Fabrication process and shielding characterization of graphene/metal/polymer nanocomposites for EMI shielding application전자파 차폐용 그래핀/금속/고분자 나노복합재료의 제조공정 및 차폐특성

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Graphene has been considered one of promising alternatives to EMI shielding material. The graphene, which features its outstanding electrical conductivity and large surface area, has advantages of density and corrosion resistance compared to conventional shielding materials. In order to accommodate graphene to practical use, as EMI shielding material, the agglomeration of graphene nanoplatelets must be overcome and the impedance of graphene has to be matched with that of free space. By using the molecular-level mixing process, graphene nanoplatelets decorated by magnetic nanoparticles are fabricated. In this research, RGO/Ni and RGO/Co nanocomposite powders are fabricated by a molecular-level mixing process by growing Ni nanoparticles on graphene surface for EMI shielding applications. Nanoparticles of uniform size are well distributed by interfacial bonding with functional groups on GO. Also, Graphene nanoplatelets (GNP) / Metal were fabricated with the same process to fabricate RGO/metal. GNP/Ni/Wax nanocomposites, fabricated by the molecular-level mixing process, showed SE value of 40dB in 8-12GHz. This is attributed to good electrical properties of GNP and functional groups that played an important role in the improvement of homogeneity of equal-sized nanoparticles and formation of efficient network improving the conductivity of composites. GNP/Ni/PMMA nanocomposites are fabricated by the solution blending process. Also, multi-layered functionally graded composition of GNP/Ni/PMMA nanocomposites are fabricated by the process in which mixed and degassed each layers of GNP/Ni/PMMA are packed layer by layer in a mold and pressed isostatically under a pressure. Analysis of EMI shielding mechanisms for multi-layered GNP/PMMA is carried out confirming calculation and experiment results of SER, SEA and SE have an aligned tendency with each other. Based on this analysis, multi-layered structure of GNP/Ni/PMMA nanocomposites are fabricated to maximize EMI shielding properties of GNP/Ni composites in the polymer matrix. In case of the multi-layered system with an alternating stack of dielectric polymer and conductive GNP fillers, the major shielding mechanism results from uneven distribution which increases the number of reflections between internal interfaces in the material. Absorption includes this effect from the sum of all interfaces formed on the conducting and insulating layers. While, the major shielding mechanism of the system of the conductivity gradient with GNP concentration is the absorption by conductive dissipation, which shows enhanced EMI shielding effectiveness. The progressive increase in conductivity from the surface causes the absorption of most of the power by conductive dissipation. In addition, additional shielding capability results from increased absorption from additional reflection with concentration gradient in the material. In particular, the multi-layered system ({15 wt% Ni/PMMA}/{20 wt% GNP/Ni/PMMA}/{30 wt% GNP/Ni/PMMA}/{40 wt% GNP/Ni/PMMA}) shows shielding effectiveness of 64 dB. These results suggest that GNP/Ni composites are highly promising EMI shielding material with the simple molecular-level mixing process at a low cost.
Advisors
Hong, Soon Hyungresearcher홍순형researcher
Description
한국과학기술원 :신소재공학과,
Publisher
한국과학기술원
Issue Date
2016
Identifier
325007
Language
eng
Description

학위논문(석사) - 한국과학기술원 : 신소재공학과, 2016.8 ,[xi, 90 p. :]

Keywords

EMI shielding; Graphene nanoplatetlets; Graphene/metal/polymer nanocomposites; multi-layered system; nanocomposites; 전자파 차폐; 그래핀 나노플레이트; 그래핀/금속/고분자 나노복합소재; 다층구조 시스템; 나노복합소재

URI
http://hdl.handle.net/10203/221612
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=663403&flag=dissertation
Appears in Collection
MS-Theses_Master(석사논문)
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