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Published August 26, 2014 | public
Journal Article

Evolution of Grain Structure during Disorder-to-Order Transitions in a Block Copolymer/Salt Mixture Studied by Depolarized Light Scattering


Block copolymer/lithium salt mixtures are promising materials for lithium battery electrolytes. The growth of ordered lamellar grains after a block copolymer electrolyte was quenched from the disordered state to the ordered state was studied by depolarized light scattering. Three quench depths below the order-to-disorder transition temperature were studied: 6, 12, and 24 °C. Regardless of quench depth, elongated ellipsoidal grains with aspect ratios between six and eight were formed during the initial stage of order formation. This was followed by a rapid reduction in aspect ratio; at long times, isotropic grains with aspect ratios in the vicinity of unity were obtained. Unusual grain growth kinetics were observed at all quench depths: (1) The average grain volume decreased with time after the early stage of grain growth. To our knowledge, a decrease in grain size has never been observed before in any quenched block copolymer system. (2) The volume fraction occupied by ordered grains of the shallowest quenched sample (quench depth of 6 °C) was significantly less than unity even after waiting times approaching 400 min. This is consistent with recent theoretical and experimental work indicating the presence of a coexistence window between ordered and disordered phases due to the partitioning of the salt into the ordered domains. At quench depths of 12 and 24 °C, which are outside the coexistence window, the grain volume fraction increases monotonically with time, and ordered grains occupy the entire sample at long times.

Additional Information

© 2014 American Chemical Society. The authors acknowledge the generous support of the National Science Foundation through Award Numbers DMR-0966626, DMR-0966765, and CBET-0965812. Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the National Science Foundation. The assistance of Mr. Hao-Chun Chiang in solving some programming problems is also appreciated. The authors declare no competing financial interest.

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