학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2018. 8. 박종래.The purpose of this study is to fabricate ultrahigh-strength carbon nanotube yarns
(CNTYs) for which the mechanical properties exced those of conventional high- performance fibers through theoretical and empirical aproaches for manufacturing
high-strength CNTYs. Due to the inherently superb mechanical properties and high
aspect ratios of CNTs, eforts to produce ultrahigh-strength CNTYs which properties
that exced those of conventional high-strength fibers such as carbon fibers have
continued over the last few decades. As a result, a variety of CNTY fabrication methods
have ben developed since the early 200s up to the present, and it is now posible to
produce continuous CNTYs with these methods. Nevertheles, macroscale CNTYs stil
fail to exhibit he excelent mechanical performance of nanoscale individual CNTs. To overcome these limitations, various atempts to improve the mechanical strength of
CNTYs have recently ben proposed. The mechanical and electrical properties of CNTs
difer depending on certain aspects of the nanostructure, such as the length, number of
wals, and the diameter of the nanotubes. In aditon, the microstructure of the CNT
asembly is closely related to the mechanical and electrical properties of the asembly.
Therefore, the most important isue is to control the nanostructure of CNTs and the
microstructure of the CNT asembly in order to fabricate ultrahigh-strength CNTYs.
Chapter 1 briefly describes the CNTYs and related factors that afect he mechanical
properties of yarns. The purpose of this study is to review recent studies on improving
these mechanical properties and to uncover isues and solutions that are thus far
unresolved.
Chapter 2 introduces and presents the atempts made to derive the theoretical
corelation betwen the structure and the CNTY strength based on the failure mechanism
of CNTYs. First, the relationship betwen the structural parameters of the nanostructures
of individual CNTs, the basic constiuents of yarns, and the mechanical strength of the
CNTYs is investigated. The efect of the microstructure of the CNT asembly on the
strength of CNTYs is then theoreticaly considered.
Chapters 3 and 4 discus the influence of the structural factors of CNTs as derived
from chapter 2 on the yarn strength. The efect of the nanostructure of the carbon
nanotubes on the mechanical properties of CNTYs is investigated by undertaking the
synthesis CNTYs made of CNTs with various nanostructures, after which the efects of
polymer chains on the internal structures of CNTYs and the yarn deformation behaviors
are studied.
Finaly, chapter 5 discuses developments related to ultrahigh-strength CNTYs
through croslinking considering the nanostructures and microstructures of CNTs based
on the theoretical and empirical understanding presented in the previous chapter.Chapter 1 Introduction 1
1.1 Overview of carbon nanotube yarns (CNTYs). 1
1.2 Theoretical consideration of the tensile strength of CNTYs 2
1.3 The state-of-the-art tensile performance of CNTYs. 5
1.3.1 Effect of different yarn formation processes on tensile performance of CNTYs 5
1.3.2 Effect of elementary CNT structure on CNTY strength . 9
1.3.2.1 Length of CNTs . 9
1.3.2.2 Diameter and number of walls of CNTs 11
1.3.2.3 Alignment of CNTs 14
1.3.2.4 Twist angle of CNTs. 17
1.3.3 Routes to improving the tensile strength of CNTYs 21
1.3.3.1 Physical densification 21
1.3.3.2 Polymeric or carbon mediator 26
1.3.3.3 Surface modification of CNTs. 28
1.3.3.4 Crosslinking between CNTs 34
1.4 Aim and scope of this study. 39
1.5 References 41
Chapter 2 Theoretical Approach to High-Specific Strength CNTYs 49 2.0 Major symbols. 49
2.1 Introduction. 50
2.2 CNTY model 51
2.3 Effect of the nanostructure on the CNTY strength 59
2.4 Effect of the bundle size on the CNTY strength. 67
2.5 Conclusion . 68
2.6 References 69
Chapter 3 Empirical Approach 1: Effects of the Nanostructure Characteristics of Individual Component CNTs on the CNTY Strength 72
3.1 Introduction. 72
3.2 Experimental . 74
3.3 Results and discussion. 77
3.4 Conclusion . 88
3.5 References 89
Chapter 4 Empirical Approach 2: Effect of the Bundling Behavior of Individual Component CNTs on the CNTY Strength 93
4.1 Introduction. 93
4.2 Experimental . 96
4.3 Results and discussion. 99
4.4 Conclusion . 125
4.5 References 126
Chapter 5 Empirical Approach 3: Strength Improvement by Controlling the Bundling Behavior and Chemical Crosslinking 132
5.1 Introduction. 132
5.2 Experimental . 135
5.3 Results and discussion. 137
5.4 Conclusion . 157
5.5 References 158
Abstract in Korean 162Docto
