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Smart hybrid gels
Strachota, Beata Katarzyna ; Matějka, Libor (advisor) ; Matějíček, Pavel (referee) ; Krakovský, Ivan (referee)
This Thesis is dedicated to the development of mechanically reinforced thermoresponsive hydrogels, able of fast and extensive temperature-induced volume transition. Poly(N-isopropylacrylamide)- (PNIPA-) based hydrogels crosslinked with Laponite clay nano-platelets, which are known for their extraordinary mechanical properties, were synthesized by free radical polymerization of the NIPA monomer in the presence of exfoliated clay nanoplatelets. In this work, the crucial role of the employed redox initiators in the formation of the physical PNIPA/clay network was established, and the particular processes taking place during the polymerization and network structure formation were described. The correlation of the time-dependent NIPA monomer conversion and of the observed structure-formation stages made possible to propose a general mechanism of the PNIPA/clay hybrid gel formation. Generally, a considerable attention was paid to the investigation of the formation-structure-property relationships. This knowledge makes it possible to control the structure evolution and hence the final material properties of the gels. An important part of this work is dedicated to the study of mechanical properties of the PNIPA/clay nanocomposite hydrogels and of the parameters which control them. The gained knowledge of...
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Viskoelastické vlastnosti ferrokapaliny - Studium normálových napětí
Šustková, Hana ; Krakovský, Ivan (advisor) ; Filip, Petr (referee)
Viscoelastic properties of ferrofluid - Study of normal stresses differences Master Thesis Hana Šustková Abstract: Since 1960, a liquid becoming strongly magnetized in the presence of a mag- netic field, called ferrofluid, is known. This colloidal liquid made of ferro- or ferrimagnetic nanoparticles, with diameter in range 10-20 nm, suspended in a carrier fluid. This work focuses on the study of the viscoelastic properties of a selected ferrofluid - the steady-state and dynamic properties of the fluid with comparison to a standard fluid (basis fluid, etc.) and a MR fluid. Rheological measurements are carried out using a commercial rheometer. A magnetic cell for this rheometer is designed and built. In this magnetic cell the experiments are realized, the whole system is calibrated and the experiments performed. The ferrofluid APG513a, MR-fluid and reference fluid were used. Study of normal stresses differences (N1,N2) in liquids is carried out. Ac- cording to derived theoretical model, the course of N1 and N2 should be strongly dependent on the field - this was studied directly by measuring of the normal forces or indirectly applying the Laun's rule. A good accordance of theory and experiment was found and an anisotropic behaviour of ferrofluid was studied. The shear-thinning ability of the ferrofluid in normal direction...
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Smart hybrid gels
Strachota, Beata Katarzyna ; Matějka, Libor (advisor) ; Matějíček, Pavel (referee) ; Krakovský, Ivan (referee)
This Thesis is dedicated to the development of mechanically reinforced thermoresponsive hydrogels, able of fast and extensive temperature-induced volume transition. Poly(N-isopropylacrylamide)- (PNIPA-) based hydrogels crosslinked with Laponite clay nano-platelets, which are known for their extraordinary mechanical properties, were synthesized by free radical polymerization of the NIPA monomer in the presence of exfoliated clay nanoplatelets. In this work, the crucial role of the employed redox initiators in the formation of the physical PNIPA/clay network was established, and the particular processes taking place during the polymerization and network structure formation were described. The correlation of the time-dependent NIPA monomer conversion and of the observed structure-formation stages made possible to propose a general mechanism of the PNIPA/clay hybrid gel formation. Generally, a considerable attention was paid to the investigation of the formation-structure-property relationships. This knowledge makes it possible to control the structure evolution and hence the final material properties of the gels. An important part of this work is dedicated to the study of mechanical properties of the PNIPA/clay nanocomposite hydrogels and of the parameters which control them. The gained knowledge of...
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Organic-Inorganic Polymer Nanocomposites
Ponyrko, Sergii ; Matějka, Libor (advisor) ; Krakovský, Ivan (referee) ; Zelenka, Jiří (referee)
The epoxy based polymer is one of the very common polymers, which was used as a host to create new better materials - nanocomposites. This thesis focused on the improvement of the thermomechanical properties of the epoxy thermosets without deteriorating their existing benefits and on further potential application of this knowledge in "smart" systems. The largest part of this work is dedicated to the reinforcement of epoxy thermosets by in situ generated silica and synthesis of organic-inorganic nanocomposites. Borontrifluoride monoethylamine (BF3MEA) was chosen as effective catalyst for the formation of nanosilica in epoxy-amine network matrix under nonaqueous (non-hydrolytic) sol-gel process. We proposed the mechanism of the nonaqueous sol-gel procedure, studied the structure evolution during the nanocomposite formation, and also determined the structure, morphology and thermomechanical properties of the obtained epoxy-silica nanocomposites. Significant attention in this work was given to the application of coupling agent and ionic liquids to improve compatibilization of the organic matrix and the inorganic part. As a result of the nonaqueous sol-gel process optimization by combination of the tetramethoxysilane (TMOS) and the coupling agent glycidyloxypropyltrimethoxysilane (GTMS), the high-Tg and...
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Viskoelastické vlastnosti ferrokapaliny - Studium normálových napětí
Šustková, Hana ; Krakovský, Ivan (advisor) ; Filip, Petr (referee)
Viscoelastic properties of ferrofluid - Study of normal stresses differences Master Thesis Hana Šustková Abstract: Since 1960, a liquid becoming strongly magnetized in the presence of a mag- netic field, called ferrofluid, is known. This colloidal liquid made of ferro- or ferrimagnetic nanoparticles, with diameter in range 10-20 nm, suspended in a carrier fluid. This work focuses on the study of the viscoelastic properties of a selected ferrofluid - the steady-state and dynamic properties of the fluid with comparison to a standard fluid (basis fluid, etc.) and a MR fluid. Rheological measurements are carried out using a commercial rheometer. A magnetic cell for this rheometer is designed and built. In this magnetic cell the experiments are realized, the whole system is calibrated and the experiments performed. The ferrofluid APG513a, MR-fluid and reference fluid were used. Study of normal stresses differences (N1,N2) in liquids is carried out. Ac- cording to derived theoretical model, the course of N1 and N2 should be strongly dependent on the field - this was studied directly by measuring of the normal forces or indirectly applying the Laun's rule. A good accordance of theory and experiment was found and an anisotropic behaviour of ferrofluid was studied. The shear-thinning ability of the ferrofluid in normal direction...
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Measurement and evaluation of elongational viscosity of selected biomaterials
Šustková, Hana ; Krakovský, Ivan (advisor) ; Fortelný, Ivan (referee)
Measurement and evaluation of elongational viscosity of selected biomaterials Bachelor thesis abstract Hana Šustková 20.5.2011 This thesis analyzes the elongational viscosity of the biomaterials. The basic concepts related to the issue of measurement of shear and elongational viscosity of melts in particular focusing on the SER rheometer, which was used in the experiment, were presented. With SER rheometer elongational viscosity of BioFlex samples of BioFlex, PA6 and their mixtures at temperatures of 225o C and 235o C for ten Hencky different strain rates from 0.1 to 10 s−1 were studied. In the experiment rectangular specimens prepared for different content of Bioflex and Polyamide PA6 were used. Based on the data presented in this thesis some features of the internal structure of used bio- material, and its possible practical applications, further and qualitative changes in its properties in the mixture were described. It was shown that the linear viscoelastic response of BioFlex is two orders of magnitude below in comparison to the response of PA6 and in the temperature range the linear viscoelastic response does not change. It is shown that in mixtures with BioFlex and PA6 the BioFlex shows a signifi- cant proportion of the linear viscosity range - and at low concentrations of BioFlex in comparison to PA6...
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Structure and properties of nanophase separated hydrogels
Lungová, Marta ; Hanyková, Lenka (referee) ; Krakovský, Ivan (advisor)
A central goal of this work is study of structure and mechanical and thermal properties of hydrogels prepared by swelling of hydrophilic polymer networks in water. To this purpose series of epoxy networks was prepared by reaction of ,- diamino terminated poly(oxypropylene)-b-poly(oxyethylene)-b-poly(oxypropylene)- with aromatic diepoxide (Bisphenol A propoxylate diglycidyl ether). Network formation process was monitored by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Nanophase separation in the networks prepared has not been found by dynamic mechanical analysis (DMA) or differential scanning calorimetry (DSC). On the other hand, nanophase separated structure of the hydrogels has been revealed by small-angle neutron scattering (SANS). SANS data were fitted well using Teubner-Strey model based on the locally lamellar structure of water-rich and water-poor nanodomains and values of model parameters are determined. Formation of nanophase separated structure is attributed to high difference in the interaction of network components with water. Influence of water on thermal transitions in hydrogels is studied by DSC.
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