Effects of lithium salts on the lamellar phase of diblock copolymers

We study the effects of lithium salts on the lamellar phase of AB diblock copolymers by means of the self-consistent field theory. We consider a model in which the A and B blocks have different dielectric constants and account for the tight binding of Li$^+$ to one of the blocks, the preferential solvation energy of anions in the higher-dielectric polymer domain, the translational entropy of anions, and change in the $\chi$ parameter due to the binding of Li$^+$. We study the effect of the strong polymer-Li$^+$ binding on the distribution of the salt ions. In particular, we show that local charge separation near the interface of the higher- and lower- dielectric polymers largely arises from the effect of the Born energy. We also examine the relationship between two definitions of the effective $\chi$ parameter, one based on the lamellar spacing and one based on the structure factor in the disordered phase, and show that these two definitions generally do not coincide.