Confined versus Unconfined Crystallization in Block Copolymer/Salt Mixtures Studied by Depolarized Light Scattering

Crystallization in an ordered lamellar diblock copolymer/salt mixture, polystyrene-block-poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (SEO/LiTFSI), has been studied using a combination of small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and depolarized light scattering (DPLS). Such materials have applications as electrolyte membranes in solid-state lithium batteries. The grain structure of the electrolyte was controlled by manipulating thermal history. Poly(ethylene oxide) (PEO) crystallization was confined within the microphase-separated morphology and did not affect the grain structure in the case of shallow quenches. Deep quenches resulted in unconfined crystallization, where crystal formation does not affect the microphase-separated morphology but does alter the grain structure. The difference between the two modes of crystallization can only be detected by DPLS. This knowledge is particularly relevant for nanostructured electrolytes where...