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Hydrogels modified by amphiphilic structures
Heger, Richard ; Sedlařík, Vladimír (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
The submitted dissertation deals with the influence of amphiphilic structures on hydrogel properties. Additions of various amphiphilic substances associated with the formation of highly ordered structures affect the mechanical, transport and structural properties of hydrogels. The main inspiration for this type of work was living tissue, more precisely the extracellular matrix, which is often mimicked by hydrocolloids, and its high orderliness is responsible for its unique properties. The knowledge obtained from this tissue was applied to the hydrogel systems studied in this work. Various cross-linked hydrogel matrices (physically cross-linked agarose and gelatin, ionically cross-linked alginate and chemically cross-linked mixture of polyvinyl alcohol and chitosan) were suitable representatives for this work. These hydrogel systems were modified by the addition of various amphiphilic substances. The human body’s own phospholipid, lecithin, or variously charged more classic surfactants (CTAB, SDS and Triton X-100). Experimentally, this work is divided into three areas, the study of mechanical properties using rheology, the description of transport properties via release and flow experiments using various model drugs (rhodamine 6G, eosin B, amido black 10B, methylene blue and riboflavin), and morphological characterization using SEM. The characterization of hydrogel systems was supported by other techniques used in this work, such as drying and swelling experiments or gas sorption.
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Preparation, characterization of trimethylchitosan and verification of its interaction ability with regards to variable charged ionic compounds
Bayerová, Zuzana ; Pekař, Miloslav (referee) ; Smilek, Jiří (advisor)
The aim of this thesis is to study the interactions of trimethylchitosan with oppositely charged substances with regard to its potential biomedical use. A substantial step before the study of interactions was a successful synthesis of trimethylchitosan, which was subsequently confirmed by characterization of the final synthesis product using physico-chemical methods (infrared spectroscopy, elemental analysis, nuclear magnetic resonance). The result product was subjected to negatively charged interactions such as sodium dodecyl sulphate as a representative of the ionic surfactant, alginate as a natural polysaccharide representative and Chicago Blue as a representative of the anionic dye. The ability to interact with sodium dodecyl sulfate and alginate was demonstrated by the formation of hydrogels, which were subsequently characterized by mechanical viscosity tests using rheometric properties. The positive affinity of trimethylchitosan for organic dyes has been investigated in agarose-based support hydrogel matrices for changes in transport and barrier properties.
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Application of Graphene Membrane in Nanoelectronic Devices
Kormoš, Lukáš ; Drbohlavová, Jana (referee) ; Bartošík, Miroslav (advisor)
This diploma thesis is focused on the applications and fabrication of graphene membrane from graphene prepared by the chemical vapor deposition. Theoretical part deals with transport properties of the graphene and multiple scattering processes limiting the charge carrier mobility in this material. Included is short review of graphene membrane applications. Experimental part provides fabrication process for achieving suspended graphene device by utilizing electron beam lithography, focused ion beam, chemical etching and patterning of graphene. Graphene membrane is characterized by transport properties measurement and compared to non-suspended graphene.
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Interaction of low-energy electrons with graphene field effect transistors
Vysocký, Filip ; Kunc, Jan (referee) ; Čechal, Jan (advisor)
This diploma thesis is focused on fabrication of graphene field-effect transistors, characterisation of their transport properties and investigation of low-energy electron beam influence on the devices' properties under UHV conditions. The theoretical part of this work describes graphene fabrication methods, options of graphene transfer onto the substrates for graphene field-effect transistor manufacture. Furthermore, model of graphene doping via electrostatic interaction or photon, resp. electron beam exposition is explained. The experimental part of this work consist of manufacture of the graphene field-effect transistor in order to examine the change of its transport properties induced by doping of the graphene via low-energy electron beam exposition.
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Measurement of graphene transport properties
Nečesal, Daniel ; Procházka, Pavel (referee) ; Kormoš, Lukáš (advisor)
In order to create electronic devices utilizing graphene, it is necessary to manu- facture large sheets of high quality graphene which can be achieved by chemical vapor deposition (CVD). Mobility plays an important role in determining quality of graphene sheet because it is inversely proportional to concentration of defects. In this work, CVD graphene samples were fabricated, and their transport properties were characterized by van der Pauw and Hall bar methods. Graphene was transferred to samples either by using Fe(NO3)3 solution or via electrolytic delamination process. Both methods yiel- ded highly p-doped graphene. The electrolytic delamination transfer process resulted in a higher mobility of the graphene sheet and the Dirac point was observed due to a significant doping decrease.
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Fabrication of Graphene and Study of its Physical Properties
Procházka, Pavel ; Rezek, Bohuslav (referee) ; Kalbáč,, Martin (referee) ; Dub, Petr (advisor)
This doctoral thesis is focused on the preparation of graphene layers by Chemical Vapor Deposition (CVD) and their utilization for fabrication and characterization of field effect transistors. The theoretical part of the thesis deals with different methods of graphene production and measurement of its transport properties. In the first part of the experimental section the growth of polycrystalline graphene and individual graphene crystals with sizes up to 300 m is investigated. Further, graphene layer was also grown on an atomically flat copper foils, which were fabricated in order to achieve the growth of graphene of higher quality. Subsequently, the transport properties of field effect transistors produced from the grown layers were measured. The last two chapters deal with a doping of graphene layer by gallium atoms and X-ray radiation. Whereas the deposition of gallium atoms on the graphene surface causes chemical doping of graphene layer by charge transfer, X-ray irradiation of graphene field effect transistors induces the ionization of positively charged defects in dielectrics, which electrostatically dope a graphene layer.
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Transport properties of single graphene domains
Vysocký, Filip ; Kormoš, Lukáš (referee) ; Procházka, Pavel (advisor)
This bachelor thesis is focused on the preparation of single graphene domains by chemical vapor deposition method, its transfer onto non-conductive substrates and subsequent fabrication of the grapehene field effect transistors. The theoretical part of the tesis deals predominantly with different procedures of graphene production. The practical part of the thesis describes the production of graphene field effect transistors by electron beam lithography and the measurement of their transport properties.
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The hydrogen modification of the graphene structures for field effect transistors
Kurfürstová, Markéta ; Čermák,, Jan (referee) ; Mach, Jindřich (advisor)
This master’s thesis is focused on the subject of graphene modified with atomic hydrogen and its electronic transport properties. Structural and electronic properties of graphene and hydrogenated graphene are compared in the theoretical part of the thesis. The Raman spectroscopy technique is described, including characterization of typical Raman spectra of both unmodified and modified graphene. Samples used during experimental part of the thesis are prepared via laser and electron lithography, and are set to be measured in a vacuum chamber. Subsequently, electronic transport properties are measured before and after hydrogen modification of graphene. Finally, hydrogenated graphene is irradiated using electron beam and changes in its structure are analyzed with Raman spectroscopy techniques.
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Preparation and characterization of hydrogels with diffusion gradient
Tvrdoňová, Anna ; Pekař, Miloslav (referee) ; Smilek, Jiří (advisor)
The presented bachelor thesis deals with the preparation and further characterization of hydrogels with a diffusion gradient. The aim of the thesis is a literature research on the issue of hydrogels with a diffusion gradient, and a selection of a suitable method for its preparation. Moreover, conducted pilot experiments lead to the characterization of the properties of the prepared systems, especially with regard to proving the gradient structure of hydrogels. The performed evaluation was based on visual observation, determination of transport, and viscoelastic properties. In addition, a simple method consisting of weighing the prepared hydrogels was used. Hydrogels were compared depending on the choice of crosslinking agent, its concentration, and crosslinking time. Gradient hydrogels based on polysaccharide sodium alginate were prepared. The results suggest that by selecting the concentration of the crosslinking agent, as well as the crosslinking time, the final properties (viscoelastic and transport) of the hydrogels can be adjusted to the desired values. In the discussion of the results, we propose steps for a more comprehensive view of the issue and providing options for the following research.
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Corelation of transport and viscoelastic properties of hydrogels with diffusion gradient
Ščotková, Romana ; Sedláček, Petr (referee) ; Smilek, Jiří (advisor)
The aim of the presented bachelor thesis was to prepare hydrogels with diffusion gradient and to demonstrate the gradient structure of hydrogels in terms of viscoelastic and transport properties. With regard to potential biomedical applications, the cationic polysaccharide chitosan was selected for the preparation, especially for its antimicrobial and biocompatible properties. The resulting gradient hydrogels were subsequently characterized by oscillation tests to observe the differences using different concentrations and molecular weights of chitosan, crosslinking agent concentrations, dispersion environments for chitosan dissolution, and different gel crosslinking times. The samples were also subjected to drying experiments to confirm the gradient structure formed. The ability of the hydrogels to transport the active species was confirmed by visually evaluating the permeation of the anionic dye (bromothymol blue) during the gelation process. From the results obtained during the experimental part of the bachelor thesis it can be concluded that the viscoelastic properties of hydrogels can be modified by changing selected parameters during the preparation itself. It was also confirmed the assumption that with better mechanical properties of hydrogels there is a deterioration of transport properties. By controlled diffusion method, it was possible to prepare a hydrogel with a gradual gradient of crosslinking density, thus modifying the viscoelastic and transport properties.
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