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Alternative crosslinking methods for sodium alginate resulting in hydrogels with suitable application properties
Kouřilová, Ludmila ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
This diploma thesis is focused on the preparation of alginate gels with the potential to influence their final application properties (transparency, syneresis, viscoelastic properties, etc.). Based on literature review, a total of three gelation strategies leading to the gelation of sodium alginate were selected, namely ionotropic gelation by external gelation method, ionotropic gelation by internal gelation method, and alginate crosslinking with phytic acid, which is capable of forming both ionic bonds and intramolecular hydrogen bonds. Subsequently, the preparation of alginate gels was optimized, their mechanical properties were characterized, and finally, the influence of several factors (polymer concentration, amount of crosslinking agent, gelation time, addition of sucrose, etc.) on the resulting properties of the prepared gels was monitored. Within the scope of the thesis, it was demonstrated that the resulting properties of sodium alginate-based gels are influenced not only by the polymer concentration, the amount of crosslinking agent used, gelation rate, or syneresis, but in the case of ionotropic gelation by external gelation, for example, also by the type of anion used. An interesting part of the thesis is also the optimization of determining the mechanical properties of alginate gels through compression tests. During these tests, the sample is compressed between two rheometer sensors, and the mechanical response of sample to the applied force is measured. It is one of the most easily conceivable rheometric tests.
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Viscoelastic properties of hydrogels depending on relative humidity
Kouřilová, Ludmila ; Heger, Richard (referee) ; Smilek, Jiří (advisor)
This bachelor thesis is mainly aimed on the determination of the dependence of the viscoelastic properties of physically crosslinked hydrogels on the relative humidity controlled by humidity cell (as an accessory to a rotary rheometer), or the desiccator with the drying medium. The main objective was to optimise the methodology of the humidity cell for the rheological determination of the viscoelastic properties of hydrogel materials as a function of relative humidity and to verify experimental setup on the agarose hydrogel. The results showed that the agarose hydrogel gradually loses its dispersion medium after exposure to chosen relative humidity, resulting in a loss of contact between the upper rheometer sensor and the sample when measured with the standard measurement gap control setting, which is constant during the measurement. The setting of the control of normal force proved to be an appropriate solution, which has led to a gradual reduction in the height of the upper rheometer sensor in an attempt to keep the normal force at the desired level during the drying of the hydrogel. A humidity cell proves to be an appropriate method for determining the dependence of the viscoelastic properties of hydrogels on relative humidity. Unlike the use of a desiccator with drying medium, the drying of the hydrogel sample does not result in such rapid drying that it breaks the texture on its surface. Another advantage of a humidity cell is the ability to maintain the desired relative humidity value even if the gel begins to release dispersion medium into its surroundings, which was not possible with a desiccator with drying medium.
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Viscoelastic properties of hydrogels depending on relative humidity
Kouřilová, Ludmila ; Heger, Richard (referee) ; Smilek, Jiří (advisor)
This bachelor thesis is mainly aimed on the determination of the dependence of the viscoelastic properties of physically crosslinked hydrogels on the relative humidity controlled by humidity cell (as an accessory to a rotary rheometer), or the desiccator with the drying medium. The main objective was to optimise the methodology of the humidity cell for the rheological determination of the viscoelastic properties of hydrogel materials as a function of relative humidity and to verify experimental setup on the agarose hydrogel. The results showed that the agarose hydrogel gradually loses its dispersion medium after exposure to chosen relative humidity, resulting in a loss of contact between the upper rheometer sensor and the sample when measured with the standard measurement gap control setting, which is constant during the measurement. The setting of the control of normal force proved to be an appropriate solution, which has led to a gradual reduction in the height of the upper rheometer sensor in an attempt to keep the normal force at the desired level during the drying of the hydrogel. A humidity cell proves to be an appropriate method for determining the dependence of the viscoelastic properties of hydrogels on relative humidity. Unlike the use of a desiccator with drying medium, the drying of the hydrogel sample does not result in such rapid drying that it breaks the texture on its surface. Another advantage of a humidity cell is the ability to maintain the desired relative humidity value even if the gel begins to release dispersion medium into its surroundings, which was not possible with a desiccator with drying medium.
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