442767 Using Fluids Density-Functional Theory to Investigate the Structure of Linearly-Tapered Diblock Copolymers

Monday, November 9, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Tiara Ann D. Maula1, Lisa M. Hall2 and Jonathan R. Brown2, (1)William G. Lowrie Department of Chemical Engineering, Ohio State University, Columbus, OH, (2)The Ohio State University, Columbus, OH

An increasing number of applications require the use of materials with a very precise structure, sometimes down to the nanometer scale. The physical limitations of directly fabricating such materials are obvious; however, self-assembling materials provide a means to fabricate nanostructured materials with the potential for mass production. Diblock copolymers, composed of blocks of two chemically different monomers A and B bonded together in the same chain, are well known to self-assemble into various microscopically ordered structures. In this research, classical fluids density functional theory (fDFT) was used to study the morphology of 50% linearly-tapered diblock copolymers (containing a linear gradient in composition from A to B between the pure A and B blocks). In the applications of interest such as robust and nonflammable battery electrolytes, A would allow for ion diffusion and B would provide mechanical strength. Specifically, we investigated the effect of chain length N and unfavorable A-B interaction strength (quantified by the Flory parameter χ) on the equilibrium density profiles of lamellar (layered) systems, with a special focus on the lamellar spacing, Lz. The polymers studied had chain lengths from N = 24 to 120 beads and A-B repulsive strengths that map to χ = 0.25 to 1.5. We find that when the lamellar spacing is normalized by √N and plotted against the segregation strength χN, the results for all systems collapse onto a single curve. Besides enhancing present knowledge relevant to the design of novel materials, the fDFT results can be used to initialize more detailed and computationally intensive molecular dynamics simulations.

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