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Structure–property–process relationships are a controlling factor in the performance of materials. This offers opportunities in emerging areas, such as stretchable conductors, to control process conditions during printing to enhance performance. Herein, by systematically tuning direct ink write (DIW) process parameters, the electrical conductivity of multiphase liquid metal (LM)-silver stretchable conductors is increased by a maximum of 400% to over 1.06 × 106 S·m–1. This is achieved by modulating the DIW print velocity, which enables the in situ elongation, coalescence, and percolation of these multiphase inclusions during printing. These DIW printed filaments are conductive as fabricated and are soft (modulus as low as 1.1 MPa), stretchable (strain limit >800%), and show strain invariant conductivity up to 80% strain. These capabilities are demonstrated through a set of electromagnetic induction coils that can transfer power wirelessly through air and water, even under deformation. This work provides a methodology to program properties in stretchable conductors, where the combination of material composition and process parameters leads to greatly enhanced performance. This approach can find use in applications such as soft robots, soft electronics, and printed materials for deformable, yet highly functional devices.
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A printed highly stretchable supercapacitor by a combination of carbon ink and polymer network
A supercapacitor requires two electronic conductors with large surface areas, separated by an ionic conductor. Here we demonstrate a method to print a highly stretchable supercapacitor. We formulate an ink by mixing graphene flakes and carbon nanotubes with an organic solvent, and use the ink to print two interdigitated electronic conductors on the surface of a dielectric elastomer. We then submerge the printed electronic conductors in an aqueous solution of monomer, photoinitiator, crosslinker, and salt. The organic solvent and water form a binary solvent in which the ions are mobile. Upon UV irradiation, a polymer network forms. In each printed electrode, the graphene flakes and carbon nanotubes form a percolating network, which interpenetrates the polymer network. The electronic and ionic conductors form large interfacial areas. When the supercapacitor is stretched, the graphene flakes and carbon nanotubes slide relative to one another, and the polymer network deforms by entropic elasticity. The polymer network traps individual graphene flakes and carbon nanotubes, so that repeated stretch neither breaks the percolating network nor shorts the two electrodes. The supercapacitor maintains 88% the initial capacitance after 1600 cycles of stretch to five times its initial dimension. The interpenetration of a covalent network of elastic polymer chains and a percolating network of conductive particles is generally applicable for making stretchable ionotronic devices.
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- Award ID(s):
- 2011754
- PAR ID:
- 10499968
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Extreme Mechanics Letters
- Volume:
- 49
- Issue:
- C
- ISSN:
- 2352-4316
- Page Range / eLocation ID:
- 101459
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1016/j.eml.2021.101459
