Phase Transition in Gaussian Networks

As was pointed out in Section II-4, a gel, swollen originally to a degree qc, which is less than the maximum swelling, may become incompatible with the diluent if the network parameters v, or q0 change. The activity of the diluent in the original, partially swollen gel is less than the activity of pure diluent. If the network parameters change in such a way that they decrease the maximum swelling of the 

Passing this point, excess diluent is separated outside the network phase 49). The development of two phases is called (macro)syneresis. 

Conditions (III-37) and (III-38) can be rewritten in terms of Eq (III-21a) for the range of uniform segment concentration and volume-independence of the reference state  

The Gaussian network theory can, therefore, predict phase separation in partially swollen systems. Phase separation can be induced by increasing the degree of crosslinking or increasing the interaction parameter %. Examples are given in Fig. 16. 

One has to bear in mind the importance of the parameter q0 which is proportional to qe, but which may change also with the crosslinking density, according to relation (III-19). Eq. (III-39) can then be rewritten as 

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