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Effect of sub-micrometer structural features on rheology of polymer nanocomposites
Lepcio, Petr ; Chodák,, Ivan (referee) ; doc.Ing.Marián Lehocký, Ph.D. (referee) ; Jančář, Josef (advisor)
Polymerní nanokompozity (PNCs) mají slibnou budoucnost jako lehké funkční materiály zpracovatelné aditivními výrobními technologiemi. Jejich rychlému rozšíření však brání silná závislost jejich užitných vlastností na prostorovém uspořádání nanočástic (NP). Schopnost řídit disperzi nanočástic je tak klíčovým předpokladem pro jejich uplatnění ve funkčních kompozitech. Tato práce zkoumá přípravu polymerních nanokompozitů v modelové sklotvorné polymerní matrici roztokovou metodou, technikou schopnou vytvářet prostorové uspořádání nanočástic řízené strukturními a kinetickými parametry přípravného procesu. Prezentované výsledky popisují rozdíly mezi změnami rheologického chování roztoku polystyrenu při oscilačním smyku s vysokou amplitudou (LAOS) vyvolanými nanočásticemi. Výsledky vedou k závěru, že vysoce-afinní OP-POSS nanočástice při nízkých koncentracích dobře interagují s PS a tvoří tuhé agregáty, zatímco nízko-afinní OM-POSS nanočástice za těchto podmínek neovlivňují deformační chování polymerních řetězců. Dále byla pozornost zaměřena na vliv použitého rozpouštědla na uspořádání nanočástic v SiO2/PMMA a SiO2/PS nanokompozitech, který je v literatuře prezentován jako parametr řídící prostorové uspořádání nanočástic v pevném stavu. Důraz byl kladen na kvalitativní rozdíly mezi „špatně dispergovanými“ shluky nanočástic, které byly na základě rheologie a strukturální analýzy (TEM, USAXS) identifikovány jako polymerními řetězci vázané nanočásticové klastry a dva typy agregátů, jeden termodynamického a druhý kinetického původu. Jednotlivé druhy agregátů se vyznačují odlišnými kinetikami vzniku a rozdílnými vlastnostmi jak mezi sebou, tak v porovnání s dispergovanými nanočásticemi. Pozorované typy disperze nanočástic byly kvantitativně posouzeny podle svých rheologických vlastností během roztokové přípravy, podle kterých byla vyhodnocena míra adsorpce polymeru na povrch nanočástic a atrakce ve vypuzeném objemu. Výsledky byly porovnány s teorií PRISM. Důležitost uspořádání nanočástic byla demonstrována na porovnání teplot skelných přechodů různých struktur při stejném chemickém složení.
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Manufacturing of calcium phosphates and silica based scaffolds for bioapllications
Virágová, Eliška ; Hadraba, Hynek (referee) ; Částková, Klára (advisor)
The aim of this diploma thesis was to prepare porous bioceramic scaffolds based on calcium phosphates and calcium phosphates doped with silica. Scaffolds are intended to be used in bone tissue engineering. Two main preparation methods were used for the creation of scaffolds – replica method and direct foaming method. Theoretical part of the diploma thesis is focused on a general description of the skeletal system, biomaterials and methods of preparation of highly porous calcium phosphate ceramics. Experimental part contains a description and the results of prepared scaffolds by above mentioned methods. The preparation process by the direct foaming method was optimized to obtain a defined structure. Calcium phosphate scaffolds containing 0–20 wt.% SiO2 were sintered and studied in terms of material characteristics (phase composition, pore size and porosity, microstructural study by scanning electron microscopy (SEM)), bioactive properties (simulated body fluid (SBF) interaction tests and tests of simulated degradation) and mechanical properties in order to evaluate the effect of silica doping. Scaffolds prepared by both methods were composed of a mixture of hydroxyapatite and/or tricalcium phosphate and cristobalite and wollastonite with comparable porosity in the range of 80–88 %. The pore size of the scaffolds prepared by the direct foaming method reached the interval of 5–250 µm opposite to template method reached the pore size up to 430 µm. The SBF interaction tests and tests of the simulated degradation confirmed the bioactive behavior of the prepared scaffolds and their ability to degrade under the simulated conditions. The scaffolds prepared by the direct foaming method showed better mechanical properties (compressive strength up to 1,8 MPa) than the scaffolds prepared by the template method. The results showed that the prepared scaffolds are suitable and promising for potential applications in bone tissue engineering.
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Sands for the production of foundry moulds and cores
Fúsek, Jakub ; Rusín, Karel (referee) ; Cupák, Petr (advisor)
Bachelor thesis deals with survey, properties and usability of the most common foundry molding sands. The most common sands are silicas for their economical. In particular, sands used in the Czech Republic are described, there is also a sand quarry with non-Europe distribution. Sadly, they have also many defects which limit to their use. In these cases we use non-silica sands. The most popular non-silica sands are outlined, including currently expanding synthetic sands. There are also listed some basic data and properties, for example, fitness for purpose.
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Determination of substances content in mint
Novotná, Martina ; Zlámalová Gargošová, Helena (referee) ; Vávrová, Milada (advisor)
This Bachelor thesis deals with determination of the content substances in mint (Mentha). Mint is in pharmacy very popular herb, it is been used for over 2000 years. We know many species of mint. Peppermint (Mentha piperita) is the most favorite and most common species. In the theoretical part there is description of substances found in plants, the characteristic of mint and principles of used analytical methods. Practical part of this thesis describes substances found in examined teas.
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Foundry sands and their properties
Odložil, Jan ; Nezvalová, Hana (referee) ; Rusín, Karel (advisor)
Bachelor thesis describes advantages and disadvantages of base sands used in foundries. The most popular base sands are silicas for their economical and size fraction. They have also much defects as discontinued heat dilatation, acidit reaction and silicosis. Non-silica base sands have not this disadvantages, but they are more expensive. Some foundries have started applying new synthetic non-silica base sands in recent time, which are chemically neutral and the casting quality is high.
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Development of method thermoporosimetry polymer powders
Urbánková, Radka ; Salajka,, Zdeněk (referee) ; Kratochvíla, Jan (advisor)
Thermoporosimetry is a technique to determine small pore sizes based on melting and crystallization point depression. The temperature shift was measured by Differential Scanning Calorimetry (DSC). Development of thermoporosimetry was carried out on silica with a well-characterized narrow pore size distribution. Several parameters were studied, which a have a direct influence on melting and crystallization point depression (for example: a quality of the solvent, filling the pores with the solvent, time and frequency of centrifuging, superfluous solvent removal conditions, etc.). The optimum conditions for the thermoporosimetry method were developed using high porosity silica. The optimized experimental conditions found for silica were applied to polypropylene powder with much lower porosity. Several polypropylene powders were synthesized using different polymerization catalysts and their porosity determined. Polymer powder morphology and structure was characterized by standard methods. Powder porosity obtained by thermoporometry, gas sorption, and BET methods was compared.
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Effect of colloidal silicon dioxide on selected properties of cement pastes and mortars
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The presented diploma thesis deals with the potential use of colloidal silica in cement composites. Investigation is focused primarily on selected properties of cement pastes and mortars with colloidal silica content. Two selected types of colloidal silica (particles with average size of 14 nm) have been used as a cement addition and partial replacement of cement, respectively. The experimental program for cement pastes with colloidal silica included tests for isothermal calorimetry (the study of cement hydration) and thermal analysis (determining the portlandite content). Hardened cement pastes have been studied through measurements of compressive strength. The microstructure was examined by scanning electron microscopy. Hardened mortars with colloidal silica have been studied through measurements of compressive strength, flexural strength, modulus of elasticity and fracture mechanics parameters. Fracture mechanics tests show that 5 % and 20 % addition of colloidal silica can enhance after 28 days of curing fracture energy up to 18,4 % and 32,7 %, respectively. For the compressive strength enhancing effect of colloidal silica, it was found to be more pronounced in the early age, while rate of strength gain can be lower than the control in the later ages. Our investigations revealed that the silica sol will coagulate immediately when the cement is mixed into the water containing sol. The ionic composition of pore fluid significantly influences the stability of colloidal silica and lead to their aggregation. After additional tests it has been found that small addition of calcium hydroxide greatly improved the compressive strength of the resulting cement pastes with colloidal silica content. Addition of calcium hydroxide in conjunction with modified cement paste preparation can enhance compressive strength after 3 days of curing up to 64,4 % in comparison with the blank paste.
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Highly porous ceramic materials prepared by Spark Plasma Sintering
Barančíková, Miriama ; Spusta, Tomáš (referee) ; Salamon, David (advisor)
Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.
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High purity silica materials: genesis, properties, and their potential resources in the Czech Republic
Tichý, Daniel ; Přikryl, Richard (advisor) ; Zachariáš, Jiří (referee)
Quartz and other siliceous materials are among the most widely used industrial raw materials. Demand for high-purity silica increased during past decades, specifically due to its growing use in the photovoltaic energy or electronic/electrical industries. Strict requirements on the purity of the feedstock, together with very complex processing technology, narrow down the choice of potential sources suitable for industrial extraction and use. This bachelor thesis provides an overview of the existing knowledge concerning the formation, properties, and processing of industrially exploitable deposits, and the market policy of high-purity quartz raw materials. This comprehensive overview is followed by a section that focuses on deposits and potential sources of high-purity quartz raw materials in the Czech Republic (Bohemian Massif). This part was elaborated on the basis of publicly available archival sources (final exploration reports or reserve calculations), available in the Czech Geological Survey - Geofond.
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Application of Electronic Continuum Correction to Molecular Simulations of Nano/Bio Interfaces
BIRIUKOV, Denys
Nowadays it is almost impossible to imagine our life without nanotechnologies. They are present in smartphones and many other gadgets we use every day, while advanced nanoparticle-based devises are currently indispensable in medicine, engineering, and science. In the case of biomedical applications, the knowledge how a specific nanomaterial behaves and changes its properties in complex physiological medium is essential to guarantee the accomplishment of all specific goals facing a scientist or engineer. Some of physical and chemical processes occurring when a nanodevice enters biological environment are yet very difficult to fully detail without accurate computer simulations, so special attention needs to be focused on theoretical studies of nano-bio interactions. In this thesis, molecular simulations were used to investigate the interactions between different nanomaterials (titanium dioxide, silicon dioxide, and gold) and aqueous solutions, which contain ions, organic molecules, and amino acids. The importance of this scope and particularly selected for this study materials and compounds is given in Introduction. To model nano/bio interfaces, we adopted and integrated recent theoretical approaches, which together with basic principles of molecular simulations are described in Methods. Obtained results are divided in four parts and address several important issues that are vital in deciphering molecular mechanisms, through which nanoparticles identify and bind various biomolecules. The simulation data are thoroughly discussed, compared to experiments, and used to explain some of experimental observations. Additionally, outcomes of this thesis serve as a springboard for further theoretical studies aimed to advance our understanding of nano-bio interactions.
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