Effect of Tapering on Morphology and Interfacial Behavior of Diblock Copolymers from Molecular Dynamics Simulations
Y Seo and JR Brown and LM Hall, MACROMOLECULES, 48, 4974-4982 (2015).
Tapered diblock copolymers are AB diblock copolymers modified by adding a gradient region between the blocks in which composition Varies smoothly from one species to the other. This gives additional control parameters the length:of the taper and its direction, to Control the microphase separation behavior. Using tapers can also increase the accessibility of the bicontinuous gyroid, phase potentially of interest in transport applications. Recently, the phase diagram of theee systems was predicted using self-consistent field theory (SCFT). In this study, we perform coarse-gained molecular dynamics (MD) simulations to investigate both the structural and dynamic properties of tapered diblock copolymers. The MD results are consistent with the SOFT phase diagram, and the density profiles are also similar as a function of taper length and direction. We additionally compute mean squared displacements and end-to-end relaxation times of lamellar systems, and observe individual polymer conformations. Increasing taper length, effectively lowers segregation strength and leads to a smaller domain spacing; the changes in dynamics are also discussed. The short (30%) inverse taper has a significantly shorter domain spacing than the diblock and qualitatively different polymer conformations (chains can fold back and forth across the interface).
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