PhD Thesis Defence Presentations - George Paterakis
Abstract (Περίληψη)
In the framework of this PhD thesis, graphene from two different synthesis methods was used: (a) chemical vapor deposition (CVD graphene) and (b) graphite peeling (GO). Each of them has different properties and is suitable for different applications. Apart from that, however, both types of graphene were further modified to change their properties and study them through different applications. In the case of CVD graphene, transparent heating devices are developed, through which is studied the effect of doping on the electrical, thermal, and optical properties of graphene. At the same time, in the case of GO, graphene-type anti-corrosion coatings are developed on metal substrates, through which is studied the effect of the structural modifications of GO on its barrier properties and chemical stability.
The basic concepts related to graphene (Chapter 1), heating devices (Chapter 2) and corrosion of metals (Chapter 3) are analyzed in the theoretical part, while Chapter 4 mentions the experimental methodology followed for carrying out the measurements. Then, in the first part of the results (Part I), the properties of the graphene materials are studied after their synthesis as well as after the respective modifications (Chapters 5 and 6), while in the second part (Part II) their properties are studied through the functional characteristics of the respective experimental devices (Chapters 7 and 8). The last chapter (Chapter 9) summarizes all the conclusions that emerged from the study of graphene materials and their properties.
In the case of CVD graphene, the structural and spectroscopic characteristics are first examined in both growth and transfer stages. This optimization allows the reduction of the imperfections of its lattice, which are responsible for the limitation of its properties. In addition, the interfacial connection of graphene with the polymer transfer layer is examined in detail, both macroscopically and at the nanoscale. While at the same time, the adhesion energy is studied as a function of temperature up to 200 ° C. The interfacial study contributes to the stability of the graphene structure and the further reduction of its lattice defects. Moreover, the enhancement of the graphene's properties is studied through its doping by aqueous solutions of the metal chlorides of FeCl3, CuCl2 and AuCl3. The results of the study show the interaction of graphene with the different doping molecules formed on the lattice, as well as the significant change in its electrical and optical properties.
Further investigation of the properties of CVD graphene is done through transparent heating devices, which are developed in various series of transparent heating devices are developed, in terms of dimensions, the number of graphene sheets, and the doping method on them. The electrothermal characterizations of the devices show the changes caused by doping on both the electrical and thermal properties of graphene. In addition, corresponding results are obtained also from the macroscopic analysis of the performance characteristics of the devices, regarding the stability of their operation as a function of time and the distribution of temperature in their structure, which is a consequence of the properties of graphene.
In the case of GO, a new method of chemical synthesis is being developed, with the aim of optimizing its properties for the development of anti-corrosion coatings. During the synthesis, the modifications of its properties are directly related to the modification of its structure in terms of the lateral size, the exfoliation degree and the presence of oxygen groups in its lattice.
The investigation of anti-corrosion properties of GOs is considered through their anti-corrosion coatings on the surface of metal substrates. The anti-corrosion coatings developed to differ both in thickness from a few nm to ~ 1 μm, and the material, coatings consisting exclusively of GOs or nanocomposite coatings of them. While at the GOs coatings are considered to further improve their properties through their reduction after coating. In the case of thin coatings is considered the protective effect that GOs can provide against corrosion of aluminum foil, where the reduced forms of GO show high levels of aluminum protection in 0.5 M H2SO4 and 1M LiClO4, and much higher compared to commercially available specimens. At the same time, in 1 μm thick coatings, are studied the anti-corrosion efficiency of different reduced forms of GO in the protection against corrosion of aluminum, copper and iron, in environments of H2SO4 0.5 M and NaCl 3.5 %. From the comparison of the results of the above coatings is evaluated the possibility of modification of the GO after its coating. Finally, the protective efficiency of thermally expanded and reduced GO nanocomposites is examined against the corrosion of copper in H2SO4 0.5 M, which results in a significant increase in the degree of protection of epoxy resin with the addition of just 0.1% graphene material.
Speakers Short CV (Σύντομο Βιογραφικό Ομιλητή)
George Paterakis received his university degree in the Department of Materials Science (Univ. of Patras) in 2012. In 2015 he obtained his MSc degree from the Interdepartmental Program of Polymer Science and Technologies of the University of Patras. His Master's thesis entitled “Photovoltaic devices with the use of conjugated polymers and graphene sheets” was held at the Laboratory of Composite and Nanocomposite Materials of ICEHT/FORTH, under the supervision of Professor C. Galiotis. He then joined the Doctoral Studies Program of the Department of Chemical Engineering of the University of Patras to conduct his PhD Thesis, in which he was involved in the synthesis of graphene materials, the modification of their properties and the development of innovative applications. The scientific results that have emerged during his postgraduate studies have led to the publication of fifteen peer-reviewed articles in several international scientific journals. He has received the ELIDEK scholarship for doctoral candidates and has participated in several national and international research programs.