Polyelectrolytes: Theory, Properties and Applications

8 F. Benmouna, R. Kaci and M. Benmouna

In this case, the bare structure factors read

       

   

0 0 0

a b 1/ 2 ab T 1/ 2

22

0 T 1/ 2 T

; 2 ;

44

.

4

NN

S q S q P S q P P

N

S q P P P



   



  

(12)

Another simplification comes from the lack of preferential affinity of
solvent towards A or B monomers (i.e; as = bs = ps). Here, Saa(q) can be
written as a sum of two terms

   

 

aa T 1/ 2 T

ab ab 1/ 2 T

ps T

121 1

4 12 2

Sq P PP

NNPP

NP



  

    





. (13)

This equation expresses the interplay between polymer/solvent interaction and

the intra chain incompatibility. The former is driven by the parameter ps

inducing macrophase separation, while the latter is due to ab responsible for

microphase separation. The first term on the right hand side (RHS) of Eq. 13

gives the contribution of the chain as a whole feeling solvent interaction ps

augmented by the quantity ab/2. Interestingly, the inter block repulsion or ab
enhances the solvent quality favoring chain solubility. The second term on the
RHS of Eq. 13 is not sensitive to the polymer/solvent interaction and is
reminiscent of the copolymer architecture. It coincides with the bulk limit by

putting  = 1 or by introducing an effective parameter as ab. If ps increases,

the first term may dominate and eventually diverge at q = 0. The forward

scattering intensity which is proportional to Saa(q = 0 ) increases with  at a

much larger extent for a higher polymer/solvent parameter ps. Its divergence
hints to a macrophase transition as illustrated in Figure 2 where points 1, 2, 3
in part a designate the conditions under which the curves in panel b were
plotted. Curve 3 indicates how the forward scattering signal tends to diverge as
the critical conditions are approached.