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Block copolymer/lithium salt mixtures are an emerging class of lithium battery electrolytes. Previous studies have shown that the ionic conductivity of these materials is a sensitive function of grain size. Both depolarized light scattering (DPLS) and small-angle X-ray scattering (SAXS) have proven to be effective techniques for elucidating the grain structure of block copolymer (BCP) materials. DPLS is particularly useful for the characterization of samples with grain sizes larger than 1 μm, whereas SAXS is particularly well suited for samples with grain sizes smaller than 0.1 μm. We present the results of both DPLS and SAXS measurements of grain structure in a BCP/lithium salt mixture that was annealed after being initially prepared by freeze-drying from solution. The combination of the two techniques demonstrates that our sample is characterized by an extremely wide distribution of grain sizes. In particular, the sample has a large population of small sub-micrometer-sized grains that cannot be detected optically. A bimodal grain distribution model is presented to support this interpretation of the experimental data. The presence of both large grains and regions of undetectable small grains was confirmed by polarized optical microscopy (POM). Two-wavelength DPLS measurements provide an additional approach for characterizing block copolymer samples with a broad distribution of grain sizes. [ABSTRACT FROM AUTHOR]

The grain structure of ordered block copolymer materials affects their viscoelastic, adhesive, optical, and electrical properties. Depolarized light scattering has proven to be an important method for characterizing this grain structure. In this paper, we use both theory and experiments to demonstrate the relationship between grain structure and depolarized light scattering from ordered block copolymer samples performed with crossed circular polarizers. We model the sample assuming it comprises randomly oriented ellipsoidal grains with optic axes coincident with the ellipsoid axes. We show that the scattering pattern obtained using circularly polarized (CP) light is azimuthally symmetric, in contrast to that obtained using linearly polarized (LP) light which exhibits 4-fold angular modulation. The integrated scattered power in the CP case is twice as large as that in the LP case. By simultaneously fitting CP and LP light scattering data, we obtain robust measures of parameters that characterize grain structures. In addition, CP light scattering can, in principle, be used to characterize nonrandom grain orientation distributions. [ABSTRACT FROM AUTHOR]

Block copolymer/lithium salt mixturesare promising materials forlithium battery electrolytes. The growth of ordered lamellar grainsafter a block copolymer electrolyte was quenched from the disorderedstate to the ordered state was studied by depolarized light scattering.Three quench depths below the order-to-disorder transition temperaturewere studied: 6, 12, and 24 °C. Regardless of quench depth, elongatedellipsoidal grains with aspect ratios between six and eight were formedduring the initial stage of order formation. This was followed bya rapid reduction in aspect ratio; at long times, isotropic grainswith aspect ratios in the vicinity of unity were obtained. Unusualgrain growth kinetics were observed at all quench depths: (1) Theaverage grain volume decreased with time after the early stage ofgrain growth. To our knowledge, a decrease in grain size has neverbeen observed before in any quenched block copolymer system. (2) Thevolume fraction occupied by ordered grains of the shallowest quenchedsample (quench depth of 6 °C) was significantly less than unityeven after waiting times approaching 400 min. This is consistent withrecent theoretical and experimental work indicating the presence ofa coexistence window between ordered and disordered phases due tothe partitioning of the salt into the ordered domains. At quench depthsof 12 and 24 °C, which are outside the coexistence window, thegrain volume fraction increases monotonically with time, and orderedgrains occupy the entire sample at long times. [ABSTRACT FROM AUTHOR]