(551b) Composition Fluctuation in Weakly Heterogeneous Salt-Doped Diblock Copolymer

Salt-doped block copolymer is an important candidate for solid electrolytes. Though the effects of salt-doping on the morphological behavior of block copolymer is well documented, the underlying physics remains poorly understood. Selective ion solvation has been identified to promote ordering, and has been treated at the mean-field level. We examine the composition fluctuation by developing a weak segregation theory, in which the composition of polymeric species is coupled to the solvation free energy of ions through the heterogeneous dielectric profile. The variation of characteristic scattering peak with degree of salt-doping is presented, and rationalized by balancing various free energy contributions. The fluctuation effects on ordering is treated within the BrazovskiÄ­ framework. Both mean-field and corrected phase diagrams are presented, revealing the non-trivial competition between selective solvation and composition fluctuations.