done most of our studies on granular PTFE by compacting it into a preform and sintering to make a shape matching ASTM D-1708-66 for tensile testing. Orientation measurements by IR dichroism require thinner specimens, and for this purpose we used dispersion-grade material, commercially cast and processed into film (Dilectrix Corp., Farmingdale, NY). These films were used as received without further heat treatment. ... 

ORIENTATION MEASURED FROM INVERSE POLE FIGURES... 

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Figure 13.1 Examples of the field dependence of piezoelectric coefficients (a) direct effect in ferroelectric ceramics, measured with a dynamic press (b) converse effect in rhombohedral 60/40 pzt thin films with different orientations, measured with an optical interferometer [1], correspond to pseudocubic axes.

Figure 11 Final rotational state distributions for NO scattered from Ag(l 11) for different initial orientations measured at a final angle of 70° and at an incidence angle of 35°. The upper panel corresponds to NO initially oriented with the N-end towards the surface and shows approximately a Maxwell-Boltzmann distribution as given by the dotted line. The lower panel corresponds to NO initially oriented with the O-end towards the surface and shows a pronounced rotational rainbow. From Geuzebroek et al. [36],...

FIG. 13.100 The sonic compliance versus the orientation measured by X-ray diffraction during extension of a low-modulus PpPTA fibre. From Northolt and Baltussen (2002). Courtesy John Wiley Sons, Inc. 

Recently, the orientation behavior of poly-(IV-5) was compared to both poly-(IV-4) and a statistical copolymer poly-IV-5-COEN (COEN=cyclooctene) [51]. The experiments shotved that, compared to poly-(IV-5), samples of poly-(IV-5-COEN) were easier to orientate, a finding that was attributed to the more flexible chain. The dependence of the magnetic field and the temperature on the degree of orientation, measured by the birefringence and the optical transparency, is shown in Fig. 6. 

Lipid A was investigated by FTIR, X-ray diffraction, and fluorescence techniques (Naumann et al., 1987). Analysis of the CH2 scissoring vibrations showed that lamellar structures exist at temperatures below 30 °C, but that no stable closed vesicles are formed. Orientation measurements of lipopolysaccharides prepared from E. coli and Salmonella minnesota by ATR-FTIR also showed a highly ordered gel phase. Besides, the transition from the gel pha.se a to the liquid crystalline phase was also studied (Brandenburg and Seydel, 1988). 

In this chapter, the results of orientation measurements by infrared dichroism will be presented, discussing three main topics ... 

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