Ordered phases of diblock copolymers in selective solvent.

Area of Science:

• Physical Chemistry
• Materials Science
• Soft Matter Physics

Background:

• Copolymer-solvent mixtures exhibit complex phase behavior.
• Micelle formation and ordering are critical in solution properties.
• Understanding lattice transitions is key to controlling material properties.

Purpose of the Study:

• To develop a mean-field model for micelle aggregation and lattice selection.
• To investigate equilibrium coupling between micelle structure and phase behavior.
• To elucidate the mechanisms driving transitions between ordered micellar phases.

Main Methods:

• Development of a mean-field theoretical model.
• Analysis of thermotropic and lyotropic phase transitions.
• Investigation of lattice phonon entropy and intermicelle repulsions.

Main Results:

• The model predicts transitions from face-centered cubic to body-centered cubic phases for spherical micelles.
• These transitions align with experimental observations across various conditions.
• Two mechanisms explain the stability of the non-close-packed phase: phonon entropy and repulsion preferences.

Conclusions:

• The study provides insights into the relationship between micelle structure ('crewcut' vs. 'hairy') and long-range order.
• Reduced solvent selectivity drives micelle aggregation decrease and lattice density increase.
• The findings enhance understanding of phase transitions in ordered micellar solutions.