Sliding chains keep particles together

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Science  21 Jul 2017:
Vol. 357, Issue 6348, pp. 250-251
DOI: 10.1126/science.aan6685

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Pulleys, first devised in the 3rd century BCE, make it easy to reverse the direction of a lifting force in a fixed axle or to mitigate the work required to lift an object with multiple wheels in a movable state. Pulleys distribute localized force to parallel chains, which greatly reduces the stress on any single strand. Constructing pulleys at the molecular level with small functional materials, especially polymers, is still challenging (1, 2). On page 279 of this issue, Choi et al. (3) describe a class of polymer that imitates the basic principle of a pulley's operation. The primary chain is chemically bonded to a polymer ring threaded by a secondary chain. This material shows promise as a chemical glue—the so-called binder—in batteries that accommodates the volume changes of electrode particles during charging and discharging.