(121c) Electrostatic Screening Effects in a Salt-Doped Polarizable Diblock Copolymer

We study a salt-doped polarizable symmetric diblock copolymer using a recently-developed polarizable field theory that self-consistently embeds dielectric response, ion solvation energies and van der Waals (vdW) attractions via the attachment of classical Drude oscillators to the constituent fluid elements. This field theory is amenable to direct simulation via the complex Langevin sampling technique, which requires no approximations beyond the phenomenology of the underlying coarse-grained model. We measure the shift in the order-disorder transition (ODT) with salt-loading in field-theoretic simulations and observe rich behavior in which solvation, dilution and charge screening effects compete to determine whether the ordered or disordered phase is stabilized. At low salt concentrations, the salt behaves as a selective solvent, localizing into the high-polarizability domains as expected. At high salt concentrations, however, the salt localization vanishes due to charge screening effects and the salt behaves as a non-selective solvent that screens vdW attractions and stabilizes the disordered phase. This is the first simulation-based investigation into the phase behavior of salt-doped polymers in which the solvation physics emerges self-consistently from explicit ion-dipole interactions. Our results raise questions regarding the conditions under which it is appropriate to ignore the screening effect of the ion cloud in theories of salt-doped polymers.