|
|
Electrospinning of polyvinylidenfluoride based fibers
Hošek, František ; Šťastný, Přemysl (referee) ; Částková, Klára (advisor)
Electrospinning is one of the rapidly developing methods for obtaining fibers of very small thickness. There is a wide-scale use of nanofibers, and it has a great potential in many fields, such as in medicine, biology, chemistry, electronics, environmental protection, energy-harvesting, and other. Polyvinylidene fluoride (PVDF) appears to be a promising material for fiber production for its excellent mechanical and chemical properties. It is a chemically inert substance, very resistant to thermal stress. The aim of this bachelor thesis is the preparation of PVDF fibers by electrospinning and the study of the influence of three different surfactants on the spinnability of PVDF, on the arrangement and the shape of fibers which are formed during electrospinning. The effect of surfactant concentration (1 wt%; 0.5 wt%; 0.25 wt%) on the spinning process at electrical voltages of 25 kV and 50 kV was studied. The theoretical part describes the properties and the division of polymers and looks at polyvinylidene fluoride (PVDF) as a source material in more detail. Furthermore, the electrospinning method is described, including process conditions and external parameters influencing the process of obtaining fibers. The experimental part describes the preparation of samples by electrospinning and their characterization. Fiber thickness, its appearance, arrangement, and the occurrence of defects when using individual surfactants were evaluated. It was found that the used ionic surfactants affect the thickness of the fibers and their morphology. Homogeneous fibers with a predominant arrangement in one direction, without defects, were obtained.
|
|
|
Energy dispersive X-ray spectroscopy of doped PVDF fibers
Smejkalová, Tereza ; Papež, Nikola (referee) ; Sobola, Dinara (advisor)
Tato diplomová práce zkoumá flexibilní materiál k produkci elektřiny založený na piezoelektrickém polymeru Polyvinylidenfluorid (PVDF). Inkorporací piezoaktivní keramiky lze vlastnosti piezoelektrického polymeru PVDF významně zlepšit a převést na užitečnou elektrickou energii. PVDF byl vytvořen elektrostatickým zvlákňováním do vláken o tloušťce 1,5-0,3 µm a poté studován různými analytickými metodami. Tato práce nabízí popis elektrostatického zvlákňování, přípravu vzorků a teoretický úvod do analytických metod, kterým byly vzorky podrobeny. Morfologie a distribuce nanostrukturované keramiky do polymerní matrice PVDF byla pozorována použitím skenovací elektronové mikroskopie (SEM) a energiově disperzní spektroskopie (EDX). Pro tvorbu fáze a podrobné fázové složení byly vzorky charakterizovány infračervenou spektroskopií s Fourierovou transformací (FTIR). Práce také obsahuje analýzu s použitím Ramanovy spektroskopie, metody používané k identifikaci a porovnání chemických sloučenin. Elektrické vlastnosti byly studovány dielektrickou spektroskopií a je poskytnuta korelace se složením. Jednotlivé komponenty dotovaných vláken jsou charakterizovány a vyhodnocovány v souvislosti s jejich budoucím využitím v senzorech.
|
|
|
Investigation of high voltage influence on different materials in high and low vacuum
Šedivý, Matúš ; Šandera, Josef (referee) ; Hejátková, Edita (advisor)
The beginning of this thesis contains an overview of properties of the insulators, and description of insulators that were used for in depth research of surface breakdown in vacuum. Furthermore, this work focuses on mechanisms of an electric breakdown initiation at the interface of the solid insulator and surrounding low pressure gas. Multiple methods for measurements of dielectric strength are examined. The experimental part describes the measurements performed in the vacuum chamber. The results of these measurements are then analysed. In conclusion, used insulators are compared and suggestions for further work are given.
|
|
|
Electrospinning of composite fiberous structures for piezoapplications
Schifferová, Zuzana ; Kaštyl, Jaroslav (referee) ; Částková, Klára (advisor)
Polymer and composite polymer-ceramic nanofibers were prepared by electrospinning process. Solution of 20 wt.% polyvinylidene fluoride (PVDF) in a mixture of dimethyl sulfoxide (DMSO) and acetone in the ratio of 7:3 was chosen as the most suitable precursor. When preparing composite nanofibers, 20 wt.% of barium calcium zirconate titanate (BCZT) or barium titanate (BT) nanoparticles was added to this PVDF solution. Given parameters were defined as the most suitable for the process of electrospinning: voltage of 50 kV, feeding rate of 30 l/min, distance between emitter and collector of 20 cm and needle diameter of 17 G. The effect of polymer molecular weight and the rotation speed of collector was also studied. Various properties of prepared samples were studied: morphology and fiber diameter, phase composition with the use of x-ray diffraction and Fourier transform infrared spectroscopy and also chosen electrical properties. Lower fiber diameters appeared with lower polymer molecular weight and higher rotation speed of the collector. These parameters resulted in higher percentage of the piezoelectric phase as well. The smallest achieved fiber diameter was around 300 nm, the highest percentage of phase was 92 % and the highest piezoelectric constant had a value of 16 pC/N. Composite fibers filled with BT particles showed better properties that the ones filled with BCZT particles.
|
|
|
Electrode Materials for Li-S Batteries
Jaššo, Kamil ; Almáši,, Miroslav (referee) ; Syrový,, Tomáš (referee) ; Kazda, Tomáš (advisor)
This thesis is focused on the research of electrode materials for lithium-sulphur (Li-S) batteries, with an emphasis on the optimization of the process of preparation of positive electrodes through the modification of the individual technical steps of the manufacturing process and the selection of a suitable binder. The theoretical part of the thesis is devoted to terminology and battery issues with emphasis on Li-S batteries, their working principle, shortcomings, critical parameters for commercialization and existing research in this field. The practical part of the thesis deals with the influence of the compression pressure used in the production of positive electrodes on the electrochemical properties of the resulting Li-S cells. In the next part of the thesis, the influence of the binder used on the resulting electrochemical properties is investigated. In the following sections, the influence of the thickness of the electrode material layer and the ratio of its individual components (C/S) on the resulting electrochemical properties of the Li-S cell is analyzed. On the basis of the measured results, the optimum conditions for the preparation of the positive electrodes of the Li-S cells have been identified with respect to the individual technical steps of the manufacturing process.
|
|
|
Electrospinning of polyvinylidenfluoride based fibers
Hošek, František ; Šťastný, Přemysl (referee) ; Částková, Klára (advisor)
Electrospinning is one of the rapidly developing methods for obtaining fibers of very small thickness. There is a wide-scale use of nanofibers, and it has a great potential in many fields, such as in medicine, biology, chemistry, electronics, environmental protection, energy-harvesting, and other. Polyvinylidene fluoride (PVDF) appears to be a promising material for fiber production for its excellent mechanical and chemical properties. It is a chemically inert substance, very resistant to thermal stress. The aim of this bachelor thesis is the preparation of PVDF fibers by electrospinning and the study of the influence of three different surfactants on the spinnability of PVDF, on the arrangement and the shape of fibers which are formed during electrospinning. The effect of surfactant concentration (1 wt%; 0.5 wt%; 0.25 wt%) on the spinning process at electrical voltages of 25 kV and 50 kV was studied. The theoretical part describes the properties and the division of polymers and looks at polyvinylidene fluoride (PVDF) as a source material in more detail. Furthermore, the electrospinning method is described, including process conditions and external parameters influencing the process of obtaining fibers. The experimental part describes the preparation of samples by electrospinning and their characterization. Fiber thickness, its appearance, arrangement, and the occurrence of defects when using individual surfactants were evaluated. It was found that the used ionic surfactants affect the thickness of the fibers and their morphology. Homogeneous fibers with a predominant arrangement in one direction, without defects, were obtained.
|
|
|
Energy dispersive X-ray spectroscopy of doped PVDF fibers
Smejkalová, Tereza ; Papež, Nikola (referee) ; Sobola, Dinara (advisor)
Tato diplomová práce zkoumá flexibilní materiál k produkci elektřiny založený na piezoelektrickém polymeru Polyvinylidenfluorid (PVDF). Inkorporací piezoaktivní keramiky lze vlastnosti piezoelektrického polymeru PVDF významně zlepšit a převést na užitečnou elektrickou energii. PVDF byl vytvořen elektrostatickým zvlákňováním do vláken o tloušťce 1,5-0,3 µm a poté studován různými analytickými metodami. Tato práce nabízí popis elektrostatického zvlákňování, přípravu vzorků a teoretický úvod do analytických metod, kterým byly vzorky podrobeny. Morfologie a distribuce nanostrukturované keramiky do polymerní matrice PVDF byla pozorována použitím skenovací elektronové mikroskopie (SEM) a energiově disperzní spektroskopie (EDX). Pro tvorbu fáze a podrobné fázové složení byly vzorky charakterizovány infračervenou spektroskopií s Fourierovou transformací (FTIR). Práce také obsahuje analýzu s použitím Ramanovy spektroskopie, metody používané k identifikaci a porovnání chemických sloučenin. Elektrické vlastnosti byly studovány dielektrickou spektroskopií a je poskytnuta korelace se složením. Jednotlivé komponenty dotovaných vláken jsou charakterizovány a vyhodnocovány v souvislosti s jejich budoucím využitím v senzorech.
|
|
|
Electrospinning of composite fiberous structures for piezoapplications
Schifferová, Zuzana ; Kaštyl, Jaroslav (referee) ; Částková, Klára (advisor)
Polymer and composite polymer-ceramic nanofibers were prepared by electrospinning process. Solution of 20 wt.% polyvinylidene fluoride (PVDF) in a mixture of dimethyl sulfoxide (DMSO) and acetone in the ratio of 7:3 was chosen as the most suitable precursor. When preparing composite nanofibers, 20 wt.% of barium calcium zirconate titanate (BCZT) or barium titanate (BT) nanoparticles was added to this PVDF solution. Given parameters were defined as the most suitable for the process of electrospinning: voltage of 50 kV, feeding rate of 30 l/min, distance between emitter and collector of 20 cm and needle diameter of 17 G. The effect of polymer molecular weight and the rotation speed of collector was also studied. Various properties of prepared samples were studied: morphology and fiber diameter, phase composition with the use of x-ray diffraction and Fourier transform infrared spectroscopy and also chosen electrical properties. Lower fiber diameters appeared with lower polymer molecular weight and higher rotation speed of the collector. These parameters resulted in higher percentage of the piezoelectric phase as well. The smallest achieved fiber diameter was around 300 nm, the highest percentage of phase was 92 % and the highest piezoelectric constant had a value of 16 pC/N. Composite fibers filled with BT particles showed better properties that the ones filled with BCZT particles.
|
|
|
Investigation of high voltage influence on different materials in high and low vacuum
Šedivý, Matúš ; Šandera, Josef (referee) ; Hejátková, Edita (advisor)
The beginning of this thesis contains an overview of properties of the insulators, and description of insulators that were used for in depth research of surface breakdown in vacuum. Furthermore, this work focuses on mechanisms of an electric breakdown initiation at the interface of the solid insulator and surrounding low pressure gas. Multiple methods for measurements of dielectric strength are examined. The experimental part describes the measurements performed in the vacuum chamber. The results of these measurements are then analysed. In conclusion, used insulators are compared and suggestions for further work are given.
|
guest ::
