Reentrant phase behavior and coexistence in asymmetric block copolymer electrolytes

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Addition of salts to symmetric block copolymers typically stabilizes ordered phases.
• This stabilization is attributed to an increased effective Flory-Huggins interaction parameter (χ).
• The behavior of asymmetric block copolymers in response to salt addition is less understood.

Purpose of the Study:

• To investigate the effect of salt concentration on the self-assembly of disordered asymmetric block copolymers.
• To elucidate the complex phase transitions induced by salt addition.
• To compare the behavior of different asymmetric block copolymers and assess theoretical models.

Main Methods:

• Systematic variation of salt concentration in asymmetric block copolymers.
• Characterization of resulting phases using techniques like electron tomography.
• Analysis of domain spacing and phase behavior as a function of salt concentration.

Main Results:

• Disordered asymmetric block copolymers exhibit reentrant phase behavior upon salt addition.
• Formation of coexisting body-centered cubic (BCC) phases with different domain spacings at intermediate salt concentrations.
• A disorder-to-order transition to hexagonally packed cylinders at high salt concentrations.
• Non-monotonic domain spacing dependence on salt concentration, indicating potential reentrant transitions.

Conclusions:

• Salt addition to asymmetric block copolymers leads to complex, non-monotonic phase behavior, including reentrant disordered phases.
• Observed phenomena, such as coexisting BCC phases and hexagonal cylinders, challenge traditional theories based on effective Flory-Huggins parameter (χ).
• Non-monotonic domain spacing dependence serves as an indicator for reentrant phase transitions in block copolymer electrolytes.