STRUCTURE OF GELS 



69 



"dispersed" relatively to the other, for they both fill the available 

 space continuously. 



A gel of chain molecules is therefore not a two-phase system but a 

 single undivided phase. It is not only microscopically homogeneous 

 and optically empty, but also homogeneous from a physico-chemical 











I - 





\ 



^ / / 



\J 



b) 



Fig. 53. Gel framework, a) Projection, b) section across the frame- 

 work. Areas to be compared encircled. 



point of view. As in the case of real solutions, if small volumes are 

 considered, one always finds the same composition, with the sole 

 difference that the volumes contain only parts of chains instead of 

 whole molecules (Fig. 53b). Thus gels with a framework consisting 

 of individual chain molecules are one-phase systems. As in the case of 

 mesophases, this state deserves a nomenclature of its own. It will be 

 designated as pseudophase, especially in view of the fact that often not 

 all junction bonds are identical, so that the condition of homogeneity 

 is not strictly satisfied. 



In concentrated gels the chain molecules show a strong tendency 

 to orientate in parallel and to cluster in strands or rods. In such cases 

 the parallel arrangement may become so pronounced that here and 

 there the chain molecules combine to form a chain lattice. The length 

 of the crystal lattice in the direction of the chain axis need not be the 

 same as the length of these molecules ; the chains may protrude from 

 the end planes of the crystalline rods (Gerngross, Herrmann and co- 

 workers, 1930, 1932), continue further and eventually enter again into 

 another region of lattice order, as has been indicated schematically 

 in Fig. 54a. The more complete the average parallel arrangement of 

 the chains, the greater the probability of the occurrence of crystals 



