Structure and Thermodynamics of Hybrid Organic–Inorganic Diblock Copolymers with Salt
Published Web Locationhttps://doi.org/10.1021/acs.macromol.9b00042
We examine the phase behavior of a hybrid organic-inorganic diblock copolymer/salt mixtures. The experimental system comprises poly(ethylene oxide)-block-polyhedral oligomeric silsesquioxane (PEO-POSS) mixed with a lithium bis(trifluoromethane sulfonyl) imide (LiTFSI) salt. Although the diblock copolymers without salt exhibit a classical order-to-disorder transition behavior with increasing temperature, the PEO-POSS/salt mixtures exhibit disorder-to-order transitions with increasing temperature. The analysis of a small-angle X-ray scattering data from the disordered state using Leibler's random phase approximation enables the determination of an effective Flory-Huggins interaction parameter, χ eff , for the electrolytes. Unlike conventional systems, χ eff increases with increasing temperature. A simple expression is proposed to describe the dependence of χ eff on temperature and salt concentration. This enables the calculation of the segregation strength, χ eff N, for both ordered and disordered electrolytes. The composition of the electrolytes is quantified by f EO/LiTFSI , the volume fraction of the salt-containing poly(ethylene oxide)-rich phase. The morphology of electrolytes is presented on a χ eff N versus f EO/LiTFSI phase diagram. Over the values of f EO/LiTFSI studied (0.61-0.91), only two ordered phases were found: lamellae and co-existing lamellae/hexagonally packed cylinders.