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Study on kinetic stability of suspension with magnetorheological properties
Vlachová, Kristýna ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
Sedimentation in magnetorheological (MR) fluids is undesirable for many technological applications. For this reason, several ways have been proposed to prevent sedimentation instability. This thesis deals specifically with the addition of a suitable additive. The topic was examined based on available literature and according to it was suggested a procedure for the experimental part. Two types of MR liquids with different composition and preparation method were prepared. The first suspensions included a water-in-oil emulsion as a carrier liquid and Span 80 and Tween 80 as additives. For the second MR fluids, the continuous phase was a blend of bearing oils and the suspension was stabilized with organoclay. In both cases, carbonyl iron particles with a diameter of 1,8–2,3 µm were used. The kinetic stability of the prepared MR fluids was monitored and compared using an analytical centrifuge.
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Temperature dependence of carrageenan and hyaluronan solutions
Poledňáková, Halina ; Smilek, Jiří (referee) ; Hurčíková, Andrea (advisor)
This diploma thesis focuses on the study of temperature dependence of -carrageen, hyaluronan of low molecular weight (250–450 kDa) and hyaluronan of high molecular weight (1 500–1 750 kDa) in aqueous solutions. The description of temperature depending changes in properties of these substance is based on rheological method. This work concentrates on the characterization of viscoelasticity through measurement of the storage (elastic) and loss (viscous) modulus using -carrageen and hyaluronan solutions of different molecular weights and different concentrations depending on temperature (20–50 °C, alternatively, in carrageen, 20–80 °C). The temperature dependence was further measured using an uncommon technique called high resolution ultrasonic spectroscopy (HR-US) which measured relative velocity of selected concentrations of -carrageen and hyaluronan of high molecular weight depending on the temperature of heating and cooling (20–80 °C). The measurements of temperature dependence were carried out for varied oscillation frequencies of rheometer sensor/frequency of ultrasonic waves. Knowledge of temperature dependence of the investigated substances may be applied in drug chemistry, primarily with respect to degradation due to high temperatures. The measured data gives information about sol-gel temperature and gel-sol temperature of carrageen.
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Rheology as a powerful tool for the complex characterization of hydrogels
Kadlec, Martin ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
This diploma thesis investigates the suitability of relaxation tests as a part of complex characterization of hydrogel materials using classical rheology methods. With respect to the current research, creep and three interval thixotropy tests were taken into account. For them, general optimization was done aiming to find an ideal parameter settings. The optimization was performed using physically crosslinked agarose (AG) hydrogel and the tuned tests were also applied to two more samples: hyaluronan (HyA) and polyvinyl alcohol (PVAl) gel. These materials were selected due to their mutually different crosslinking principle. The experiments showed, the AG gel proved to have the best ability to recover after deformation of all studied samples. On the other hand, the HyA gel relaxed the worst. Although the final results of both tests were comparable, the regeneration process itself was different. Hence, the complex relaxation characteristics cannot be described using one of the performed tests alone and both the creep and three interval thixotropy tests have great importance in the scope of complex relaxation behaviour. The obtained results may lead to more precise description of deformation and relaxation, which are frequent phenomena occurring during treatment and application of hydrogel materials.
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Composting of biodegradable polymers
Hollá, Tereza ; Smilek, Jiří (referee) ; Obruča, Stanislav (advisor)
This master’s thesis deals with the study of composting of polyhydroxybutyrate (PHB) and polylactic acid (PLA). The experimental part focuses on the composting test based on the IS/ISO 20200 standard, in which biopolymers were degraded within 8 weeks. The advantage of the composting test was the unique use of bags for polymer granules, which simplified the handling of samples. The placement of the polymers ensured an even load of compost, which simulated the landfill environment, which also made this experiment exceptional. The use of different methods of analysis ensured the investigation of the influence of compost on the degradation of polymers, but also the influence of polymers on the compost microbiome. In the compost environment all of the studied polymers degraded. After 8 weeks the weight loss of approximately 40 % was detected in PHB. Amorphous PLA degraded completely in the 5th week of experiment, while semicrystalline PLA lost approximately 70 % of its weight in 8 weeks. Using SEM images and SEC analysis, we conclude that PHB degradation was predominantly biological. Degradation of PLA samples was found to be predominantly abiotic. Analysis of compost samples revealed that the enzymatic activity of esterases increased in composts with polymers compared to compost without polymers. The effect of polymers on the microbiome in compost was analyzed using Biolog EcoPlates™. Compost with PHB showed a high ability to adapt to various substrates and microbiome expanded during composting. In the case of a sample with semicrystalline PLA, it was found that in the last week of composting, the ability of microorganisms to adapt and use substrates decreased, which indicates a possible negative effect of this polymer on compost development.
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Utilization of advanced rheological techniques for the study of biological systems
Krňávková, Šárka ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
A new method for determining viscoelastic properties on the interfacial interface called interfacial rheology was intoduced and investigated. Measured data were compared with data from tanziometer for model system of surfactant. Three concentration renge of surfactant, namely SDS (anionic), TTAB (cationic) and Tween (nonionic), were measured. From the measured data the influence of structure, critical micellar concentration and charge on the viscoelastic properties of the interfacial interface was determined. Furthermore, this new method was used for biological systems and specifically for biofilms of two bacterial strains. First, the viscoelastic properties of biofilms on the agar were determined, and the viscoelastic properties dependence on temperature
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Structural aspects of interaction between humic substances and charged organic xenobiotics
Prisažný, Adam ; Smilek, Jiří (referee) ; Sedláček, Petr (advisor)
This diploma thesis was focused on studying the interaction of humic substances with ionic organic xenobiotics and its structural aspects. The method was chosen from my bachelor thesis, steady-state fluorescence spectroscopy, which is suitable for substances with weak fluorescence. The results showed that the interaction between humic acids and representatives of ionic organic xenobiotics (Septonex) was reflected in fluorescence quenching of humic acids and the shift of emission maximum to lower wavelength, hypsochromic (blue) shift. From the measurement results, we can assume that the interaction that is formed between the aromatic structures in humic acids and Septonex could be -cation interaction.
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Preparation and characterization of magnetorheological suspensions with high sedimentation stability
Oharek, Lukáš ; Krouská, Jitka (referee) ; Smilek, Jiří (advisor)
The introduced diploma thesis focuses on the preparation of magnetorheological suspensions with high sedimentation stability. The theoretical part generally describes these suspensions and their properties, it also focuses on the possibilities of improving sedimentation stability, for example by modifying the surface of the particles or adding additives. A research based on the topic of preparation of sedimentation stable magnetorheological suspensions was also carried out. The experimental part focuses on two types of magnetorheological suspensions. The first type of suspension consisted of a water-in-oil emulsion and carbonyl iron particles that were modified by chemisorption of the surfactant Tween 80. Another type of suspension contained thixotropic organoclay along with untreated iron particles. In both types of magnetorheological suspensions, the process of their preparation was optimized, together with the composition of carrier fluids for the preparation of the most sedimentation-stable magnetorheological suspension. The measurement of sedimentation stability by a dispersion analyser confirmed the positive effect of particle modification and the addition of thixotropic agent on the sedimentation stability of suspensions.
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Influence of molecular weight of polymers on phase-separated hydrogels
Kolomá, Nikola ; Smilek, Jiří (referee) ; Mravec, Filip (advisor)
This work is focused on study of individual systems of hyaluronan mixtures. All mixtures of hyaluronans they were ready at molecular weights of 15-30 kDa, 80-150 kDa, or 1500-1750 kDa. These individual molecular weights were combined in different ratios most often in ratios of 70:30, 50:50 and 30:70. Septonex surfactant was used for all mixed samples and CTAB was used for last experiment too. At first the gel samples were prepared by a dry route of individual powders with accurately calculated batches. All solutions were prepared wet route with stock of exactly calculated concentration. Physical gels were prepared by combinations of Septonex and hyaluronan with the different molecular weights. In solution formed irregular shapes which we could describe as "marbles" or "beads". After the sample was to stand, the individual „marbles“ of the gel were formed whole mass. Was done too many experiments with physical gels, which has been carried out behavior of mixtures hyaluronans with different molecular weights. All physical and chemical properties were observed by the eye, described and in the and were photographed. Was used hydrophil dye in experiments and served for better visualize comparison samples between themselves. The last experiment was rheological measurement with which is possible characterize viscosity od individual samples.
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Study on interaction of humic substances with surface active agents
Bělušová, Anna ; Krouská, Jitka (referee) ; Smilek, Jiří (advisor)
This bachelor thesis deals with the study of interactions between humic acids (HK), as the main component of soil organic matter, and model pollutants in the form of surfactants through unconventional and original combination of dialysis and diffusion techniques. Since dialysis techniques are rarely used for the interaction of humic substances with surfactants study, it was necessary to optimize methods for determining of ionic surfactants (cationic Septonex and anionic sodium dodecylsulfate were selected as representatives) prior to begining of own experiments, using a method based on the color ion pair creation between a surfactant and a counter-charged dye, followed by this pair extraction into an organic solvent. Diffusion cell dialysis experiments were performed with cationic surfactant Septonex, which was expected to interact positively with humic acids relative to its charge. As humic acids representatives, the standards of these substances provided by the International Society for Humic Substances (IHSS) were selected, namely humic acids (IHSS HK) isolated from Leonardite (1S104H). One of this bachelor thesis aims was to verify the effect of carboxylic functional acids on reactivity and barrier abilities of humic acids. For this reason, these standards have been modified by the selective methylation of carboxyl groups which no longer participate in the interaction with surfactants. Already from the first experiments there was a noticeable decrease in the concentration of Septonex over time – it means its transition through the dialysis membrane to humic acids, which indicates a positive affinity of humic acids to Septonex. The extent of these interactions was assessed through the apparent interactions parameter app through which the assumption that IHSS HK reacted with Septonex more than their methylated form of MIHSS HK was verified.
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