title: Soft Elastomers with Ionic Liquid-Filled Cavities as Strain Isolating Substrates for Wearable Electronics.
abstract: Managing the mechanical mismatch between hard semiconductor components and soft biological tissues represents a key challenge in the development of advanced forms of wearable electronic devices. An ultralow modulus material or a liquid that surrounds the electronics and resides in a thin elastomeric shell provides a strain-isolation effect that enhances not only the wearability but also the range of stretchability in suitably designed devices. The results presented here build on these concepts by (1) replacing traditional liquids explored in the past, which have some nonnegligible vapor pressure and finite permeability through the encapsulating elastomers, with ionic liquids to eliminate any possibility for leakage or evaporation, and (2) positioning the liquid between the electronics and the skin, within an enclosed, elastomeric microfluidic space, but not in direct contact with the active elements of the system, to avoid any negative consequences on electronic performance. Combined experimental and theoretical results establish the strain-isolating effects of this system, and the considerations that dictate mechanical collapse of the fluid-filled cavity. Examples in skin-mounted wearable include wireless sensors for measuring temperature and wired systems for recording mechano-acoustic responses.
authors.affiliation: Department of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA, Department of Engineering Mechanics, Center for Mechanics and Materials, Tsinghua University, Beijing 100084, China.
authors.forename: Yinji
authors.initials: Y
authors.lastname: Ma
authors.affiliation: Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Matt
authors.initials: M
authors.lastname: Pharr
authors.affiliation: Department of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA, Institute of Chemical Machinery and Process Equipment, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Jeonghyun
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Yuhao
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Yeguang
authors.initials: Y
authors.lastname: Xue
authors.affiliation: Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Rui
authors.initials: R
authors.lastname: Ning
authors.affiliation: Department of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA, School of Materials Science and Engineering, Xiangtan University, Hunan, 411105, China.
authors.forename: Xiufeng
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Ha Uk
authors.initials: HU
authors.lastname: Chung
authors.affiliation: Department of Engineering Mechanics, Center for Mechanics and Materials, Tsinghua University, Beijing, 100084, China.
authors.forename: Xue
authors.initials: X
authors.lastname: Feng
authors.affiliation: Department of Materials Science and Engineering, Chemistry, Mechanical Science and Engineering, Electrical and Computer Engineering, Beckman Institute for Advanced Science and Technology, and Frederick Seitz Materials, Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Rogers
authors.affiliation: Department of Civil and Environmental Engineering, Mechanical Engineering, and Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Huang
mesh_terms: D020724:Elastomers / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D000076251:Wearable Electronic Devices; D059015:Wireless Technology
chemical_list: D020724:Elastomers; D052578:Ionic Liquids
keywords: flexible electronics; ionic liquid; stretchable electronics; wearable electronics