Phase behavior of AB/CD diblock copolymer blends via coarse-grained simulation

• Published in: Soft matter 2020-03, Vol.16 (12), p.3069-3081
• Main Authors: Ahmadian, Iman, Peters, Andrew J
• Format: Article
• Language: English
• Subjects: Block copolymers; Concentric spheres; Cylinders; Domains; Eigenvalues; Lamellae; Lamellar structure; Mixtures; Morphology; Phase diagrams; Separation; Simulation; Tensors
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/d0sm00096e

The phase diagram of equimolar blends of AB and CD diblock copolymers has been studied using dissipative particle dynamics. All unlike blocks interacted with the same χ, except for the B-C interaction, for which χ < 0 in order to prevent macrophase separation. The BC interaction was able to prevent macrophase separation except for low volume fractions of B and C (φ ⪅ 0.1) and relatively equal fractions of A and D. For high φ (φ ⪆ 0.92), a disordered state was obtained. For all microphase separated states the shapes/morphologies were described by the ratios of the eigenvalues of the radius of gyration tensor and their sphericity. These were used to classify the domains as forming sphere, cylinders, lamellae, or branched/gyroidal structures. For φ < 0.5 the BC domains acted as an interfacial region which compatibilized the A and D domains, while for φ > 0.5 the BC domain filled in the space between A and D domains. Several interesting structures were formed including a novel connected/branched spheres morphology, hierarchical lamellae, concentric spheres/cylinders, and a combination of cylinders/lamellae. Comparisons are made with the linear diblock and linear triblock phase diagrams.