Field-Theoretic Study of Salt-Induced Order and Disorder in a Polarizable Diblock Copolymer

Area of Science:

• Polymer physics
• Soft matter physics
• Computational chemistry

Background:

• Diblock copolymers exhibit order-disorder transitions (ODT) influenced by various factors.
• Understanding salt's effect on these transitions is crucial for material design.
• Previous models often simplified the complex interplay of dielectric, solvation, and van der Waals forces.

Purpose of the Study:

• To investigate the impact of salt doping on the ODT of polarizable symmetric diblock copolymers.
• To develop and utilize a field theory that self-consistently includes dielectric response, ion solvation, and van der Waals attractions.
• To explore the competing effects of solvation, dilution, and charge screening on phase stability.

Main Methods:

• Utilized a recently developed field theory incorporating segment polarizabilities and fixed dipoles.
• Employed complex Langevin sampling for direct simulation without phenomenological approximations.
• Performed field-theoretic simulations to measure the shift in ODT with varying salt concentrations.

Main Results:

• Observed rich phase behavior dependent on salt concentration.
• At low salt concentrations, salt localized in high-dielectric domains, stabilizing the ordered phase (selective solvent effect).
• At high salt concentrations, charge screening diminished salt localization, leading to a nonselective solvent behavior that stabilized the disordered phase by screening van der Waals attractions.

Conclusions:

• Salt doping significantly alters diblock copolymer phase behavior through competing mechanisms.
• The transition from selective to nonselective solvent behavior is driven by salt concentration and charge screening.
• The developed field theory provides a robust framework for simulating complex polymer systems with electrostatic and vdW interactions.