Intensity functions equatorial section

Fig. 16. (a) Experimental intensity function for the oriented random copolymer X. The orientation was introduced by melt extrusion, (b) Equatorial (-------------------) and meridional (--) sections of (a). 

Fig. 20. The equatorial cr=90 section (dashed line) and the meridional a=0° section (full line) of the intensity function of Fig. 19.

Figure 8.37. Equatorial streak analysis of a poly(ether ester) during straining as a function of elongation, . (a) Intensity projected on the cross-sectional plane (b) 2D CLD computed from the projected intensity... 

Early powder diffraction experiments relied mostly on the Debye-Scherrer experiment to record a diffractogram. A broad film strip set into a cylindrical chamber produced the first known two-dimensional powder diffraction data. In contrast to modern methods the thin equatorial strip was the only part of interest and intensities merely optically and qualitatively analysed. This changed drastically with the use of electronic scintillation counters. Intensities were no longer a matter of quality but quantity. Inevitably the introduction of intensity correction functions long known to the single-crystal metier, i.e. Lorentz and polarization corrections (see Section 14.3), made their way into the field of powder diffraction. 

The equatorial spots are extended in the vertical direction and have the form of arcs the intensity decreases with increasing i -angle as shown in Fig. 5.21b. This is a result of a non-ideal orientational order the higher the order parameter S, the shorter the arcs. From the diffractogram one can find the distribution of intensity and calculate S [7]. In some cases, even the orientational distribution function for molecules /(i ) can be calculated from experimental data as schematically shown in Fig. 5.22. Generally, the shape of the function is determined by different Legendre polynomials P2(cosi ), P4(cosi ), etc. (see Section 3.3) and, in principle, different order parameters P2, P4 etc. can be found from experiment. 

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