68 FUNDAMENTALS OF SUBMIC ROSCOPIC MORPHOLOGY 



CH=CH2 



CH=CH! 



Divinyl- 



benzene 



-CH2—CH-CH2- CH - -CH2-CH 



-CH2—CH-CH2-CH — CH2-CH 



-CH2-CH-CH2- 



■CH2-CH-CH2- 



■CH2-CH-CH2- 



-CH2-CH-CH2— 



Fig. 52. Limited swelling of polystyrene 

 (from Staudinger, 1936a). 



of methylcellulose can be interlinked by dicarbon acids (Tavel, 1939) 

 or chains of polygalacturonic acid (pectic acid) by epioxides (Deuel, 

 1947a). When main valency bonds occur between the chain molecules, 

 even the most suitable solvating medium is no longer capable of 

 destroying the gel structure. Notwithstanding considerable swelling 



(e.g., a 30-fold increase 

 in volume) the frame- 

 work of the chains is 

 0^ ^^ preserved. It is possible 



[] that cellulose also con- 



V _ _ tains a few of such main 



valency bridges (see, for 

 instance, Lieser, 1940; 

 Meyer, 1940a; Pacsu, 

 1948). These would li- 

 mit the swelling and 

 would have to be de- 

 graded chemically when cellulose is dissolved in cuprammonium. 

 It can be said in general that limited swelling occurs when certain 

 junctions of the gel frame (cohesive or main valency bonds) cannot 

 be loosened. 



Concept of phase in gels. In the case of a sol one can (if necessary) 

 speak of a "dispersed phase" distributed in a dispersing medium, 

 although difficulties arise which have already been mentioned on p. 

 16. With sols containing chain molecules instead of colloid particles 

 in the sense of the classical theory of dispersoids, to uphold the con- 

 cept "phase" is decidedly wrong. For, according to the definitions in 

 phase theory, separate molecules may not be characterized as phases. 

 With gels the conditions are much the same. In a chain framework, 

 it is incorrect to speak of a "dispersed phase", because regions with 

 a thickness of molecular dimensions are not homogeneous phases, 

 and the concept "dispersing medium" also becomes questionable. 

 Consider a gel consisting of equal percentages of chains and water; 

 a projection of the structure then gives the impression that the water 

 is distributed as a "dispersoid" in closed compartments (Fig. 53a) 

 whereas, conversely, in a cross-section of the gel the sections across 

 the chain molecules appear as "dispersed" particles distributed in the 

 liquid (Fig. 5 3b). In reality, however, neither of the two partners is 



