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Title:Thermal, electrical and mechanical properties of three-dimensional functional materials
Author(s):Kang, Jin Gu
Director of Research:Braun, Paul V.
Doctoral Committee Chair(s):Braun, Paul V.
Doctoral Committee Member(s):Cahill, David G.; Sinha, Sanjiv; Shoemaker, Daniel P.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Colloidal assembly, 3D functional materials
Abstract:Colloidal assembly is a dynamic phenomenon where the particulates dispersed in fluids, with the size over tens of nms to several μms, form into specific spatial organization resulting from the variations in the surroundings. The general hard sphere colloids with charged surfaces can be self-assembled into the periodic arrays during the drying process of the fluids. These static periodic arrays, namely, colloidal crystals do not possess any dynamic functionalities, but serve as a sacrificial template for the fabrication of various classes of 3D functional materials. On the other hand, some colloids themselves have their own dynamic functionalities, so that they can be directed-assembled in response to external triggering forces. These particles serve as an active element that offers dynamic changes in the properties of the material systems. The inorganic 3D functional meso/nanostructures were developed for the potential uses in thermal management applications using the self-assembled colloidal crystals as the template. Especially, the Fe3O4 was epitaxially grown through the complex 3D colloidal templates, after which the single crystal Fe3O4 3D porous structures were obtained. These materials have the multiple nanosized 3D interfaces to deter the phonon transport, and at the same time consist of the single crystals to enhance the electron transport. Through various kinds of analysis tools, we thoroughly characterized the materials, particularly focusing on the crystallinity, the density, the thermal conductivity, and the electrical conductivity. The epitaxial Fe3O4 nanoporous structures including the pores with 40 nm in diameter were identified to be thermally insulating and electrically conductive at the same time. The dynamically reconfigurable colloidal assembly in the viscoelastic fluids was investigated with the ultimate goals of the energy harvesting. As the first step, two different methods of integrating the colloids into the viscoelastic media were developed. The PNIPAM colloids, which intrinsically possess the thermo-responsive functionality, were synthesized by two kinds of polymerization routes, and then incorporated into the fibrin networks hydrogels using the method developed. The PNIPAM microgels/fibrin networks hydrogel composites demonstrated the reversibly switchable mechanical property, which is multifold jump in the storage modulus due to the strain-stiffening of fibrin networks, in response to the external temperature changes.
Issue Date:2018-12-02
Rights Information:Copyright 2018 Jin Gu Kang
Date Available in IDEALS:2019-02-08
Date Deposited:2018-12

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