Nanogenerators in Korea

Fossil fuels leaded the 21st century industrial revolution but caused some critical problems such as exhaustion of resources and global warming. Also, current power plants require too much high cost and long time for establishment and facilities to provide electricity. Thus, developing new power production systems with environmental friendliness and low-cost is critical global needs. There are some emerging energy harvesting technologies such as thermoelectric, piezoelectric, and triboelectric nanogenerators, which have great advantages on eco-friendly low-cost materials, simple fabrication, and various operating sources. Since the introduction of various energy harvesting technologies, many novel designs and applications as power suppliers and physical sensors in the world have been demonstrated based on their unique advantages. In this Special Issue, we would like to address and share basic approaches, new designs, and industrial applications related to thermoelectric, piezoelectric, and triboelectric devices which are on-going in Korea. With this Special Issue, we aim to promote fundamental understanding and to find novel ways to achieve industrial product manufacturing for energy harvesters

Aerosol-Jet Printed Nanocomposites for Flexible and Stretchable Thermoelectric Generators

Converting waste heat from the environment into usable electricity, via thermoelectric generators (TEGs) based on thermoelectric (TE) materials, is predicted to be one of the most promising renewable energy solutions of the future. TE materials produce a current when subjected to a temperature gradient as a result of the Seebeck effect, and are characterised by a TE figure of merit, ZT = S2σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the operating temperature, and κ is the thermal conductivity. TEGs can be used as an energy source for ‘small-power’ applications, such as wireless sensors and wearable devices. Nonetheless, traditional inorganic TE materials pose significant challenges owing to their high cost, toxicity, scarcity, and brittleness, particularly when it comes to applications requiring flexibility and/or stretchability. On the other hand, organic TE polymers are less expensive, environmentally friendly, and flexible. However, they typically suffer from poor TE performance due to their comparatively low S and σ. This thesis therefore seeks to explore solutions for high-performance and mechanically conformable TEGs based on organic-inorganic TE nanocomposites, adopting a material engineering approach to enhancing TE properties while ensuring the flexibility and/or stretchability of TEGs. In this work, a flexible and robust TEG based on a novel hybrid nanocomposite structure for harvesting energy from low-grade waste heat, has been successfully fabricated via a customised and scalable aerosol-jet printing (AJP) technique. Firstly, Bi2Te3 nanoparticles and Sb2Te3 nanoflakes were fabricated using a solvothermal synthesis approach, and their resulting morphological and microstructural properties were studied. They were then incorporated into a conducting polymer matrix poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) via the AJP method, resulting in well-dispersed TE nanocomposites on flexible polyimide substrates. These TE nanocomposites comprised Bi2Te3/Sb2Te3 nano-inclusions with higher S and σ embedded within a polymeric PEDOT:PSS matrix having lower κ. The compositions were dynamically tuned and controlled by the in-house developed in situ mixing method to optimise the resulting power factor (PF = S2σ). The AJP technique used in this work allows functional materials to be printed from inks with a wide range of viscosities and constituent particle sizes and shapes. The morphological and TE properties of AJ-printed nanocomposite structures were then evaluated as a function of the composition so that optimum ink formulation and printing conditions could be found to maximise the final TE performance. Importantly, these TE nanocomposites were found to be particularly stable and robust upon repeated flexing. They can be directly integrated into high-performance TEGs with minimal post-possessing treatment, making them particularly suitable for flexible TE applications. Subsequently, multiwall carbon nanotubes (MWCNTs) were introduced to enhance σ of AJ-printed nanocomposites, thereby achieving even higher PF values. A novel in situ mixing method was capable of simultaneously incorporating high-S Sb2Te3 nanoflakes and high-σ MWCNTs that could provide good inter-particle connectivity, to significantly enhance the TE performance of PEDOT:PSS. Rigorous flexing and fatigue tests also confirmed the excellent mechanical robustness and stability of these AJ-printed MWCNTs-based TE nanocomposites. The added MWCNTs have led to not only higher σ, but they also have improved the mechanical flexibility and fatigue robustness of the resulting nanocomposites. Since the ZT and PF of TE materials often have a strong dependence on temperature, a single TE material spanning a given temperature range is unlikely to have an optimal ZT or PF across the entire range, leading to the inefficient TEG performance. The temperature-dependent TE properties of AJ-printed TE nanocomposites were therefore studied as a function of the loading fraction, with a view to enhancing the overall TE performance of a TEG by varying its composition accordingly across a given temperature range. For the first time, compositionally graded thermoelectric composites (CG-TECs) have been developed and shown to improve TE performance over TEGs having a single composition across the same temperature range. The composition of the TE nanocomposite was systematically tuned along the length of the TEG in order to optimise the PF along the temperature gradient between which it operates. Lastly, the AJP technique was used to fabricate free-standing and stretchable TE structures, by printing serpentine patterns of the TE ink onto a sacrificial substrate that was subsequently removed. The TE performance and stretchability under different imposed mechanical conditions were evaluated, including testing for the reliability of prolonged stretching cycles. The CG-TEC concept was also incorporated into the stretchable structure to achieve further improvement of TE performance.China Scholarship Council and Cambridge Commonwealth, European and International Trus

Research on Powering a Personal Heating Garment with a Hybrid Power Supply

Due to the extensive contribution of the fossil fuels’ combustion to the global warming, increasing attention has been drawn to reduce the carbon footprint of all sectors by moving toward green technologies. Accordingly, personal comfort systems (PCSs) are considered as a green substitute for the conventional heating, ventilation, and air conditioning (HVAC) systems in the buildings. Precisely, PCSs can address the thermal comfort of each individual in shared spaces, such as office buildings, with remarkably lower energy consumption than the HVAC systems. To clarify, they save energy by conditioning only the air surrounding each individual, leaving the unoccupied points of the buildings unconditioned. However, their main drawback is that they are mostly powered either by a fossil fuel based power supply (i.e. public electricity) or batteries, which to some extent offsets their eco-friendly feature. Regarding batteries, although they are not considered as a fossil fuel based power supply, they can cause negative environmental impact due to their constitutive elements (e.g. cobalt). Accordingly, in this thesis, it was proposed to develop a hybrid power supply comprising a renewable power source called a thermoelectric generator (TEG) and a rechargeable battery to reduce the carbon footprint of the PCSs. To illustrate, a TEG is considered as a promising thermal energy harvester, which captures the waste ambient heat and converts it into electricity. To put it another way, it employs the temperature difference between a hot and a cold object to generate electricity. In this research, this temperature difference was provided by a candle and the ambient air as the heat and cold sources, respectively. The main reason for using a candle as the heat source was that at room temperature none of the existing internal heat sources (e.g. radiators, hot pipe works) could provide the required temperature difference along the thermoelectric (TE) legs. As a result, the TE legs could not generate enough electricity to power a PCS. Regarding the rechargeable battery, it mainly served as a storage system to store the generated electricity by the TEG to release it on demand. In fact, this storage system performed a pivotal role between the TEG (as a green energy supply) and the electricity demand. To clarify, the generated electricity by a TEG is variable, depending on the temperature difference along its legs. Thus, to provide a reliable power for the studied PCS, usage of a storage system was inevitable. In addition, due to the low output current of the TEGs at the room temperature, the storage system also performed as a backup power supply to provide a constant current for the PCS. To develop the TEG part of the hybrid power supply, initially the life cycle impact of 14 thermoelectric materials were numerically studied from cradle to gate (i.e. raw material’s extraction to manufacturing the final material). The main aim of this numerical study was to select the most environmental friendly material out of the three TE types of inorganic, organic, and hybrid. The employed software for this life cycle impact assessment (LCIA) was GaBi v.4.4, and the results proved the greatest environmental damage of the inorganic type compared with the other two types. However, Bi2Te3 was an exceptional inorganic TE material that its life cycle impact was not only less than that of the other studied inorganic TE materials, but also far less than that of the studied organic and hybrid ones. According, an off-the-shelf TEG consisted of Bi2Te3 was selected for this research, and different integrating patterns were determined to couple six of that together. These patterns were considered based on providing enough temperature difference along the TE legs. Accordingly, three different patterns were developed namely, coating either the top half, or the bottom half, or fully the legs with the integrating substrate. To further improve the temperature difference along the legs, the thermal conductivity of the integrating substrate was manipulated by adding different fillers to it. Then, the thermoelectric effects of all of the developed samples were studied both numerically (i.e. computational modelling by COMSOL) and experimentally (i.e. laboratory tests). Based on the outcomes of both studies, coating only the top half of the legs with a low thermal conductivity substrate called polydimethylsiloxane (PDMS) resulted in the highest output power compared with the other two patterns. Accordingly, the TEG part of the hybrid power supply was fabricated with respect to the achieved optimal integrating substrate. Then, to further improve the temperature difference along the TE legs, two different heatsinks (pin-shaped and bumpy-shaped) were developed, and their performances were studied in the laboratory under three air flow conditions (0,1.2, and 2.4 m/s). The results proved the superiority of the pin-shaped heatsink to the bumpy-shaped one after being attached to the PDMS-based integrating substrate. Next, six of the considered off-the-shelf TEG were coupled together from the top half of their legs using the optimal developed PDMS-based integrating substrate. After that, the pre-developed pin-shaped heatsink was attached to the integrating substrate. Then, the integrated TEGs were coupled with a rechargeable battery to heat a pair of pre-developed heating armbands (i.e. the studied PCS). To test the heating performance of the armbands, they were tested in-field on eight subjects served as office workers in the heating season of March in the UK. The results revealed that at roughly 15 °C to 16 °C ambient temperature, 75% of the subjects felt warmer after 30 min of wearing the armbands. To specify, the armbands improved their average comfort level from slightly uncomfortable to slightly comfortable after 30 min of wearing them. Thus, not only this thesis developed a PCS concerning its conditioning performance, but also it addressed the sustainability aspect of its power supply. Accordingly, this thesis paves the way for further research on developing different types of renewable power supplies for any green technologies, including PCSs

Stretchable Piezoelectric Power Generators Based on ZnO Thin Films on Elastic Substrates

The paper describes a stretchable, microfabricated power generator that will be attached on the skin and will produce energy based on the movements of the human body. The device was fabricated on a polymeric, elastomeric, poly(dimethylsiloxane) (PDMS) sheet. It consists of a piezoelectric thin film of ZnO sandwiched between two stretchable gold electrodes. An innovative technique was used for the deposition of ZnO thin film on the gold electrode-coated polymeric substrate at low temperatures below 150C. This is the first attempt to use a uniform film of ZnO, for energy harvesting. The ZnO film had the thickness at the submicron scale and the surface at the centimeter scale. We demonstrated that under a strain of 8% the voltage output from this power generator was equal to 2 V, the power output was equal to 160 W and the corresponding power density was 1.27 mW/cm2. This device has great potential for application in power sensors attached on the human body, such as temperature sensors or wearable electrocardiography systems

웨어러블 센서 및 에너지 소자의 공간 신호 및 열 전달 증진을 위한 나노복합체를 이용한 기계적 순응성 향상

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 홍용택.Electronic skin (e-skin) that mimics mechanical and functional properties of human skin has a strong impact on the field of wearable electronics. Beyond being just wearable, e-skin seamlessly interfaces human, machine, and environment by perfectly adhering to soft and time-dynamic three-dimensional (3D) geometries of human skin and organs. Real-time and intimate access to the sources of physical and biological signals can be achieved by adopting soft or flexible electronic sensors that can detect pressure, strain, temperature, and chemical substances. Such extensions in accessible signals drastically accelerate the growth of the Internet of Things (IoT) and expand its application to health monitoring, medical implants, and novel human-machine interfaces. In wearable sensors and energy devices, which are essential building blocks for skin-like functionalities and self-power generation in e-skin, spatial signals and heat are transferred from time-dynamic 3D environments through numerous geometries and electrical devices. Therefore, the transfer of high-fidelity signals or a large amount of heat is of great importance in these devices. The mechanical conformability potentially enhances the signal/heat transfer by providing conformal geometries with the 3D sources. However, while the relation between system conformability and electrical signals has been widely investigated, studies on its effect on the transfer of other mechanical signals and heat remain in their early stages. Furthermore, because active materials and their designs for sensors and energy devices have been optimized to maximize their performances, it is challenging to develop ultrathin or soft forms of active layers without compromising their performances. Therefore, many devices in these fields suffer from poor spatial signal/heat transfer due to limited conformability. In this dissertation, to ultimately augment the functionalities of wearable sensors and energy devices, comprehensive studies on conformability enhancement via composite materials and its effect on signal/heat transfer, especially in pressure sensors and thermoelectric generators (TEGs), are conducted. A solution for each device is carefully optimized to reinforce its conformability, taking account of the structure, characteristics, and potential advantages of the device. As a result, the mechanical conformability of each device is significantly enhanced, improving signal/heat transfer and consequently augmenting its functionalities, which have been considered as tough challenges in each area. The effect of the superior conformability on signal/heat transfer is systematically analyzed via a series of experiments and finite element analyses. Demonstrations of practical wearable electronics show the feasibility of the proposed strategies. For wearable pressure sensors, ultrathin piezoresistive layers are developed using cellulose/nanowire nanocomposites (CNNs). The unique nanostructured surface enables unprecedentedly high sensor performances such as ultrahigh sensitivity, wide working range, and fast response time without microstructures in sensing layers. Because the ultrathin pressure sensor perfectly conforms to 3D contact objects, it transfers pressure distribution into conductivity distribution with high spatial fidelity. When integrated with a quantum dot-based electroluminescent film, the transferred high-resolution pressure distribution is directly visualized without the need for pixel structures. The electroluminescent skin enables real-time smart touch interfaces that can identify the user as well as touch force and location. For high-performance wearable TEGs, an intrinsically soft heat transfer and electrical interconnection platform (SHEP) is developed. The SHEP comprises AgNW random networks for intrinsically stretchable electrodes and magnetically self-assembled metal particles for soft thermal conductors (STCs). The stretchable electrodes lower the flexural rigidity, and the STCs enhance the heat exchange capability of the soft platform, maintaining its softness. As a result, a compliant TEG with SHEPs forms unprecedentedly conformal contact with 3D heat sources, thereby enhancing the heat transfer to the TE legs. This results in significant improvement in thermal energy harvesting on 3D surfaces. Self-powered wearable warning systems indicating an abrupt temperature increase with light-emitting alarms are demonstrated to show the feasibility of this strategy. This study provides a systematic and comprehensive framework for enhancing mechanical conformability of e-skin and consequently improving the transfer of spatial signals and energy from time-dynamic and complex 3D surfaces. The framework can be universally applied to other fields in wearable electronics that require improvement in signal/energy transfer through conformal contact with 3D surfaces. The materials, manufacturing methods, and devices introduced in this dissertation will be actively exploited in practical and futuristic applications of wearable electronics such as skin-attachable advanced user interfaces, implantable bio-imaging systems, nervous systems in soft robotics, and self-powered artificial tactile systems.인간 피부의 기계적 특성 및 기능을 모방하는 전자피부(electronic skin, e-skin)는 웨어러블 전자기기 분야의 트렌드를 바꾸고 있다. 기존의 웨어러블 전자기기가 단지 착용하는데 그쳤다면, 전자피부는 인간의 피부와 장기 표면에 완벽하게 붙어 동작함으로써 기존에는 접근 불가능 했던 다양한 생체 신호를 높은 신뢰도로 감지하고 처리할 수 있다. 실시간으로 감지 가능한 생체 신호의 확장은 사물인터넷(Internet of Things, IoT)의 성장을 획기적으로 가속화하고 헬스케어, 의료용 임플란트, 소프트 로봇 및 새로운 휴먼 머신 인터페이스로의 응용을 가능하게 한다. 전자피부의 필수요소인 센서와 에너지 소자에서는 삼차원 표면의 공간신호와 열에너지를 손실 없이 전달하는 것이 매우 중요하다. 이러한 공간 신호와 열에너지는 다양한 기하 구조와 전자소자를 거쳐 처리 가능한 신호로 전달된다. 이 과정에서 3차원 표면에 빈틈없이 붙는 기계적 순응성(mechanical conformability)은 공간신호와 열에너지를 왜곡 없이 전달하는 것을 가능하게 한다. 전자피부의 기계적 순응성을 증가시키는 방법은 크게 다음과 같이 두 가지로 나눌 수 있다. (1) 전자피부를 두께를 낮추는 전략과 (2) 전자피부의 영률(Youngs modulus)을 낮추어 고무와 같이 부드럽게 만드는 전략이다. 하지만, 기존 센서 및 에너지 소자를 위한 재료와 디자인이 각 장치의 성능을 향상시키는 것에 초점이 맞추어져 있기 때문에, 고성능을 유지하면서 매우 얇거나 연질 형태의 소자를 개발하는 것은 매우 도전적이었다. 따라서 고유연성을 확보하지 못한 기존 센서와 에너지 소자는 공간 신호 및 열 전달이 심각하게 저해되고, 이로 인해 공간 압력의 왜곡, 열전 효율의 저하와 같은 한계를 보여준다. 이 논문에서는 웨어러블 센서와 에너지 소자의 비약적인 기능 향상을 궁극적인 목표로, 각 소자에 최적화된 재료와 제작방식, 구조를 이용해 이들의 기계적 순응성을 획기적으로 높이고, 이를 통한 공간 신호 및 열 전달의 향상을 심도 있게 분석한다. 특히, 두께를 낮추거나 영률을 낮추는 두 가지 전략 중 각 소자에 가장 적합한 전략을 선택하고, 체계적인 방법론을 적용하여 이들의 기계적 순응성과 공간 신호 및 열 전달을 증진시킨다. 이 과정에서 나노융복합재료가 각 전략을 구현하는 핵심 요소로 작용한다. 각 소자에 따른 구체적인 연구 내용은 다음과 같다. 첫째, 압력 센서의 경우 초박막 셀룰로오스/나노와이어 복합체를 이용하여 고성능의 저항방식 압력 센서를 개발한다. 이러한 복합체는 표면에 형성된 고유한 나노구조 덕분에 마이크로구조체를 이용한 기존 압력 센서보다 월등한 성능을 보여준다. 특히, 1 마이크로 미터 수준의 매우 얇은 두께로 인해 접촉 물체의 복잡한 형상에 완벽하게 순응할 수 있고, 이로 인해 고해상도 압력 분포를 왜곡 없이 저항 분포로 전달할 수 있다. 이러한 압력 센서를 양자 점 발광소자와 결합하여 고해상도의 압력분포를 높은 정밀도로 이미징 가능한 발광 소자를 보고한다. 둘째, 열전 소자의 경우 기존의 금속 전극으로 인한 낮은 유연성과 탄성중합체의 낮은 열 전도도를 극복하기 위해 열 전달 능력이 획기적으로 향상된 낮은 영률의 소프트 전극 플랫폼을 개발한다. 소프트 플랫폼은 내부에 은 나노와이어 기반의 신축성 전극을 갖고 있으며, 자기장을 통해 자가 정렬된 금속 입자들이 효과적으로 외부 열을 열전 재료에 전달한다. 이를 기반으로 제작된 고유연성 열전 소자는 삼차원 열원에 빈틈없이 붙어 열 손실을 최소화 하며, 이로 인해 높은 열전 효율을 달성한다. 이 논문은 다양한 전자소자의 유연성을 증진시키고 이를 통한 공간 신호 및 열 전달의 향상을 도모하고 분석하는 체계적이고 종합적인 방법론을 제시했다는 데 큰 의의가 있다. 제안된 방법론은 분야에 국한되지 않고 다양한 소자의 개발에 적용할 수 있어 웨어러블 기기와 전자피부 분야의 기계적, 기능적 발전에 크게 기여할 것으로 기대된다. 뿐만 아니라 이 연구에서 최초로 개발한 소재 및 소자들은 다양한 웨어러블 어플리케이션과 산업에 곧바로 융합되고 응용될 수 있다. 이를 통해 신체 부착 및 삽입 가능한 생체 이미징 시스템, 소프트 로봇을 위한 신경 체계, 자가 발전이 가능한 인공 감각 기관, 가상 및 증강 현실을 위한 새로운 유저 인터페이스와 같은 미래 지향적 융합 어플리케이션의 실현을 앞당길 것으로 기대된다.Chapter 1. Introduction 1 1.1 Wearable Electronics and Electronic Skin 1 1.2 Mechanical Conformability of Electronic Skin 6 1.2.1 Definition and Advantages 6 1.2.2 Thickness-Based Conformability 11 1.2.3 Softness-Based Conformability 15 1.3 Conformability for Enhanced Signal/Heat Transfer in Wearable Sensors and Energy Devices 19 1.3.1 Conformability for Spatial Signal Transfer in Pressure Sensors 20 1.3.2 Conformability for Heat Transfer in Thermoelectric Generators 22 1.4 Motivation and Organization of This Dissertation 24 Chapter 2. Ultrathin Cellulose Nanocomposites for High-Performance Piezoresistive Pressure Sensors 28 2.1 Introduction 28 2.2 Experimental Section 31 2.2.1 Fabrication of the CNNs and Pressure Sensors 31 2.2.2 Measurements 34 2.3 Results and Discussion 38 2.3.1 Morphology of CNNs 38 2.3.2 Piezoresistive Characteristics of CNNs 41 2.3.3 Mechanism of High Sensitivity and Great Linearity 45 2.3.4 Fast Response Time of CNN-Based Pressure Sensors 49 2.3.5 Cyclic Reliability of CNN-Based Pressure Sensors 53 2.3.6 Mechanical Reliability and Conformability 57 2.3.7 Temperature and Humidity Tolerance 63 2.4 Conclusion 66 Chapter 3. Ultraflexible Electroluminescent Skin for High-Resolution Imaging of Pressure Distribution 67 3.1 Introduction 67 3.2 Main Concept 70 3.3 Experimental Section 72 3.3.1 Fabrication of Pressure-Sensitive Photonic Skin 72 3.3.2 Characterization of Photonic Skin 74 3.4 Results and Discussion 76 3.4.1 Structure and Morphology of Photonic Skin 76 3.4.2 Pressure Response of Photonic Skin 79 3.4.3 Effect of Conformability on Spatial Resolution 85 3.4.4 Demonstration of High-Resolution Pressure Imaging 99 3.4.5 Pressure Data Acquisition 104 3.4.6 Application to Smart Touch Interfaces 106 3.5 Conclusion 109 Chapter 4. Intrinsically Soft Heat Transfer and Electrical Interconnection Platforms Using Magnetic Nanocomposites 110 4.1 Introduction 110 4.2 Experimental Section 115 4.2.1 Fabrication of SHEPs 115 4.2.2 Measurements 117 4.3 Results and Discussion 119 4.3.1 Fabrication Scheme and Morphology of SHEPs 119 4.3.2 Calculation of Particle Concentration in STCs 124 4.3.3 Enhancement of Heat Transfer Ability via Magnetic Self-Assembly 127 4.3.4 Softness of STCs 131 4.3.5 Mechanical Reliability of Stretchable Electrodes 133 4.3.6 Optimization of Magnetic Self-Assembly Process 135 4.4 Conclusion 139 Chapter 5. Highly Conformable Thermoelectric Generators with Enhanced Heat Transfer Ability 140 5.1 Introduction 140 5.2 Experimental Section 142 5.2.1 Fabrication of Compliant TEGs 142 5.2.2 Measurements 144 5.2.3 Finite Element Analysis 147 5.3 Results and Discussion 149 5.3.1 Enhancement of TE Performance via STCs 149 5.3.2 Mechanical Reliability of Compliant TEGs 157 5.3.3 Enhanced TE Performance on 3D Surfaces via Conformability 162 5.3.4 Self-Powered Wearable Applications 167 5.4 Conclusion 171 Chapter 6. Summary, Limitations, and Recommendations for Future Researches 172 6.1 Summary and Conclusion 172 6.2 Limitations and Recommendations 176 6.2.1 Pressure Sensors and Photonic Skin 176 6.2.2 Compliant TEGs 177 Bibliography 178 Publication List 186 Abstract in Korean 192Docto

블록공중합체의 나노 구조 제어를 통하여 나노 패턴된 이차원 물질의 열전 성능 극대화에 대한 연구

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 화학생물공학부, 2018. 8. 이종찬.This study presents fabrication and characterization of nano patterned low dimensional materials fabricated from block copolymer (BCP) self-assembly and nano lithography and application to the thermoelectrics. Also the thermoelectric generator from conductive polymer and rubbery BCP is prepared and applied to the self-powered devices. Firstly, universal method to prepare perpendicular BCP nanopattern is introduced. Universal solution for 3 different BCP including polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), polystyrene-b-polydimethylsiloxane (PS-b-PDMS) and polystyrene-b-poly(2-vinylprydine) (PS-b-P2VP) is adopted to produce perpendicular micro domain. Short time plasma treatment was applied to the top surface of BCP which initiate the crosslinking reaction to produce crosslinking layer. The crosslinking layer exhibits physical immobilization effect to both BCP blocks. The crosslinking layer also applied to the bottom layer replacing random copolymer brush, and the bottom layer can act as a neutral layer to the BCP film. The perpendicular nanopattern from 3 different BCP was observed with scanning electron microscope (SEM) and grazing intensity small angle x-ray scattering (GI-SAXS). BCP with plasma treatment of both top and bottom has fully-perpendicular orientation from the bottom to the top. The crosslinking layer on the top surface is more stiff than neat BCP, the wrinkle is induced after annealing process. In this reason, the thickness of crosslinking layer is controlled by varying the intensity and time of plasma treatment. Secondary, graphene nano structure was fabricated from BCP self-assembly. The large graphene up to 2 centimeter scale was fabricated from chemical vapor deposition (CVD) and nano patterned using PS-b-P2VP sphere nanopattern. Thermoelectric properties of the graphene nanomesh structure with controlled neck width is enhanced up to 40 times higher than pristine graphene. The Seebeck coefficient of the bilayer graphene nanomesh with 8 nm neck width shows the highest value of ~ 520 μV/K among the graphene-related materials. The thermal conductivity of suspended graphene nanomesh is reduced to ~78 W/m·K which is the lowest thermal conductivity for graphene nanostructure. Classical and quantum mechanical calculations supported my nanomesh approach, which can achieve high thermal properties based on reduced thermal conductivity and higher thermopower due to the confined geometry. Also the heterostructure of graphene nanostructure and transition metal dicalcogenides was introduced. Molybdenum disulfide (MoS2) has extremely high Seebeck coefficient and low thermal conductivity, however, very low electrical conductivity. To enhance the electrical conductivity selectively, graphene nanoribbon is adopted as an electron highways to the MoS2 thin film. The large area graphene nanoribbon was fabrication from block copolymer lithography, and was transferred to the MoS2 atomic layer. The graphene nanostructure significantly enhances the electrical conductivity of the MoS2 atomic layer more than 1000 time higher. We show that with heterostructure, the thermoelectric properties can be enhanced. Finally, PEDOT:PSS with coaxial strut was introduced for thermoelectric generator applications. The increment of the data communication between machine to machine, machine to human and human to human leads the requirement of collecting data from any kinds of sensors. One of the most important sensor is pressure sensor which can give information of blood pressure, heat beating rate or something. And the electric energy source is required to these kinds of electric devices, and the energy source is also needed to be flexible for the wearable electric devices. Recently, wearable thermoelectric generator based on organic materials are reported and the wearable TEG can generate several microwatt energies. However, to apply these wearable TEG, any kind of electric device should be assembled together with TEG. We introduced coaxial structure for thermoelectric generator. It is found that shell structure of SEBS give the mechanical strength and recovery properties to the foam and PEDOT:PSS is well-known thermoelectric polymer which have moderate thermopower and high electrical conductivity and used to the thermoelectric foam structure for thermoelectric generator. This SPM was assembled to the wearable thermoelectric generator and could generate 338 nW from the forearm.Chapter 1 Introduction 1 1.1 Block Copolymer Self-assembly for Nanolithography ２ 1.2. 2 Dimensional Materials for Thermoelectrics and Size Effect in Low Dimensional Materials ４ 1.3. Motivation ８ 1.4. References １０ Chapter 2 Control of Block Copolymer Nano Domains for Nanolithography 20 2.1. Introduction ２１ 2.2. Experimental ２４ 2.3. Results and Discussion ２７ 2.4. Conclusion ３４ 2.5. References ３５ Chapter 3 Significantly reduced thermal conductivity and enhanced thermoelectric properties of single- and bi-layer graphene nanomeshes with sub-10 nm neck-width 57 3.1. Introduction ５８ 3.2. Experimental ６２ 3.3. Results and Discussion ７５ 3.4. Conclusion ８８ 3.5. References ８９ Chapter 4 Van der Waals Heterostructure of Graphene Nanostructure and Molybdenum Disulfide for Superior Thermoelectric Materials 113 4.1. Introduction １１４ 4.2. Experimental １１７ 4.3. Results and Discussion １２１ 4.4. Conclusion １２４ 4.5. References １２５ Chapter 5 Coaxial Struts and Microfractured Structures of Compressible Thermoelectric Foams for Self-powered Pressure Sensors 143 5.1. Introduction １４４ 5.2. Experimental １４７ 5.3. Results and Discussion １５２ 5.4. Conclusion １６１ 5.5. Refences １６３ Abstract in Korean １８６Docto

Conductive Polymers and Polymer Nanocomposites for Flexible Thermoelectrics.

PhD ThesisWith the development of fields like soft (micro-) robotics, wearable devices and internet-of-things, there is a growing demand for new materials with combinations of functional properties, ranging from electrical conductivity, sensing and energy storage/harvesting, together with mechanical properties like large elastic deformations and toughness. Organic thermoelectric (OTE) materials and their composites are excellent candidates for self-powered sensors, due to their ability to harvest waste heat energy in a robust and reliable manner, combined with mechanical properties (e.g. high strain at break) and additional functionalities. This thesis focuses on the application of OTE as multi-functional self-powered sensors. Three types of representative OTE materials have been mainly investigated to explore different characteristics and potential applications. Three different processing methods have been explored for achieving the different structures aiming at various functions and potential applications in fields like wearable electronics and self-powered sensors. Poly nickel-ethenetetrathiolates (Nax(Ni-ett)n) has been selected as the n-type OTE material. Highly stretchable n-type composite films are obtained by blending with polyurethane. When subjected to a small temperature difference (< 20 oC), the films generated sufficient thermopower to be used for sensing strain and visible light, independently of humidity. Poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has also been selected as the most widely investigated p-type OTE material. A novel self-powered ultrasensitive deformation sensor has been demonstrated based on PEDOT:PSS being Abstract vii coated on Lycra® yarns. By controlling the crack induced patterns of the conductive PEDOT:PSS coating, the strain sensitivity could be tuned in a wide range. Finally, carbon nanotube (CNT) has also been studied. A self-folding method has been used to create 3D structures by fixing CNT veils between patterned polycarbonate and biaxial stretched polystyrene films. The obtained honey-comb shaped OTE device has been utilised as a structural composite as a self-powered integrated sensor

Small-Scale Energy Harvesting from Environment by Triboelectric Nanogenerators

The increasing needs to power trillions of sensors and devices for the Internet of Things require effective technology to harvest small-scale energy from renewable natural resources. As a new energy technology, triboelectric nanogenerators (TENGs) can harvest ambient mechanical energy and convert it into electricity for powering small electronic devices continuously. In this chapter, the fundamental working mechanism and fundamental modes of a TENG will be presented. It can harvest all kinds of mechanical energy, especially at low frequencies, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, moving automobile, flowing water, rain drops, ocean waves, and so on. Such variety of energy harvesting methods promises TENG as a new approach for small-scale energy harvesting

PEDOT : PSS-based conductive textiles and their applications

The conductive polymer complex poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) is the most explored conductive polymer for conductive textiles applications. Since PEDOT:PSS is readily available in water dispersion form, it is convenient for roll-to-roll processing which is compatible with the current textile processing applications. In this work, we have made a comprehensive review on the PEDOT:PSS-based conductive textiles, methods of application onto textiles and their applications. The conductivity of PEDOT:PSS can be enhanced by several orders of magnitude using processing agents. However, neat PEDOT:PSS lacks flexibility and strechability for wearable electronics applications. One way to improve the mechanical flexibility of conductive polymers is making a composite with commodity polymers such as polyurethane which have high flexibility and stretchability. The conductive polymer composites also increase attachment of the conductive polymer to the textile, thereby increasing durability to washing and mechanical actions. Pure PEDOT:PSS conductive fibers have been produced by solution spinning or electrospinning methods. Application of PEDOT:PSS can be carried out by polymerization of the monomer on the fabric, coating/dyeing and printing methods. PEDOT:PSS-based conductive textiles have been used for the development of sensors, actuators, antenna, interconnections, energy harvesting, and storage devices. In this review, the application methods of PEDOT:SS-based conductive polymers in/on to a textile substrate structure and their application thereof are discussed