Composition fluctuation in weakly heterogeneous dielectric medium containing ions*

Impacts of salt doping on morphological behavior of block polymers, though well-documented, remain poorly understood. Selective ion solvation has been identified as a driving force for ordering, and its effects studied using mean-field models. We present an analysis of the
composition fluctuation that couples, through the heterogeneous dielectric profile, to the ionic solvation in the weakly heterogeneous regime. The free energy is mapped onto the Brazovskii form. The scattering peak is found to depend on salt-doping, as a result of the shift of the
critical point and the pairwise Coulomb interaction. Phase diagrams are presented under different doping conditions, revealing the competition between selective solvation and fluctuation. The need of consistently parameterizing permittivity and dispersion interaction is discussed.