Self-assembly of cyclic rod-coil diblock copolymers

Area of Science:

• Polymer Science and Engineering
• Materials Science
• Computational Chemistry

Background:

• Understanding block copolymer phase behavior is crucial for designing advanced materials.
• The effect of chain topology, specifically cyclization, on self-assembly is not fully understood.
• Rod-coil block copolymers present unique challenges and opportunities in self-assembly.

Purpose of the Study:

• To investigate the phase behavior of cyclic rod-coil diblock copolymer melts.
• To compare the self-assembly of cyclic and linear rod-coil systems.
• To elucidate the impact of topological constraints on copolymer phase diagrams and morphologies.

Main Methods:

• Dissipative particle dynamics (DPD) simulations were employed.
• Phase diagrams for both cyclic and linear rod-coil diblock copolymers were calculated.
• Morphologies and molecular arrangements were analyzed at different compositions (frod).

Main Results:

• Cyclic rod-coil diblock copolymers show higher order-disorder transition points (χN)ODT than linear analogs.
• Cyclic systems exhibit more symmetrical phase diagrams due to topological constraints.
• Distinct morphologies were observed: coplanar bilayers in cyclic vs. interdigitated bilayers in linear systems at frod=0.5; hexagonally packed cylinders in cyclic vs. smectic A lamellar phase in linear systems at frod=0.7.
• The domain size ratio of cyclic to linear diblocks in lamellar phases ranges from 0.63 to 0.70.
• Cyclic architecture restricts coil chain expansion and increases inter-block contacts.

Conclusions:

• Cyclization significantly alters the phase behavior and self-assembly of rod-coil block copolymers.
• The topological constraint of cyclization leads to unique morphologies and properties.
• These findings offer pathways to diversify physical properties and applications of block copolymers.