Stretching the limits of high conductivity～High-performing elastic conductor

realized by self-forming Ag nanoparticles～

School of Engineering, The University of TokyoJapan Science and Technology Agency (JST)

RIKENPress releaseMay 11th, 2017

Prof. Takao SomeyaDr. Naoji Matsuhisa

1

Contents

(1) New printable elastic conductors(2) Background, Impact, Future prospect

2

The result will be published in Nature Materialson 15 May 2017 at 16:00 (GMT) / 11:00 (EST), which is when the embargo will be lifted.

Summary

We have developed printable elastic conductors with the world’s highest conductivity (935 S/cm) at a strain of 400% (5 times as long as the original length).

The high performance was obtained by in situ formation of Ag nanoparticles, which resulted by mixing micrometer-sized Ag flakes and a fluorine rubber.

The new material realizes simple integration of stretchable pressure/temperature sensors on textiles, leading to applications in sports wear or robotics. 3

World’s Best Printable Elastic Conductors

4

Formed by a simple printing process.High conductivity (935 S/cm) and stretchability

(400%) are simultaneously obtained.

伸張率

伸張率

World best printable elastic conductors (Movie)

High conductivity is maintained at very large strains, enabling the stable operation of LEDs. 5

Pressuresensor

New printedelastic conductors

Lightemittingdiodes(LEDs)

Stretchable Sensors Fabricated on Textiles

6

The pressure is sensed at the fingertips and the brightness of the LEDs changes with the applied pressure.

Main features

7

Printable (e.g. screen printing, stencil

printing)

Without strain, the materials show a high

conductivity of 4972 S/cm.

With 400％ strain (5 times as long as the

original length), the materials exhibit a world’s

highest conductivity of 935 S/cm.

Fabrication process

8

Organic solvent(Methylisobutylketone)

Ag flakes

Fluorine rubber(DAI-EL, Daikin Industries)

Elastic conductor ink

Fluorine surfactant

Mix

The printed tracesare dried at 80 ℃ for1 h and 120 ℃ for 1 h.

100 nm

Self-formation of Ag nanoparticlesboosts the performance.

(Transmission electron microscope (TEM) image)

Ag flakes

~8-nm Ag nanoparticles are self-formed in high density.

9

The Ag nanoparticles observation was conducted in collaboration with Dr. Daisuke Hashizume, and Mr. Daishi Inoue at RIKEN.

Performance Improvement by Self-Formed Ag Nanoparticles

10

100

101

102

103

104

0 50 100 150 200 250 300

Con

duct

ivity

(S/c

m)

Strain (%)

With self-formed Ag nanoparticles

With dry Agnanoparticlepowder

Self-formation of Ag nanoparticles realizeshigh-performance elastic conductors.

101

102

103

104

0 100 200 300 400 500

Con

duct

ivity

(S/c

m)

Strain (%)

Comparison With Previous Studies[1] T. Sekitani, et al. Nat. Mater.

8, 494–499 (2009).[2] K. Chun, et al. Nat. Nanotechnol.

5, 853–857 (2010).[3] T. Araki, et al. IEEE EDL

32, 1424–1426 (2011).[5] M. Park, et al. Nat. Nanotechnol.

7, 803–809 (2012).[6] Y. Kim, et al. Nature

500, 59–63 (2013).[7] H. Stoyanov, et al. Adv. Mater.

25, 578–83 (2013).[8] R. Ma, et al. ACS nano 9,

10876-10886 (2015).[9] J. Liang et al. Adv. Mater. 28,

5986-5996 (2016).[10] N. Matsuhisa, et al.

Nat. Commun. 6, 7461 (2015).

11

2015

At 400% strain, the world’s highest conductivity(935 S/cm) is achieved. (Without strain, 4972 S/cm)

2017 (This study)New elasticconductor

2009

Installation of stretchable sensors to textiles

2 cm

Large area sensors are easily integrated in textile.

Heat & Press

Fully Printed Stretchable Sensor Sheet (※Temperature sensors can also be fabricated.)

Textilesubstrate Elastic

conductorwiring

12

Pressure Sensors

2 cm

Stretchable pressure sensing textile glove

13

Sensors can be easily installed to the moving parts of robots.

Elastic Conductors Pressure Sensors

2 cm

5 mm

~120% strain

Resist/Polyurethane

Stretch test of stretchable pressure sensors

14

Elastic conductor maintains high conductivity at 250% strain. Stable measurement of pressure.

Pressuresensor

Elastic conductor

2 cm102

103

104

105

106

107

108

0 1 2 3 4 5 6

0%250%

Res

ista

nce

()

Force (N)

Applied strain (%)

250%strain

Mechanism of Ag nanoparticles self-formation

Ag flake

Fluorine rubber+ fluorine surfactant

Ag2O layer

Ag+

Ag+

Ag+

Ag+

Ag+

Ag+

Self-formedAg nanoparticles

Heat

15

Ag flakes are dispersed in the rubber. The surfactant and addition of heat convert the ions to Ag nanoparticles.

Research backgroundImpact

Future prospect

16

Stretchable electronics

17

Stretchable electronic devices（on Textiles, Rubber sheets）Electronics on soft, arbitrary surfaces.

A stretchable wiring with high conductivity and stretchability has been crucial in stretchable devices.

Smart sheet,Smart handle

Automobile

RobotSportTraining,

Injury prevention

MedicalBody

temperature,EMG, ECG

VR・ARHuman computer interfaces

Artificial feeling

Lamination to: Human

Artificial skin/muscle,Soft robots

To: Machine

Development of Elastic Conductors

18

Year 2008 2009 2015 2017(This study)

Conductivity(S/cm) 57 102 182 935

Stretchability(%) 40 118 215 400

Conductive filler(s)

Carbonnanotubes

Carbonnanotubes

Ag flakes

Ag flakes Ag

nanoparticles

PaperT. Sekitani,

T. Someya, et al. Science 321,1468 (2008).

T. Sekitani, T. Someya, et al.

Nature Materials 8,494 (2009).

N. Matsuhisa, T. Someya, et

al. Nature Communicatio

ns 6, 7461 (2015).

N. Matsuhisa, T. Someya, et al. Nature

Materials (2017).

10 years improvement in conductivity (16 times) and stretchability (10 times).

Future prospect

19

Stretchable sensors can be easily attached to soft, arbitrary surfaces.

Various applications include vital information monitoring of the whole body using wearables, and artificial feelings. They will accelerate the fields of sports, healthcare, medical, and robotics.

The self-formation of metal nanoparticles will enhance the performance of various composite materials which include elastic conductors, pressure sensors, and temperature sensors.

Further developments for the practical use

1. Cyclic durability

2. Environmental stabilityeg. Washability, Thermal Stability

3. System level integrationeg. Power Supply, Wireless Communication

20

Publication and press embargoThe result will be published in Nature Materialson 15 May 2017 at 16:00 (GMT) / 11:00 (EST), which is when the embargo will be lifted.

Title“Printable Elastic Conductors by in situ Formation of Silver Nanoparticles from Silver Flakes”

AuthorsNaoji Matsuhisa, Daishi Inoue, Peter Zalar, HanbitJin, Yorishige Matsuba, Akira Itoh, Tomoyuki Yokota, Daisuke Hashizume, and Takao Someyadoi: 10.1038/NMAT4904

21

Funding

This result is an accomplishment of the Exploratory Research for Advanced Technology (ERATO) research funding program.

Project Name:Someya Bio-Harmonized Electronics Project

Project Director:Takao Someya, Professor, School of Engineering, The University of Tokyo

Project Period:August 2011 - March 2017

22

Summary The new printable elastic conductor is 400%

stretchable (5 times as long as the original length), and exhibits the world’s highest conductivity at strains >150%.

The self-formation of Ag nanoparticles boosted the performance of the elastic conductors, which are not originally included in the ink.

Highly stretchable (>250%) pressure/temperature sensors are fully fabricated by printing processes.

The new material will be fully utilized in wearables or artificial skins, with applications in sports, healthcare, medical, and robots. 23

Contact

Professor Takao Someya

Department of Electrical Engineering and Information Systems (EEIS), Graduate School of Engineering, The University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 JAPANSomeya Laboratory, School of Engineering, University of Tokyo

Tel: +81-3-5841-6756Fax: +81-3-5841-6709Email: someya@ee.t.u-tokyo.ac.jp

24