Conducting Polymers Developed on Ice Surfaces with Enhanced Electrochemical Properties

김경욱 포항공과대학교 일반대학원 2022 국내박사

Conducting polymers have been studied extensively in the past few decades due to various advantages such as high electrical conductivity, optical transparency, chemical stability, flexibility, and low cost. Recently, research to improve the electrical properties of conducting polymers for high performance in electronic devices are intensively conducted. Various studies have been reported to improve the conductivity of conducting polymers by controlling various factors such as the type of dopant, doping level, and conjugate length in the synthesis of conducting polymers. More recently, improving conductivity through the formation of nanostructure of conducting polymers has been attracted great attention. In order to synthesize conducting polymer nanostructures, various methods using hard templates and soft templates as well as conventional chemical oxidation polymerization have been reported. In particular, among them, the two-dimensional nanostructure has become important because it is advantageous for high-density integration of next-generation electronic devices to exhibit improved electron transport properties. Nevertheless, the synthesis of conducting polymers having two-dimensional nanostructure with high electrical conductivity have mainly based on methods using graphene oxide as templates. However, this approach showed difficulty in removing the template after synthesis, which made hard to obtain pure conducting polymer. It was also difficult to obtain reliable electrical properties over a large area due to the non-uniform distribution of functional groups of graphene oxide. To overcome this limitation, I synthesized conducting polymers using the ice surface as a template, where the ice template is easily removed in the next step. Consequently, pure two-dimensional conducting polymer nanosheets with high conductivity were obtained. In this dissertation, the role of crystallinity of the ice surface on the ice-templated conducting polymers are investigated, and new strategies for utilizing the ice-templated conducting polymers as the electrocatalyst, the virus filtration membrane are proposed. Chapter 1 provides an overall overview of ice-assisted chemistry for synthesizing functional materials using ice, and introduces current research trends on conducting polymers prior to introducing ice-templated conducting polymers. Research on conducting polymer-metal composites and porous conducting polymers are also included. Furthermore, research motivation and objectives of this dissertation are presented to develop the current research based on ice-assisted chemistry. Chapter 2 covers the study of the nanostructure and electrical properties of the ice-templated conducting polymers, and the study of a role of the crystallinity of the ice surface. Although the recently established ice-templated synthetic method of two-dimensional conducting polymers is evaluated as an environmentally friendly and easy-fabrication technology, the role of the crystallinity of the underlying ice surface remains unclear in determining the physicochemical and electrical properties of conducting polymers. In this study, crystallinity of ice is systematically controlled, and the electrical properties of conducting polymer nanosheets grown on the ice surface and the packing structure of conducting polymer crystals are studied in depth. Intriguingly, the crystallinity of the conducting polymer nanosheets resembled that of the ice surface, and it was confirmed that the higher the crystallinity of ice, the more predominantly anisotropic growth of the conducting polymer nanosheets in the face-on orientation. In addition, it was turned out that highly crystalline conducting polymer nanosheets led to more efficient charge transport due to improved degree of backbone ordering due to the pre-organized aniline moieties on the ice surface and strong polaron delocalization with the extended chain conformations. These results suggest that controlling the crystallinity of ice is simple but effective to control the electrical properties of conducting polymers. Chapter 3 describes the study of conducting polymer-platinum (Pt) nanoparticle composites based on ice-templated conducting polymers. Pt nanoparticles are well known as the most effective electrocatalysts for various electrochemical reactions. However, for commercially available Pt catalyst supported on carbon such as Pt/C catalyst, a high reaction temperature is generally required. And the particle agglomeration cannot be prevented, so that the catalytic activity decreases rapidly over time. Besides, carbon nanostructures such as graphene are even expensive. Thus, in this study, a new approach for the synthesis of uniform, high areal density Pt nanocrystals supported by ice-templated conducting polymers is presented. The key strategy is the use of ice-templated conducting polymers at the air-water interface as a platform to promote the nucleation of platinum. Highly crystalline Pt nanoparticles with a narrow size distribution of about 2.7 nm and a high electrochemically active surface area of 94.57 m2 g-1 were obtained. It showed good durability and excellent carbon monoxide tolerance. This approach suggests potential applications for the production of various other electrocatalysts with enhanced catalytic activity. Chapter 4 covers the study of the synthesis of two-dimensional porous conducting polymer nanosheets synthesized on the ice surface. In this study, the directional freezing is performed to the microplastics-containing solution and subsequently ice-templated synthesis is conducted on this microplastics-containing ice. This process leads to easy removal of microplastics in aqueous solution by detaching the synthesized conducting polymer nanosheets from the ice. The removal efficiency of microplastics was over 97 %. More importantly, while microplastics are being removed, porous two-dimensional conducting polymer nanosheets are synthesized with a solvent treatment process for removing the microplastics from the detached conducting polymer nanosheets. Intriguingly, the size of the pores could be easily tuned depending on the size of the microplastics. Then, porous conducting polymer nanosheets with 100 nm pores were utilized as the virus filtration membranes for coronavirus (SARS-CoV-2). As a result, high rejection rate up to 96.3 % was achieved. This approach is important in that it can remove microplastics in aqueous solution and simultaneously make porous conducting polymers with various pore sizes, which suggests a potential for variety of applications. Chapter 5 provides conclusions and perspectives based on these studies. Through these studies, the role of ice in ice-templated synthesis was investigated in more depth. 2D nanostructure of the ice-templated conducting polymers could be realized owing to the confinement provided by the quasi-liquid layer (QLL) on the ice surface. It was confirmed that the electrical properties and packing structure of the conducting polymers are greatly affected by the crystallinity of ice surface. Moreover, new advanced nanomaterials with high functionality and improved electrochemical properties were synthesized by utilizing ice-assisted chemistry, which showed high potential for application in various fields. Nevertheless, studies on the utilization of QLL on the ice surface are still lacking, which is ascribed to the difficulty in accurate identification and precise control of QLL. Thus, further studies are required to understand and utilize QLL on the ice surface, which may include the in-situ transmission electron microscopy and ultrafast X-ray scattering experiments. Such future studies will contribute to developing new advanced materials and expanding the scope of the ice-templated synthesis to various applications.

L.v. Beethoven Symphony No.1 in C Major, Op. 21의 분석과 지휘 기법 연구 : 1악장을 중심으로

조부연 창원대학교 2021 국내석사

지휘의 타법 조사연구

서북진 단국대학교 대학원 1993 국내석사

지휘의 역사는 metric한 고전파 이전의 작품에서는 곡의 시작과 끝같은 곳에서 관행적인 지시를 하는데서 시작되었으나 시대의 변화에 따라 악곡의 스코어(score)가 점점 복잡해지고, 방송과 녹음 기술의 발달로 인하여 지난날보다 더욱 원숙한 지휘 기술이 필요하게 되었다. 그동안 지휘에 관한 많은 책들이 출판되었지만 지휘라는 것이 수학적인 수치나 몇 개의 간단한 도식같은 것으로 나타낼 수 있는 것이 아니고 추상적이기 때문에, 어법의 표현이 모두 통일되어 있지 않으며 타법에 있어서도 용어와 용법이 서로 달라 이해 하기가 어려운 실정에 처해있는 것이 사실이다. 논자(論者)는 지휘법 내용중의 타법 이론을 정리해 보고자 국내에 소개된 여러 번역서 중에서 내용이 비교적 풍부하고 타법의 도형과 용법이 많이 기술된 이기홍 번역의 맥스 루돌프(Rudolf, Max)가 지은 "지휘법(The Grammar of Conducting)" 과 우종억 번역의 사이토 히데오(齋藤秀雄)가 지은 "지휘법(指揮法敎程)" 및 정재동 번역의 에밀 칸(Kahn, Emil)이 지은 "지휘법 개설(Conducting)" 등 세권의 저서를 선정하여 타법에서의 점(beating point)의 형성, 속도(tempo) 그리고 리듬(rhythm)을 조사 분석하여 타법이 생성된 이론을 배경으로 타법의 용어, 도형 및 용법등을 분류하여 그 예제를 들어 타법의 실제를 비교 분석하는 방법으로 조사 연구하여 다음과 같은 결론을 얻었다. 첫째, 타법 용어의 우리말 표기와 원어의 내용이 각각 다르게 표현되어 있었고 둘째, 저서에 따라 취급된 내용이 서로 달라서 비교 하기가 어려웠으며 셋째, 용법에 있어서 실습하기에 충분하고 잘 설명된 예제 악보의 부족으로 타법을 이해하며 습득 하기에 어려움이 많다는 것을 깨달았다. 논자(論者)는 타법에 대한 완벽한 이해와 독자적인 기술 습득을 위해 올바르게 해석되어 통일된 타법 용어와 배우기 쉽게 설명된 도형과 용법, 그리고 실제 연주에서 활용될 수 있는 악보의 예를 풍부히 갖춘 "지휘법" 의 연구와 저서의 출판이 시급하다는 것을 제언하였다. The history of conducting started from pointing the start and the end of music prior to classical music. But as time has passed by there has been for a need perfect conducting technology due to the complexity of the score of musical composition and the progress of broadcasting & sound recording technology. For the past years, many works concerned about conducting were published. But because conducting is not expressible by numerical value or simple diagram but abstract, the expression of conducting is not united and terminology and usage are different one another it’s not easy to understand conducting. So, the present writer selected three books, Rudolf Max's "The Grammar of Conducting" translated by Lee Ki Hong, Saito Hideo's "The Correction of Conducting" translated by U Jong Uk and Emil Kahn's "Conducting" translated by Chung Jae Dong which describe conducting on detail and contain the diagram of beating to arrange beating theory. After researching the above three books classified beating terminology, diagram and usage in the background of the theory which describes the occurrence of beating and found out following facts; 1. A diferrence between Korea expression of beating terminology and the contents of original of it. 2. Difficulty in comparing because the contents of the selected books were different one another. 3. Lacking in usage which is enough to practice and scores which explains well. Because of the above three reasons it's not easy to master beating. So the present writer suggested that it is most badly needed to publish those books which contain "the unity of beating terminology", "suitable diagram and usage" and "enough scores" which can be performed and realistic to understand and master beating technique.

(A) reflection type microwave gas sensor with conducting polymer

이용주 Graduate School, Yonsei University 2016 국내석사

In this dissertation, a gas sensor using a reflection type variable attenuator structure with conducting polymer is represented. Modified 90° hybrid coupler structure represents a new design method using conducting polymer as signal line at microwave frequency. For conducting polymer based gas sensor, conducting polymer is used as sensing material to detect the target gas. The adhesion of gas molecules to conducting polymer changes its work function and conductivity. In other words, electrical properties such as permittivity, conductivity, and permeability are changed. Accordingly, the reflection coefficient between polymer and metal signal line will be changed. Therefore, the measured signal at each port will be changed by these electrical characteristics transition. In this dissertation PEDOT:PSS compound is used as sensing material for ethanol gas. In case of PEDOT:PSS, electron movement is occurred by π-orbital bonding which is a typical dual-bonding state between single-bond and double-bond of carbon atoms. Reprocessing procedure by DMSO solvent can enhance conductivity of PEDOT:PSS because of π-orbital bonding strengthened. Due to the movement of electrons emerge quickly, a hydrophobic polaron group of the alcohol gas, ethanol gas molecule for one, molecules are selectively absorbed. Due to high conductivity of PEDOT:PSS sensing material, a partial microstrip line is replaced with conducting polymer instead of the conductor such as copper. Use of conducting polymer as a signal line in microstrip structure has several advantages. First, this method has a simple structure so that it can easily analyze characteristics of conducting polymer when it absorbs target gas. Second, it is possible to realize the fast response time because of skin effect. The reflection type of hybrid coupler structure was selected because to verify the amount of attenuation value changes also the frequency. The experiment environment is maintained the relative humidity 55% ~ 85% and the temperature 23 °C ~ 28°C. 100 ppm, 50 ppm, 30 ppm ethanol gas is flowed into gas sensing device in open environment. Finally, the experiment results indicate that the proposed gas sensor has great response and repeatability. Note that the proposed gas sensor responses to ethanol gas in real-time. In conclusion, the reflection type of gas sensor with conducting polymer can be appropriate to gas sensor at microwave frequency.

소규모 데이터를 활용한 전이 학습 기반 3D 지휘 스타일 동작 생성 연구

오지수 중앙대학교 첨단영상대학원 2024 국내석사

본 논문에서는 소규모 데이터를 활용해 음악 기반 3D 지휘 스타일 동작을 생성하기 위한 새로운 접근 방법을 제안한다. 오디오를 기반으로 3D 동작을 생성하는 연구는 이전부터 꾸준히 진행되어 왔지만 스피치 제스처나 댄스 동작 생성에 한했다. 본 논문에서는 지휘와 같이 특수한 상황에 대한 3D 동작을 생성하고자 했다. 이는 음악 기반 지휘 동작 생성 분야에서 처음으로 시도되는 연구로, 딥러닝 모델 학습에 필요한 데이터가 충분하지 않다는 한계가 있다. 이에 전문 지휘자의 지휘 영상으로부터 음악과 3D 지휘 동작 데이터를 추출해 1.43시간 분량의 소규모 멀티모달 지휘 데이터셋을 새롭게 구축했다. 제한된 학습 데이터로 인한 모델 성능 저하 문제를 해결하기 위해, 대규모 스피치 데이터셋으로 사전 학습된 음성 기반 제스처 생성 모델을 이용한 전이 학습 방법을 고안하였다. 지휘 동작 생성 모델은 음악과 스피치 음성 간의 특징에 대한 차이가 존재하므로 제스처 생성 모델의 오디오 특징 추출 부분을 지휘에 적합하도록 일부 변경하여 구성하였다. 제안한 방법의 효과를 검증하기 위해 사전 학습, 전이 학습 유무 등 학습 단계별 모델의 지휘 동작 생성 결과를 비교했다. 동작의 다양성, 원본과의 유사성, 음악-동작 간의 연관성 등을 평가했으며, 손목 관절 움직임에 대해서는 인체 관절 가동 범위를 고려해 동작의 자연스러움 비교했다. 또한 실제 사람과 유사한 3D 아바타에 생성된 동작을 매핑해 시각적인 비교를 진행했다. 실험 결과 제안된 전이 학습 방법이 대부분의 측면에서 향상된 성능을 보여주었다. 이는 불충분한 데이터의 학습에 제안된 전이 학습을 적용하는 방식이 효과적임을 시사하며, 향후 유사한 동작 생성 연구에 적용될 수 있는 가능성을 제시한다. This paper proposes a novel approach to generate music-driven 3D conducting style motions with small-scale data. Although audio-driven 3D motion generation has been consistently studied, it has been conducted to focus on speech gestures or dance motions. This study aims to generate 3D motions for specific situations like conducting. To the best of our knowledge, no study has been conducted on music-driven 3D conducting motion generation. In order to overcome this challenge, I constructed a new small-scale multimodal conducting dataset containing 1.43 hours by extracting music and 3D conducting motion data from professional conductor videos. I was concerned about degrading the performance of the model due to limited training data, I devised a transfer learning method using a speech-driven gesture generation model pre-trained on a large-scale speech dataset. As music and speech audio features are different, I modified the audio feature extraction part of the gesture generation model to suit conducting on the conducting motion generation model. To validate the proposed method, I compared the conducting motion generation results of models at different training stages, including pre-trained, with and without transfer learning. I evaluated motion diversity, similarity to the original, and music-motion correlation. For wrist joint movements, I compared human-likeness of generated motions considering human joint range of motion. I also conducted visual comparisons by retargeting generated motions to a realistic 3D avatar. Experimental results showed that the proposed transfer learning method demonstrated improved performance in most aspects. This suggests that applying the proposed transfer learning approach is effective and available for learning from insufficient data on the study of motion generation.

바그너(R.Wagner)의 『지휘에 관하여』(1870)의 지휘사적 의의에 관한 고찰 : 19세기 ‘작품에 충실한’(Werktreue) 연주 담론과의 연관성을 중심으로

조민경 서울대학교 대학원 2024 국내석사

본 연구는 리하르트 바그너의 저작 『지휘에 관하여』(Über das Dirigieren, 1870)의 지휘사적 의의를 19세기에 출현한 ‘작품에 충실한’(Werktreue) 연주 담론과의 관계 속에서 고찰한다. 이를 통해 바그너의 지휘론을 심층적으로 탐구하고, 그의 지휘론이 후대의 지휘계에 미친 영향을 비판적으로 평가하기 위한 토대를 마련하고자 한다. 본 연구자는 19세기의 지휘론들이 ‘작품에 충실한’ 연주 담론에 영향을 받은 양상을 살펴보며, 바그너가 『지휘에 관하여』에서 제시한 지휘론이 어떠한 점에서 기존 지휘론들과 차별화되는지 드러내고자 했다. 연구 결과, 『지휘에 관하여』에서 바그너가 충실한 연주의 기준으로 삼은 것은 음악적 텍스트 자체라기보다는, 그 배후에 존재하는 작곡가의 위대한 정신에 가까웠다. 이러한 논리 위에서 바그너는 악보에 기재되지 않은 템포의 뉘앙스를 추가하거나, 오케스트레이션을 수정하여 작곡가의 의도를 더욱 분명히 드러내는 해석의 방식을 제안하였다. 이로써 바그너는 지휘자의 해석을 텍스트의 단순한 재현이 아니라 텍스트의 보완(혹은 텍스트의 올바른 독해)이라는 차원으로 확장해서 이해할 수 있는 토대를 마련하였다. 그의 지휘론은 후대로 계승되며 지휘자들의 연주 해석에 실질적인 영향을 미친 한편으로, 지나치게 자의적인 방법론이라고 비판받기도 했다. 비록 오늘날의 지휘계에 미치는 직접적인 영향력은 20세기에 비해 감소했을지라도, 바그너의 지휘론은 ‘각자의 예술적 비전을 바탕으로 작품을 해석하는 것’을 지휘자의 주된 역할로 인식하는 현대적 관점의 형성에 큰 영향을 미쳤다는 점에서 영속적인 가치를 지닌다. This study delves into the historical significance of Richard Wagner's seminal work, On Conducting (Über das Dirigieren, 1870), exploring its connection with the 'Werktreue' (work-faithfulness) performance discourse prevalent in the 19th century. The objective is to elucidate Wagner's conducting theory in depth and establish a groundwork for a critical assessment of its influence on subsequent conducting practices. This research examines how 19th-century conducting theories were informed and molded by the 'Werktreue' performance ethos, highlighting how Wagner's theories diverged from those predating him and the manifestation of this discourse in On Conducting. Wagner advocated for a performance fidelity that transcended the literal musical text, emphasizing adherence to the composer's profound 'spirit' instead. This perspective shifted the conductor's role from mere reproduction of the text to an interpretive act that seeks to enhance or accurately represent the composer's intentions, thereby introducing a new paradigm in conducting interpretation. While Wagner's conducting theory has impacted interpretations by other conductors and has been critiqued for its subjective leanings, its direct relevance in the contemporary conducting realm appears to have waned since the 20th century. Nonetheless, Wagner's approach has made a lasting contribution to the modern understanding of the conductor's role as primarily one of articulating an artistic vision. This enduring value underscores the significance of Wagner's conducting theory in the broader context of musical interpretation and performance

Design of flexible and transparent electrodes via synthesis of conducting polymers with doping level control

김영노 Graduate School, Yonsei University 2020 국내박사

최근 차세대 유연전자소자에 대한 관심이 급증하면서 이에 따른 투명전극소 재에 대한 연구 또한 활발히 진행되고 있다. 기존의 시장을 장악하고 있는 희 귀금속 기반의 Indium Tin Oxide(ITO) 소재는 자원의 희소성과 가공시 높은 온도의 증착공정을 필요로 하고 금속의 특성상 유연성이나 신축성 측면에서 차세대 유연전자소자에 투명전극소재로서는 부적합한 특성을 보인다. 이에 유 기소재 전도성 고분자 PEDOT:PSS ‘Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)’ 가 대체소재로서 가장 각광받고 있다. PEDOT:PSS는 수분산 형태의 친환경성, 유연성, 용액공정의 간편한 가공성으로 인한 값싼 가격 등 여러가지 장점을 갖지만 전기적 특성에서무기재료를 따라가지 못해 실제 적용이 제한되고 있다. 앞서 많은 선행연구들에서 전도성 고분자의 전기 전도도를 향상시키는 방법에 대해 고안하였고 일부는 정전기 방지나 정공수송 층 소재 같은 분야에서 상업화에 성공하기도 하였다. 하지만 투명전극소재로 적용하기 위해서는 아직까지 전기전도도, 내후성, 투명성 등 해결해야할 문제 들이 남아있다. 본 연구에서는 단분자 형태의 추가 도펀트를 활용한 In-situ 중합을 통해 고전도도, 고투과도를 갖는 PEDOT:PSS를 제조하고 합성후 남아있는 잔여 불순물을 제거할 수 있는 용액상 후처리 공정을 개발하였다. 해당 공정을 통 해 PSS의 제거를 통한 물리적 디도핑과 추가 도펀트 첨가를 통한 화학적 도 핑을 동시에 수행할 수 있어 광투과도와 전기전도도 향상효과를 나타내었다. 또한 단계별 Scale-up 을 통해 180L 이상의 대량생산 공정 적용 가능성을 확인하였고 해당 용액을 이용하여 Roll-to-Roll 대면적 유연 투명전극 필름을 제조하였다. 요즘 이슈화되고 있는 유연 및 신축성 웨어러블 전자소자의 투명전극으로 적용하기 위해 PEGMA와 PSS의 공중합 및 Semi-IPN 구조형성을 통해 soft 한 acid template을 제조하여 자체적으로 연신이 가능한 전도성 고분자 소재 를 개발하였다. 이는 고무 계열의 탄성체와 같이 신축성을 갖지만 절연특성인 기존 소재들과 다르게 신축성과 전도성을 동시에 띄기 때문에 신축성 전자재 료 및 투명전극으로 적용될 수 있다. 본 연구에서 개발한 신축성 투명전극 소 재를 기반으로 연신 전기변색 소자를 개발하였고 해당 연구결과를 통해 향후 ECD를 비롯한 OSC, OLED, OFET, Sensor 등과 같은 투명성과 유연성 및 신 축성을 필요로 하는 전자소자로의 적용가능성을 확인하였다. In recent years, next-generation flexible electronic devices have attracted a considerable scholarly interest, giving rise to an increase in the number of studies on this topic. Although inorganic materials, such as indium tin oxide (ITO), currently dominate the markets, the limitations of such materials include a lack of resources and the requirement of a high-temperature deposition process. In addition, inorganic materials are not suitable for next-generation flexible electronics in terms of flexibility or stretchability due to the nature of inorganic materials. For that reason, the organic conductive polymer, Poly(3,4-ethylenedioxy thiophene):poly(styrenesulfonate) (PEDOT:PSS), is the most popular alternative material. Although the PEDOT:PSS has several advantages, such as being environment-friendly in the form of water dispersion, flexibility, and low cost due to facile solution-process, it is cannot keep up with inorganic materials in terms of the electrical conductivity, and its realistic application is restricted yet. Many previous studies have designed different ways to improve the conductivity of conducting polymers, and some have succeeded in commercializing in areas such as anti-static protection and hole-transport materials. However, in order to apply conducting polymers to transparent electrodes, many issues remain to be solved, such as electrical conductivity, weather stability, and transparency. In the present study, in-situ polymerization with sulfuric acid showed the effect of improved transparency and electrical conductivity through additional doping. The solution-processed filtration was designed with selective control of sulfuric acid and PSS contents. The process of physical de-doping with the removal of the PSS and chemical doping with additional dopants simultaneously improved high transparency and electrical conductivity at thin film. The optimized PEDOT:PSS transparent electrode film showed the figure-of-merit (FoM) value of 99.1 Ω-1 (i.e. two times higher than commercialized PEDOT:PSS). Furthermore, the applicability of mass production was verified by step-by-step scale-up from 1L to over 180L. The large-scale (width 500 mm, length 500 M) organic transparent electrode films were coated on a flexible substrate (PET film) by the roll-to-roll process. Organic conducting polymer PEDOT:PSS is flexible, but it is not intrinsically stretchable. In order to apply the organic transparent electrode materials to the stretchable and wearable electronic devices by incorporating modified acid template with semi-interpenetrating networks (semi-IPN), the soft template acting as an acid dopant was obtained. Finally, the synthesized flexible and stretchable conducting polymer showed superior stretchability and high conductivity. It was then verified as the stretchable electrode material by a fully stretchable electrochromic device.

Conducting Polymer-Based Flexible Transparent Electrode and New Emitting Materials for Organic Light-Emitting Diodes

김만수 경희대학교 대학원 2015 국내박사

Synthesis of semiconducting and conducting metal oxide aerogels for energy and environmental applications

김태희 Graduate School, Yonsei University 2024 국내박사

Aerogel is a material that contains many mesopores, which contribute to its low density, high specific surface area, and low thermal conductivity. Since their incep-tion in 1931 by Stephen Kistler, silica aerogels have served as the primary represen-tation of aerogels. Silica aerogel is extensively utilized as a heat insulating material because of its low thermal conductivity. Additionally, it is being reported that silica aerogel can also be used for sound insulation, as a catalyst and catalyst support, and as a dielectric material. Despite its excellent properties, silica aerogel has limited ap-plications due to its insulating property. Therefore, many researchers focused on the synthesis of non-insulating aerogels with various composition of metal oxides. Nev-ertheless, the synthesis of various metal oxides using traditional metal alkoxide as a precursor shows a difficulty in creating three-dimensional gelation networks, which in turn impact the inherent properties of the materials due to the low reactivity and difficult to control the reaction kinetics. Use of organic epoxide offers a potential solution to overcome these limitations. This dissertation presents three studies that demonstrate the design, synthesis, analysis, and application of advanced semicon-ducting/conducting metal oxide-based aerogels for energy and environmental appli-cations. These aerogels possess high surface area and numerous pores, which con-tribute to their effectiveness in this field. For the semiconducting metal oxide, SnO2 was used as a wide bandgap photocatalyst with the reduced graphene oxide. Also, doping of fluorine to SnO2 reduced its resistivity and applied as a catalytic support to replace the carbon in the field of water electrolysis. In the second study, RuOx based aerogels were synthesized using Ru chloride as a precursor. Ni was doped to RuOx to enhance its electrocatalytic hydrogen evolution reaction (HER) activities. Nickel chloride was used as a doping source, and it was possible to achieve homogeneous doping to RuOx aerogel matrix owing to the high solubility and controlled reaction kinetic of epoxide-initiated sol-gel method. Also, RuOx based aerogels was grown on the surface of Ni foam to be nanostructured RuNi alloy aerogel. As a result, the enhancement in HER activities was achieved. The epoxide-initiated sol-gel method allowed to control the stoichiometry of metal oxide for desired composition. 에어로겔은 많은 meso 기공을 포함하고 있어 낮은 밀도, 높은 비표면적, 낮은 열전도율을 자랑하는 재료이다. 1931년 스티븐 키슬러에 의해 처음 만들어진 이래로, 실리카 에어로겔은 에어로겔의 주된 형태로 인정받아 왔다. 이 실리카 에어로겔은 낮은 열전도율 덕분에 열 절연 재료로 널리 사용되고 있다. 추가적으로, 실리카 에어로겔은 방음 재료로, 촉매와 촉매 지지체로, 그리고 유전체 재료로도 활용될 수 있다고 알려져 있다. 그러나 뛰어난 특성에도 불구하고, 실리카 에어로겔의 활용은 그 절연 특성으로 인해 제한적이다. 따라서 많은 연구자들은 다양한 금속 산화물 조성을 갖는 비절연 에어로겔의 합성에 중점을 두었다. 전통적인 금속 알콕사이드를 전구체로 사용하여 다양한 금속 산화물을 합성하는 과정에서 3 차원 겔화 네트워크를 생성하는 데 어려움이 있으며, 이는 낮은 반응성과 반응 속도를 제어하기 어려움으로 인해 재료의 본래 특성에 영향을 준다. 유기 에폭사이드의 사용은 이러한 한계를 극복할 잠재력을 제공한다. 이 논문은 에너지와 환경 소재로 적용을 위한 반도체/도체 금속 산화물 기반 에어로겔의 설계, 합성, 분석, 그리고 응용을 보여주는 세 가지 연구를 제시한다. 이 에어로겔들은 높은 표면적과 다수의 기공을 가지고 있어, 이 분야에서의 효과성에 기여한다. 반도체 금속 산화물인 SnO2 에어로겔은 큰 밴드갭 광촉매로 사용되었으며, 환원된 그래핀 산화물과 함께 사용되었다. 또한, SnO2에 플루오린을 도핑함으로써 그 저항성을 줄이고, 수전해 분야에서 탄소를 대체할 촉매 지지체로 적용되었다. 두 번째 연구에서는 루테늄 클로라이드를 전구체로 사용하여 RuOx 기반 에어로겔이 합성되었다. Ni가 RuOx에 도핑되어 그 전기화학적 수소 발생 반응(Hydrogen Evolution Reaction, HER) 활성을 향상시켰다. 니켈 클로라이드가 도핑 소스로 사용되었으며, 에폭사이드 개시 졸-겔 방법을 통한 높은 용해도와 제어된 반응 속도 덕분에 RuOx 에어로겔 매트릭스에 균일한 도핑이 가능했다. 또한, RuOx 기반 에어로겔은 Ni 폼 표면에 성장하여 나노구조화 된 RuNi 합금 에어로겔이 되었다. 결과적으로, HER 활성의 향상이 달성되었다. 에폭사이드 개시 졸-겔 방법을 통해 원하는 구성의 금속 산화물의 화학양론을 제어할 수 있었다.

Electrochemically Active Melanin-like Polydopamine and Their Composites for Bioelectronic Applications

부스라 인하대학교 대학원 2025 국내박사

The field of bioelectronics, originating in the late 18th century with Luigi Galvani’s seminal experiments on electrical stimulation in animal tissues, has since grown into a transformative area of research and development. Fundamentally, bioelectronics aims to bridge the gap between biology and electronics, enabling interventions in cases of disorders or pathologies. For example, neural implants interpret brain signals, allowing individuals to control prosthetic limbs through thought alone, while portable glucose monitors enable diabetic patients to regulate their blood sugar levels more effectively. These applications highlight bioelectronics' positive impact on quality of life and its central role in advancing healthcare. This growing demand for bioelectronics in modern society makes it difficult to control the emergence of electronic waste, as majority of devices are based on metals and inorganic materials. To align with both "sustainability" and “seamless integration” with biological systems, future generations of electronics must prioritize designs that are low-cost, biodegradable, and recyclable, adhering to the principles of a circular economy. Simultaneously, these devices should be mechanically flexible, biocompatible, and both electronically and ionically conductive, ensuring a functional interface between biology and electronics. In this context, organic electronic materials, particularly conducting polymers, have emerged as promising alternatives due to their unique properties. However, the balance between biocompatibility and electrochemical performance remains a significant challenge for the broader application of conducting polymers. An alternative approach to address these limitations could involve partially or entirely substituting widely used synthetic conducting polymers like polyaniline, polypyrrole, and poly-3,4-ethylenedioxythiophene with naturally derived conjugated polymers, such as melanin, or their composites. Melanin, derived from the Greek word “melanos” meaning “dark,” was comprehensively defined as a pigment with diverse structures formed through the oxidation and polymerization of tyrosine in animals or phenolic compounds in other organisms. Melanin’s broad UV-visible absorption, metal-ion chelation, redox properties, hybrid ionic-electronic conductivity, biocompatibility and biodegradability suggest its suitability for bioelectronic applications. Melanin can be extracted from natural sources such as squid ink and black soldier fly, however, the final structure of melanin that is synthesized in vivo contains tightly bound biological components and metal cations within melanin. Any attempt to remove these proteins and other molecules may result in damaging the structural features and functionalities of melanin. Therefore, melanin-like polymers can be synthesized with enhanced structural control, circumventing the challenges posed by natural extraction methods. The most common procedure to obtain synthetic melanin is the auto-oxidation of dopamine (DA) precursors in aqueous buffers, resulting in the formation of polydopamine (PDA), also called as melanin- like polymer. The structure of melanin-like polymers, including their monomer composition, conjugation, and chain length, can vary depending on the preparation method, which consequently alters their properties. However, most studies focus on melanin’s roles as an adhesive, antioxidant, and biocompatible material rather than as a conductive component. This is predominantly due to the inherent insulating characteristics stemming from the conventional chemical synthesis of melanin. Only a few studies to date have achieved conductive melanin synthesis. This thesis explores the potential of melanin-like polymers for bioelectronics, highlighting their promising properties and potential advantages over conventional conducting polymers. To function effectively as active components in electronic devices, melanin-like polymers must possess conductive characteristics. Achieving this requires synthesizing a conjugated backbone structure under precisely controlled oxidative conditions. Therefore, we investigated the electrochemical synthesis of melanin-like polymers to ensure greater control over the final structure. Chapter 1 of this thesis provides an overview of bioelectronic design principles, focusing on natural and synthetic melanin-like polymers and their structure-property-function relationships. As the thesis aims to enhance the electrochemical properties of melanin-like polymers, background information on charge transport in organic materials and the electrical property of melanin is also provided. Chapter 2 discusses the electrochemical synthesis of highly conductive melanin-like polymers achieved through dopant engineering. To the best of our knowledge, this is the first study to systematically investigate the role of various counterions that can be incorporated into PDA during its electrochemical synthesis. Several counterions, including lithium perchlorate (LiClO4), hexafluorophosphate (KPF6), sodium p-toluene sulfonate (Na+-pTS), iron p-toluene sulfonate (Fe3+-pTS), and poly(sodium 4-styrenesulfonate) (PSS), were tested to determine their potential for electrochemically doping PDA to achieve conductivity. In Chapter 3, we further explore the incorporation of negatively charged, chemically synthesized poly(L-DOPA) nanoparticles as counterions during the electrochemical polymerization of PDA, creating melanin-like composites. After achieving high conductivity, we demonstrated the electrocatalytic activity of the resulting composite toward glucose oxidation. This material showed excellent performance in non-enzymatic glucose sensing, effectively addressing the stability issues common in enzyme-based glucose sensors, as well as the low selectivity and potential toxicity of metal nanoparticle-based non- enzymatic sensors. Chapter 4 investigates the integration of carbon-based materials, specifically liquid crystalline graphene oxide (LCGO), with PDA. The resulting PDA:LCGO composite exhibited enhanced electrochemical performance due to the synergistic effect of PDA’s conductivity and LCGO’s high surface area. Chapter 5 serves as a concluding chapter wherein we summarize the findings outlined in this thesis and propose future investigations that our work has made feasible. Overall, the multifunctional properties of melanin-like polymers, coupled with their biodegradability, offer a promising pathway for advancements in future bioelectronics, supporting new directions for developing medical diagnostics and therapy, with an environmentally responsible approach.