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Structure and Thermodynamics of Hybrid Organic-Inorganic Diblock Copolymers with Salt
Sethi, Gurmukh K.,Jung, Ha Young,Loo, Whitney S.,Sawhney, Simar,Park, Moon Jeong,Balsara, Nitash P.,Villaluenga, Irune American Chemical Society 2019 Macromolecules Vol.52 No.9
<P>We examine the phase behavior of a hybrid organic-inorganic diblock copolymer/salt mixtures. The experimental system comprises poly(ethylene oxide)-<I>block</I>-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<SUB>eff</SUB>, for the electrolytes. Unlike conventional systems, χ<SUB>eff</SUB> increases with increasing temperature. A simple expression is proposed to describe the dependence of χ<SUB>eff</SUB> on temperature and salt concentration. This enables the calculation of the segregation strength, χ<SUB>eff</SUB><I>N</I>, for both ordered and disordered electrolytes. The composition of the electrolytes is quantified by <I>f</I><SUB>EO/LiTFSI</SUB>, the volume fraction of the salt-containing poly(ethylene oxide)-rich phase. The morphology of electrolytes is presented on a χ<SUB>eff</SUB><I>N</I> versus <I>f</I><SUB>EO/LiTFSI</SUB> phase diagram. Over the values of <I>f</I><SUB>EO/LiTFSI</SUB> studied (0.61-0.91), only two ordered phases were found: lamellae and co-existing lamellae/hexagonally packed cylinders.</P> [FIG OMISSION]</BR>