Conference Programme

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R-04: Stretchable Electrodes
Tuesday, 20/Jun/2017:
1:30pm - 3:30pm

Session Chair: Chengkuo Lee, National University of Singapore
Session Chair: Unyong Jeong, Pohang University of Science and Technology
Location: Rm 303

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1:30pm - 2:00pm

Stretchable Conducting Polymer Composites for Wearable Sensor Platforms

Unyong JEONG, Insang YU, Sangbaie SHIN

Pohang University of Science and Technology, South Korea

The Folding and stretching will be the key characteristics in the next-generation electronic devices. The stretchable electronics have motivated scientists to develop deformable materials for use in electrodes, semiconductors, bio-interfaces, and sensors. To realize fully stretchable electronic devices, each component of the device must maintain its performance up to a critical strain. This talk will present recent developments of stretchable conductors and devices which are based on deformable polymer-metal composite materials, deformable conducting polymers, and stretchable polymer semiconductors. This talk will introduce several strategies to generate the patterned composites for highly stretchable electronics. Special focuses will be put on the thermoplastic block copolymer composites.

The strethcable conductors will be used as a circuits and electrodes for s sensor platform. This study presensts several uses of the conductive composites, including a stretchable film-type battery and triboelectric energy harvesting as the power source for wearable sensors, stretchable electrochemical color display, and a real-time apex cardiogram sensor for wearavle healthcare monitoring.

2:00pm - 2:15pm

Stretchable Conductive Composites Based on Intrinsically Conductive Polymer

Pengcheng LI, Rui ZHOU, Donghe DU, Zeng FAN, Jianyong OUYANG

Department of Materials Science and Engineering, National University of Singapore, Singapore

Stretchable and conductive materials can have important application in many areas, such as soft robots, wearable electronics and healthcare devices. However, traditional conductors like metals are not stretchable, while traditional elastomers like polyurethane (PU) and poly(dimethylsiloxane) (PDMS) are not conductive. Therefore, it is significant to develop new materials with both high stretchability and high conductivity. Conductive polymers such as poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) can be good candidates for stretchable electrodes as for their high conductivity and easy solution processability. However due to their rigid conjugated backbone, conductive polymers have high mechanical flexibility but limited elasticity which limited its application as stretchable conductive materials. Here, highly conductive and stretchable polymer films were developed by blending a conductive polymer PEDOT:PSS, with highly stretchable waterborne polyurethane (WPU). These two polymers have good miscibility at a wide range of blending ratios. The conductivity of the composite films increases while the stretchability decreases with the increase of PEDOT:PSS loading. This kind of stretchable conductive composites could be uses for high-performance electromagnetic interference shielding and as stretchable heaters for wearable thermotherapy. At a 20 wt% PEDOT:PSS loading, the composite films show a conductivity of 77 S cm-1 and an elongation at break of about 32.5% and this stretchable conductive film exhibits a high electromagnetic interference shielding effectiveness (SE) of about 62 dB over the X-band frequency range at a film thickness of only 0.15 mm. Through incorporation 1wt% reduced graphene oxide in to the 5wt% PEDOT:PSS/WPU film, the stretchable conductive film shows uniformly and stable heating behaviour under the repetitive voltage on/off cycles, and the temperature remains almost unchanged under a tensile strain of up to 30% which can be used in the wearable and long-term thermotherapy applications.

2:15pm - 2:30pm

A Simple Way to Fabricate Controllable Ultra-Fine Metal Patterns on Flexible Polymer Substrates

Tao ZHANG, Linda Y.L. WU, Zhenfeng WANG

Singapore Institute of Manufacturing Technology, Agency for Science, Technology and Research (A*STAR), Singapore

The booming of multifunctional electronic devices which are wearable, bendable, stretchable, and compressible generates numbers of new products for applications such as point-of-care microfluidic devices, wearable sensors, biomedical actuators, and flexible displays, etc. An important step in manufacturing those fascinating devices is fabricating reliable conductive connectors or electrodes within reasonable cost. In the past two decades, various approaches have been published in order to address this issue, in which materials such as metal, carbon nanotube, graphene, conductive polymers, and nanowires have been employed into flexible substrates. Due to low cost and stability, metal such as copper is still the first choice for preparation of conductive tracks. In this research, a simple and low cost method was proposed for fabrication of controllable fine copper features ranging from 10 to few hundred micrometers on flexible polymer substrate with good adhesive strength. In our approach, a functional layer of polymers which can assist the electroless plating of copper is chemically grafted on flexible polymer substrates by plasma and UV induced surface grafting polymerization. The polymer grafted layer can be patterned via a photo mask placed between the monomer solution and the UV light source. The finest feature on thermoplastic substrates in this research was 10 micrometers with good resolution. In addition, a scale-up prototype for mass production of substrates with patterned assisting polymer grafted layer was designed and demonstrated. Compare with published methods such as soft lithography, inkjet printing, or chemical vapor deposition, our method provides outstanding advantages such as smaller features, higher adhesive strength with substrates, lower cost, and scalable for large areas.

2:30pm - 3:00pm

Wearable Electronics and Sensors for Bio-medical Applications

Chengkuo LEE1,2,3, Hao WANG1,2,3

1Department of Electrical and Computer Engineering, National University of Singapore, Singapore; 2Center for Sensors and MEMS, National University of Singapore, Singapore; 3National University of Singapore Suzhou Research Institute (NUSRI), China

Wearable medical devices based on flexible electronics have received major attention recently owing to their considerable practicability for several applications. By leveraging the MEMs technology and flexible materials fabrication processes, we developed various functional devices aiming different medical applications. Technology for enabling drug delivery with precise control is strongly demanded by patients with diabetes or other chronic diseases. More intelligent functions in controllable manner without requiring electrical power will make low-cost drug delivery patches come true. One of the promising candidates is triboelectric technology which has been deployed as nanogenerators and self-powered glucose sensors recently. A smart microneedle patch is developed with the integration of microneedle patch and TENGs for a volume controlled drug delivery triggered by finger pressing. Leveraging triboelectric materials and compatible fabrication technology, we successfully develop a self-powered flexible skin patch for transdermal insulin delivery with novel liquid volume sensor to monitor delivered drug volume and flexible energy harvester using the same triboelectric mechanism. Meanwhile, by optimizing the material and structure, a very unique bendable microneedle design of two kinds of configurations, with bio-dissolvable and non bio-dissolvable sharp tips, is developed. These bendable microneedles can keep intact after skin penetration when a lateral movement between the microneedle and skin surface, which is induced by friction in real applications, occurs. The developed flexible skin patch for transdermal drug delivery is further validated by in vivo experiments in rats. We also explore the feasibility of direct neural stimulation by the output signal from TENGs. With a unique design of water/air triboelectric nanogenerator(WATENG), the charge transfer during the operation of WATENG can be amplified to direct stimulate tibial nerve and peroneal nerve and induce plantar flexion and ankle dorflexion. Meanwhile, the WATENG connected with a sling electrode wrapped around the sciatic nerve can also realize a selective stimulation.

3:00pm - 3:15pm

Developing Flexible Conductive Interconnects with Liquid Metal films

Yiwei LIU, Qin QIN, Chunlei ZHENG, Run-Wei LI

Ningbo Institute of Materials Technology and Engineering (NIMTE), Chinese Academy of Sciences (CAS), China

In recent years, with the rapid development of flexible electronics, flexible circuits, flexible displays, flexible sensors, flexible storages and other flexible electronic devices have received more and more attention, which are triggering a revolution in electronic technology. In particular, flexible conductive interconnects are the key for connecting the flexible electronic devices. Liquid metal is in a liquid state at room temperature with high deformation ability and conductivity, which is one of the good candidates for developing the flexible conductive interconnects. Moreover, with miniaturization of the devices, the flexible conductive interconnects are inclined to be thinner to match the micro- or nano- devices. Here, we present the approachs for fabricating nanoscale to microscale liquid metal films. Our results show that the liquid metal films are packed by core-shell structured liquid metal droplets. Flexible conductive interconnects can be obtained by mechanical sintering. Flexible designed circuits are also demonstrated using this method. The results suggest new ways for the flexible conductive interconnects.

3:15pm - 3:30pm

Elastic Electrode with Highly Dynamic Stability and Electrical Conductivity

Jie SHANG, Run-Wei LI

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, China

Elastic electrode plays a significant role in the wearable electronics, which is an indispensable component. The existing elastic electrodes, which are prepared through doping solid-state conductive materials in elastic matrix, not only have poor conductivity but also bad stability so their application range is restricted. In this paper, liquid metals with better conductivity and deformation have been selected as conductive fillers to prepare elastic electrodes. Liquid-metal electrode has excellent conductivity (square resistance: 0.018 Ω/□, electrical conductivity: 5.26×103 S·cm-1) and dynamic stability (60% strain @ ΔR/R0~1%, traditional elastic electrodes: 60% strain @ ΔR/R0~1000-1000000%) and has shown a wide applied prospect in different domain.

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