A detailed understanding of the phase behavior of block copolymer/ionic liquid mixtures is an important step towards the eventual implementation of these materials into commercial devices.1, 2 To this end, the lyotropic phase behavior of five low molecular weight polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymers has been studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (EMIM Tf2N) across an extensive concentration range. The ordered microstructures formed by the mixtures were characterized with small-angle X-ray scattering at 25 °C. As the concentration of EMIM Tf2N was increased, each of the block copolymers, which were disordered (D) when neat, transitioned through a number of well-defined classical block copolymer morphologies, including: lamellar (L), gyroid (G), hexagonally packed cylinders (H) and spheres packed onto a body-centered-cubic lattice (SBCC). The solutions also exhibited several regions of coexisting microstructures, in addition to a wide region which appears to correspond to a disordered network morphology (N). EMIM Tf2N was found to be strongly selective for PMMA, and thus resides almost exclusively in the PMMA domains of the phase separated microstructures. From this data an effective interaction parameter (χeff) was calculated between the PS and EMIM Tf2N solvated PMMA domains, which we used to generate an experimental phase diagram for PS-b-PMMA in EMIM Tf2N over the weak/intermediate segregation regime (Figure 1). We believe this will prove to be an important tool in future studies of these materials which intend to achieve a particular self-assembled morphology for a specific application. (1) Ye, Y.-S.; Rick, J.; Hwang, B.-J. J. Mater. Chem. A 2013, 1, (8), 2719-2743. (2) Hallinan, D. T.; Balsara, N. P. Annu. Rev. Mater. Res. 2013, 43, (1), 503-525.

Mapping the lyotropic phase behavior of diblock copolymer iongels

249th National Meeting (2015)

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