Highly stretchable and transparent ionogels as nonvolatile conductors for dielectric elastomer transducers.

Large deformation of soft materials is harnessed to provide functions in the nascent field of soft machines. This paper describes a new class of systems enabled by highly stretchable, transparent, stable ionogels. We synthesize an ionogel by polymerizing acrylic acid in ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([C2mim][EtSO4]). The ionogel exhibits desired attributes of adequate conductivity (0.22 S m(-1)), low elastic modulus (∼3 kPa), large rupturing stretch (∼4.6), and negligible hysteresis and degradation after cyclic stretches of large amplitude. Using the ionogel and a dielectric elastomer, we fabricate electromechanical transducers that achieve a voltage-induced areal strain of 140%. The ionogel is somewhat hygroscopic, but the transducers remain stable after a million cycles of excitation in a dry oven and in air. The transparency of the ionogels enable the transducers with conductors placed in the path of light, and the nonvolatility of the ionogels enable the transducers to be used in open air.

[1]  Philip G. Whitten,et al.  High strain stretchable solid electrolytes , 2013 .

[2]  Lydie Viau,et al.  Ionogels, ionic liquid based hybrid materials. , 2011, Chemical Society reviews.

[3]  D. De Rossi,et al.  Bioinspired Tunable Lens with Muscle‐Like Electroactive Elastomers , 2011 .

[4]  Ugo Bardi,et al.  Ionic liquids for hybrid supercapacitors , 2004 .

[5]  Takayuki Kitamura,et al.  Quasi-solid-state dye-sensitized solar cells using room temperature molten salts and a low molecular weight gelator. , 2002, Chemical communications.

[6]  Yong-Lae Park,et al.  A Soft Strain Sensor Based on Ionic and Metal Liquids , 2013, IEEE Sensors Journal.

[7]  Benjamin C. K. Tee,et al.  25th Anniversary Article: The Evolution of Electronic Skin (E‐Skin): A Brief History, Design Considerations, and Recent Progress , 2013, Advanced materials.

[8]  Todd A. Gisby,et al.  Multi-functional dielectric elastomer artificial muscles for soft and smart machines , 2012 .

[9]  Zhigang Suo,et al.  Dielectric elastomer actuators with elastomeric electrodes , 2012 .

[10]  T. Lodge,et al.  High‐Capacitance Ion Gel Gate Dielectrics with Faster Polarization Response Times for Organic Thin Film Transistors , 2008 .

[11]  Z. Suo.  Mechanics of stretchable electronics and soft machines , 2012 .

[12]  Stephen A. Morin,et al.  Camouflage and Display for Soft Machines , 2012, Science.

[13]  P. Soudan,et al.  Solid‐State Electrode Materials with Ionic‐Liquid Properties for Energy Storage: the Lithium Solid‐State Ionic‐Liquid Concept. , 2011 .

[14]  Sigurd Wagner,et al.  Characterization of an Elastically Stretchable Microelectrode Array and Its Application to Neural Field Potential Recordings , 2009 .

[15]  M. Kaltenbrunner,et al.  An ultra-lightweight design for imperceptible plastic electronics , 2013, Nature.

[16]  Jong‐Min Lee,et al.  Applications of ionic liquids. , 2012, Chemical record.

[17]  Peter Sommer-Larsen,et al.  Mechanical properties of dielectric elastomer actuators with smart metallic compliant electrodes , 2002, SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring.

[18]  Jonathan N. Coleman,et al.  Very thin transparent, conductive carbon nanotube films on flexible substrates , 2010 .

[19]  K. Bertoldi,et al.  A Bioinspired Soft Actuated Material , 2014, Advanced materials.

[20]  Q. Pei,et al.  High-speed electrically actuated elastomers with strain greater than 100% , 2000, Science.

[21]  George M. Whitesides,et al.  Camouflage and Display for Soft Machines , 2012, Science.

[22]  P. Calvert.  Hydrogels for Soft Machines , 2009 .

[23]  H. Shea,et al.  Flexible and stretchable electrodes for dielectric elastomer actuators , 2012, Applied Physics A.

[24]  Ron Pelrine,et al.  Dielectric elastomers: Stretching the capabilities of energy harvesting , 2012 .

[25]  Zhibin Yu,et al.  Bistable Large‐Strain Actuation of Interpenetrating Polymer Networks , 2012, Advanced materials.

[26]  Qibing Pei,et al.  Highly stretchable, conductive, and transparent nanotube thin films , 2009 .

[27]  Nicola Pugno,et al.  Multifunctionality and Control of the Crumpling and Unfolding of Large-Area Graphene , 2012, Nature materials.

[28]  D. Clarke,et al.  Tunable lenses using transparent dielectric elastomer actuators. , 2013, Optics express.

[29]  Choon Chiang Foo,et al.  Stretchable, Transparent, Ionic Conductors , 2013, Science.

[30]  Rajesh Rajamani,et al.  Carbon nanotube-based transparent thin film acoustic actuators and sensors , 2006 .

[31]  Raeed H. Chowdhury,et al.  Epidermal Electronics , 2011, Science.

[32]  John R. Buck,et al.  An elastomeric ionic hydrogel sensor for large strains , 2012, 2011 IEEE 37th Annual Northeast Bioengineering Conference (NEBEC).

[33]  Choon Chiang Foo,et al.  Cyclic performance of viscoelastic dielectric elastomers with solid hydrogel electrodes , 2014 .

[34]  P. Wasserscheid,et al.  Ionic liquids in chemical engineering. , 2010, Annual review of chemical and biomolecular engineering.