Nonconventional morphologies in two-length scale block copolymer systems beyond the weak segregation theory

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Soft Matter Physics

Background:

• Linear multiblock copolymers exhibit complex phase transitions, including order-disorder and order-order transitions (ODT and OOT).
• Previous theoretical work predicted a nonconventional sequence of OOTs in specific copolymer architectures under cooling.
• Understanding these transitions is crucial for designing materials with tailored morphologies and properties.

Purpose of the Study:

• To investigate the order-disorder and order-order transitions in linear multiblock copolymers with a two-length scale architecture.
• To compare theoretical predictions from weak segregation theory (WST) with results from self-consistent field theory (SCFT).
• To explore the formation of ordered morphologies and micelle structures in these complex systems.

Main Methods:

• Employed a pseudospectral version of self-consistent field theory (SCFT) for high-precision calculations of block copolymer phase behavior.
• Utilized Ng iterations and predefined symmetries for efficient and accurate convergence of SCFT calculations.
• Analyzed phase diagrams and scattering spectra to identify ordered phases and their temperature dependence.

Main Results:

• The WST-predicted sequence of phase transitions was confirmed for symmetric copolymer tails (mid R:0.5-fmid R:
• A significant region of face-centered cubic phase stability was discovered within the body-centered cubic phase for asymmetric tails (mid R:0.5-fmid R:>0.05).
• Observed the formation of 2D and 3D micellar phases by longer polymer tails, a deviation from conventional diblock copolymers.

Conclusions:

• SCFT calculations provide a more detailed understanding of phase transitions in complex block copolymers compared to WST.
• The architecture of block copolymers significantly influences the formation of ordered phases and micelle structures.
• Non-monotonous temperature dependence of scattering intensities is a common feature in these ordered phases.