Weakening of solvation-induced ordering by composition fluctuation*

Selective ion solvation has been identified as a driving force for enhanced ordering in salt-doped block polymers. Recent comparison between mean-field theory and experimental results suggests that the degree of enhancement is limited, necessitating the use of a solvation radius that is larger than physical ion size. Following the standard Brazovskii treatment, we show that this weakened solvation may be partially caused by the composition fluctuation near the ordering transition. The competition between solvation-induced ordering and destabilizing fluctuation effects is revealed by phase diagrams generated at different salt doping conditions. Further, the salt-doping is found to affect the location of the scattering peak non-monotonically, also due to the competition between solvation and fluctuation.