Title Page

Abstract

Contents

Chapter 1. Introduction 11

1.1. Study Background 11

1.2. Purpose of Research 13

Chapter 2. Fabrication 16

2.1. Overview 16

2.2. Fabrication Parameters 17

2.3. General Characterization 22

2.4. Method 28

Chapter 3. Mass transporation in AACNF 32

3.1. Overview 32

3.2. Viscous Flow 33

3.3. Microparticle 37

3.4. Method 41

Chapter 4. Applications 45

4.1. Hydrogel Integration 45

4.2. Microbial Fuel Cell 51

4.3. Method 59

Chapter 5. Conclusion and Perspectives 62

Bibliography 64

국문 초록 67

Figure 1. Examples of template electrodes with various size scale. (a) Carbon paper. (b) Carbon cloth. (c) Graphene-oxide foam. (d) Ni foam. (e)... 12

Figure 2. Visualization of Ag and Au distribution in AACNF using SEM and EDS elemental mapping. 13

Figure 3. The schematic illustration of the AACNF as template electrode for nanometer to micrometer scale substances. 14

Figure 4. Hierarchical structures of AACNF with the PAAm hydrogel (a), PEDOT:PSS hydrogel (b), the fibroblast cell (c), and the Geobacter Anodireducens (d). 15

Figure 5. The schematic illustration of the fabrication principle for AACNF. 16

Figure 6. The schematic illustration of the different states of PVP on the AgNW surface with respect to the existence of ethanol. 16

Figure 7. Photographic images comparing the morphology of AACNF fabricated without (a) or with (b) ethanol. 17

Figure 8. (a) The morphology of the fabricated AACNF with respect to the ethanol volume fraction. (b) The plot of fabricated AACNF volumes against the... 19

Figure 9. (a) The morphology of the fabricated AACNF with respect to the weight ratio of the Au against the Ag. (b) ICP-MS analysis of the released Ag ions from... 20

Figure 10. The morphology of the fabricated AACNF (a) and the plot of electrical conductivity (left axis) and density (right axis) of the AACNF (b) with respect to... 21

Figure 11. Comparing AACNF and previously reported studies on the relationship between electrical conductivity and density. 22

Figure 12. (a) Fabrication process of the sample for measuring the electrical conductivity of the AACNF over time. (b) Photographic images measuring the... 24

Figure 13. Normalized electrical conductivity of the AACNF with varying densities against the synthesis time. 24

Figure 14. (a) Photographic images of printed letter, "Ag Au" (i), and the printed letters seen through the 1 mm thick AACNF with 0.2 wt% of NWs (ii) and 0.5 wt%... 25

Figure 15. Transmittance spectra of the 1 mm thick AACNF with varying densities by UV-Vis spectroscopy. 26

Figure 16. (a) a photographic image of the UTM setup for compressive stress-strain curve measurements. The diameter of the UTM compression platen was 50... 27

Figure 17. (a) Examples of substances on the nanometer to micrometer scale that is permeable into AACNF. (b) The super-porous structure demonstrated by AACNF... 32

Figure 18. (a) AACNF samples to test the effect of the NW density. (b) The compression-mold for AACNF with NW densities from 1.0 to 4.0 wt%. 34

Figure 19. (a) Diagram of the experimental setup diagram to measure viscous permeability of porous materials via pressure difference and mass flux across the... 34

Figure 20. (a) Viscous permeability against volumetric flux across the AACNF with different weight percent of NWs from 0.25 to 2.0. The error bars are the s.d.... 35

Figure 21. (a) Diagram of the two-chamber diffusion cell to measure the mass diffusivity across the porous material. (b) Photograph of the mass diffusivity test.... 35

Figure 22. (a) The glucose concentration over time measured from the receptor chamber according to varying densities of AACNFs. The error bars are the s.d. for... 36

Figure 23. The schematic illustration of cell-embedding, incubation and observation process, with the L929 cells requiring 24-36 hours of settlement time.... 38

Figure 24. The microscopic image (bright-field/live/dead) of L929 cells settled on the 3D nanowire matrix of AACNF (0.25 wt% NWs) at 36 h the cell viability... 38

Figure 25. Seven days of viability test conducted on L929 cells showing the biocompatibility of AACNF. 39

Figure 26. Microscopic images (DAPI) of L929-embedded AACNFs of varying NW densities, showing cell distribution by depths from the top surface. The L929... 40

Figure 27. The cell population ratio by depth from the top of the AACNF with varying densities. The error bars are the s.d. for N＝4 samples. 40

Figure 28. The schematic comparison of the PAAm hydrogel-embedded AACNF fabrication process (a) and the PAAm hydrogel with AgNWs (b). 45

Figure 29. The fabrication process for PAAm hydrogel-embedded AACNF. 46

Figure 30. Electrical conductivity of the AACNF, PAAm hydrogel-embedded AACNF, and the PAAm hydrogel with AgNWs against the weight percent of the... 46

Figure 31. Photographic images of PAAm hydrogel-embedded AACNF with different NW content before and after stretching. 47

Figure 32. Cross-sectional SEM images of the stretched PAAm hydrogel-embedded AACNF with different densities. AACNF with 0.4wt% of NW under 0%... 48

Figure 33. (a) A photographic image of the PEDOT:PSS hydrogel-embedded AACNF before the cut. (b) A photographic image of the PEDOT:PSS hydrogel-... 48

Figure 34. (a) Fabrication process of the sample for measuring the electrical conductivity of the PAAm hydrogel-embedded AACNF before and after stretching.... 50

Figure 35. (a) Relative resistance with respect to the strain applied to the PAAm hydrogel-embedded AACNF with varying NW content. (b) Cyclic loading and... 50

Figure 36. (a) The schematic illustration of the operating mechanism of a single-chamber MFC using AACNF as an anode electrode. (b) Photographic image of the... 52

Figure 37. SEM images of the geobacter anodireducens culture inside the AACNF (a-c) and on the dense 2D network of NWs(d). 52

Figure 38. Polarization curve (a) and power density curve (b) of the MFC using AACNF as an anode with respect to the microbial culture time. 53

Figure 39. The analytic method of analyzing the polarization curve of a microbial fuel cell (MFC). 55

Figure 40. (a) Polarization curves of the MFC with varying densities of the AACNF. The error bars are the standard deviation (s.d.) for N＝5 samples. (b)... 57

Figure 41. MFC maximum power against time for 25 days of long-term operation. The red arrow indicates the basal broth supply to the Geobacter anodireducens... 58

 템플릿 전극은 에너지 소자, 생체전극 등 기능성 전극의 기본골격으로서 활용되어 최종적인 응용에서 전체적인 성능에 결정적인 영향력을 가질 수 있는 중요한 요소이다. 코어-쉘 나노와이어는 코어 및 쉘 물질의 상호보완적 효과로 인해 차세대 템플릿 전극의 기본 재료로서 높은 기대를 받고 있으나, 최종적인 전극의 형상적 한계나 제조 공정상의 확장성 제약 등의 문제로 인해 실용적인 응용에는 제한이 있는 상황이다. 본 연구에서는 나노 웰딩 합성 기법을 기반으로, 원스텝 공정을 사용하여 제작할 수 있는 고다공성 Ag-Au 코어-쉘 나노와이어 폼(AACNF)을 소개한다. AACNF는 금속 기반 전극 중에서도 가장 낮은 밀도를 가지면서도, 이례적으로 높은 전기전도도(99.33-753.04 S m-1)를 보여주었으며, 우수한 물질 전달 특성으로 인해 고분자 전구체와 생체세포와 같은 다양한 기능성 물질과 다중 규모의 계층 구조를 형성할 수 있음을 확인하였다. AACNF의 합성과정에서 동반되는 나노 웰딩 현상으로 인해 AACNF는 기계적 인장에 대해 높은 안정성을 가졌으며, 하이드로겔 등의 이차물질과 계층적인 방식으로 융합하였을 때 단순히 혼합한 형태와 비교하여 10,000배 이상 높은 전도도를 나타내었다. AACNF는 공극의 크기도 마이크로미터 수준이 되도록 조절이 가능하며, 섬유아세포와 외전기성 미생물 등 1-10 μm 규모의 큰 입자들도 내부로 침투하여 계층적인 융합이 가능하였다, 특히, AACNF 기반 미생물 연료전지는 최적의 밀도 범위 내에서 높은 출력밀도(~ 330.1 W m-3)를 기록하여 생체 전극 및 에너지 소자용 전극으로서의 가능성을 확인하였다. AACNF는 그 고유한 특성으로 인해 다양한 크기 규모의 물질들과 계층 구조를 형성하는 데 있어서 향후 진보된 에너지 장치 및 생체융합 전극 분야 템플릿 전극으로서 폭넓게 활용될 수 있을 것으로 기대된다.