Nano Focus: Electrostatic control achieved in block copolymers through morphology
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he development of energy conversion and storage devices is at the forefront of research geared toward a sustainable future. However, materials limitations serve as bottlenecks in this progress. Typical liquid electrolytes used for the transport of ions between an anode and cathode are highly flammable and pose a safety hazard. Research efforts have focused on exploring solid electrolytes that do not have these limitations. Block copolymers are an alternative as solid electrolytes because they can self-assemble into nanostructures, which enables ion transport and maintains structural integrity. Furthermore, the ion conductivity can be controlled according to the nanostructure geometry. Researchers Charles E. Sing, Jos W. Zwanikken, and Monica Olivera de la Cruz from Northwestern University have used a theoretical model to demonstrate that the distribution of charge on the blocks comprising block copolymer systems can be used to manipulate the copolymer through inducement of an array of nanostructures. As reported in the July issue of Nature Materials (DOI: 10.1038/NMAT4001; p. 694), the
t Mechanical metamaterials produce ultralight, ultrastiff lattices
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he word “metamaterial” conjures up visions of matter interacting with electromagnetic waves to bend the waves around objects, producing a “cloaking device” that hides the object from detection. But the “mechanical metamaterials” that Chris Spadaccini’s group at Lawrence Livermore National Laboratory and Nicholas Fang’s team at the Massachusetts Institute of Technology (MIT) are working on aim to avoid bending as much as possible—mechanical bending, that is. Instead, by causing forces to distribute only in stretching or compression modes
researchers varied the charge density along the block copolymer backbone through straightforward design of parameters. Charges along one of the blocks as well as the corresponding counterions dictate the equilibrium properties of the block copolymers through a combination of entropy, ion solubility, and Increase Coulombic electrostatic cohesion, which Interaction taken together drastically manipulate the phase behavior. The accompanying figure depicts the effect of charge cohesion on nanostructure phase behavior, demonstrating that highly asymmetric charge cohesion effects can induce the formation of nanostructures that are inaccessible to conventional uncharged block copolymers, Effect of charge cohesion on nanostructure phase behavior showing electrostatic cohesion between the charged including percolated phases A-blocks and the counterions. When the interactions are desired for ion transport. strong, the components are electrostatically correlated in a liquid-like ordered structure, which has a significant This work presents an oreffect on the phase diagram. Reproduced with permisthogonal route toward tuning sion from Nat. Mater. 13 (2014), DOI: 10.1038/nmat4001. nanostructures that will have © 2014 Macmillan Publishers Ltd. a significant impact on the design of block copolymer mafiltration membranes, and materials with ter
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