no FUNDAMENTALS OF SUBMICROSCOPIC MORPHOLOGY I 



The swelling medium penetrating between the string4ike structural 

 elements causes the system to inflate laterally. For this reason swelling 

 is always at its greatest in directions perpendicular to the direction 

 of orientation of the micellar texture, and is almost zero along the 

 fibre axis if the fibre texture is ideal. The arrangement of the micellar 

 strands can therefore be derived from the anisotropy of swelling, or 

 conversely, the anisotropy of swelling or shrinking to be expected can 

 be computed from the optical anisotropy measured (Steinbrinck, 

 1906; Ziegenspeck, 1938). 



If it is assumed that the microfibrils of native fibres, made up of 

 polyhedral micellar strands, possess a more or less circular cross- 

 section (Fig. 74b, p. 105), these can be idealized as circular cylinders. 

 It is then found that in the completely dry state 9.5 per cent, by vol. of 

 intermicellar empty spaces must occur between the strands (Hermans, 

 1938). This value tallies approximately with the average empty space 

 (8.5 %) obtained from determinations of double refraction and density 

 (Frey-Wyssling and Speich, 1942), showing that in well-dried 

 fibres the microfibrils are fairly closely packed. Gels in which the 

 colloid portion is crystalHzed imperfectly, so that a large amount of 

 amorphous substance is present, swell much more than well-crystallized 

 fibres, the swelling medium being able to penetrate into the unordered 

 regions, causing them to swell. Nevertheless it does not succeed in 

 solvating the individual chain molecules in the ordered regions. 



Intramicellar swelling. If, however, the affinity between the swelling 

 medium and the chain molecules is stronger than the binding forces 

 in the chain lattice, the swelling medium will penetrate into the lattice 

 and widen it. This widening can be followed by means of X-rays and 

 is often found to abolish the interferences. In that case the chain 

 molecules are completely solvated and if they are not kept together by 

 valence bridges (p. 67), unlimited swelling can take place which will 

 gradually lead to the dissolved state of a sol. 



In many cases, however, swelling media react with the side groups 

 of the macromolecules, causing a change in the chemical character 

 of the high polymer chains. This applies, for instance, to the esterifica- 

 tion of solid cellulose (nitration, acetylation, Frey-Wyssling, i936d). 

 If the changed chain molecules cannot be solvated by the penetrating 

 swelling medium, the result is a lattice of the newly formed substance 

 and no unlimited widening of the chain lattice takes place. This 



