X-RAY DIFFRACTION 



of a certain degree of orientation is indicated. Quantitatively one can 

 measure the length of each individual segment, parallel to the circum- 

 ference of the ring to which it belongs, and convert this length into the 

 angular opening of the segment. This angular opening describes the 

 degree of orientation in the investigated material: if it is large, the 

 crystallites scatter widely about certain directions and the orientation 

 is poor; if, however, the angles corresponding to all segments in the 

 diagram are small, i. e., the diagram consists of sharp spots rather than 

 smeared out segments, then the orientation of the crystalline domains 

 in the sample is good. In general, orientation of the crystallites is 

 closely connected with important mechanical properties such as 

 strength, rigidity, or toughness. 



The last feature of a protein fiber x-ray pattern, which deserves 

 quantitative consideration is the general background of diffusely scat- 

 tered intensity. This indicates that, in addition to the well-ordered 

 fraction producing the comparatively sharp diffraction lines and spots, 

 a certain amount of material exists which is in a disordered state and which 

 cannot produce any characteristic diffraction phenomenon. This 

 amorphous or disordered matrix in which the crystalline areas are em- 

 bedded is mainly responsible for the resilience, flexibility, and swelling 

 properties of a protein fiber and hence may represent a very valuable 

 constituent of it. In principle, it would be possible to carry out a 

 measurement of the integrated intensity of this diffuse scattering and by 

 comparing it with the total intensity of the crystalline pattern to arrive 

 at a quantitative figure of the ratio of crystalline to amorphous material. 

 In practice, however, it is possible to obtain this ratio only as an esti- 

 mate rather than as a precise measurement. One can, for example, 

 find out whether a certain treatment of a sample has increased or de- 

 creased its degree of crystallinity. In general, procedures such as 

 stretching, rolling, drawing, deswelling, etc., increase the degree of 

 crystallinity, while all steps of relaxation and swelling tend to increase 

 the disorder in the material. Since the ratio between ordered and dis- 

 ordered constituents is of great importance for the mechanical and col- 

 loidal properties, even an approximate estimate of it can contribute to 

 an understanding of the behavior of certain systems. 



Until recently, comparatively primitive x-ray diffraction tech- 

 niques were used to study proteins — primitive in the sense that they 

 were not the most advanced available at the time of the experiments in 



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