Relaxation processes in a lower disorder order transition diblock copolymer

Area of Science:

• Polymer Science
• Materials Science
• Soft Matter Physics

Background:

• Diblock copolymers exhibit complex phase behavior, transitioning between disordered and ordered states.
• Understanding the dynamics during phase separation is crucial for controlling material properties.
• Lower disorder-order transitions (LDOT) present unique dynamic behaviors distinct from upper transitions.

Purpose of the Study:

• To characterize the dynamic modes of diblock copolymers undergoing phase separation at lower disorder-order transitions (LDOT).
• To compare the observed dynamics with theoretical predictions for upper disorder-order transitions.
• To investigate the universality of dynamic modes in compressible versus incompressible block copolymer systems.

Main Methods:

• X-ray photon correlation spectroscopy (XPCS) was employed to probe dynamics.
• Experiments were conducted across various temperatures relative to the disorder-to-order transition.
• Analysis focused on identifying diffusive and non-diffusive dynamic modes.

Main Results:

• A non-diffusive mode, attributed to compositional fluctuations, was observed below the disorder-to-order transition, slowing with increased interaction.
• Above the transition, a diffusive mode, linked to chain segment diffusion across interfaces, dominated.
• Both modes, previously predicted for upper transitions, were found in compressible LDOT systems, suggesting broader applicability.
• In the ordered state, only the diffusive mode persisted, related to interphase segment transport.

Conclusions:

• The study demonstrates the presence of two distinct dynamic modes (non-diffusive and diffusive) in compressible LDOT diblock copolymers.
• These findings suggest a universality in block copolymer dynamics beyond theoretical predictions for upper transitions.
• The experimental results provide valuable data for developing theories on dynamics in LDOT systems.