Thermal response and applications of graphene-based macrostructures and their composites
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Authors
Li, Mingxin
Issue Date
2023-12
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Mechanical engineering
Alternative Title
Abstract
Single-layer graphene displays many unique attributes, including record-breaking thermal conductivity, charge carrier mobility, fracture strength, and Young’s modulus, and thus possesses immense potential for a wide range of technological applications in electronics, photonics, nanocomposites, etc. However, it has been challenging to translate the outstanding mechanical, electrical, and thermal properties of single-layer graphene into that of macroscale graphene assemblies, significantly constraining their applicational potentials. In this thesis, several approaches have been developed to fabricate wet-spun graphene macrostructures and their composites, including graphene fibers, hollow graphene tubes, their 3D assemblies, and composites. The graphene macroscopic structures and assemblies display excellent thermomechanical and electrical properties resulting from the inherent properties of single-layer graphene, optimization of their microstructures, and designed material interactions.In particular, to fabricate a high-performance graphene macroscopic structure with both ultrahigh electrical and thermal conductivity, a new electroplating process has been developed to deposit uniform micrometer-level thin copper coatings onto graphene fibers. The electroplating process has also been applied to wet-fused graphene fiber fabrics. The resulting copper-coated graphene fiber fabrics not only gain the high electrical conductivity of copper but also have high flexibility and retain the high thermal conductivity of graphene fibers owing to the conductive junctions between wet-fused graphene fibers.
Building upon the knowledge of fabricating highly thermally conductive graphene fibers, a fast-coagulating coaxial wet-spinning method has been developed to fabricate hollow graphene tubes (HGTs) with high thermal conductivity. By filling the bore of the graphene tubes with 1-octadecanol, a graphene-based phase change composite has been developed, exhibiting extraordinarily high latent heat exceeding that of pure 1-octadecanol. The counterintuitive finding is explained through experimental and literature studies of the interactions between graphene and 1-octadecanol, which results in lattice contraction of the latter, resulting in an abnormally higher phase change enthalpy. This finding contrasts with the conventional wisdom that adding a non-phase changing filler such as graphene into the phase change composite will reduce the latent heat and, thus, heat storage capacity.
A moisture-fusing method of HGTs has been developed based on the wet-fusing of graphene fibers. Without changing the tubular morphology of the HGTs, individual tubes have been layer-by-layer moisture-fused to form an interconnect graphene tube macrostructure with high thermal conductivity. These graphene tube macrostructures have been filled with 1-octadecanol dispersed with multiwalled carbon nanotubes. The resulting phase change composite exhibits high visible light absorption, fast thermal response, and a high heat storage capacity. These traits ensure high solar-thermal conversion and storage efficiency of the composite at low carbon weight percentages, making them suitable for large-scale solar-thermal energy harvesting applications.
In addition, a thermally conductive yet mechanically stretchable composite graphene fiber has also been developed by wet spinning a mixture of graphene oxide, bacterial cellulose, and EGaIn liquid metal. A stretchable link is formed between graphene oxide sheets within the composite fiber by grafting thin bacterial cellulose polymers between them. The grafted bacterial cellulose fibrils keep the composite fiber mechanically intact at large tensile strains. The good thermal conductivity of the composite fiber is ensured by its well-aligned graphene sheets. EGaIn provides an electrical percolation path within the composite fiber, allowing for high electrical conductivity. Adding EGaIn also helps reduce Young’s modulus of the composite fiber. At the end of this work, further experiments are proposed to validate the applicational potentials of the stretchable and electrically and thermally conductive composite graphene fibers.
Description
December 2023
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY