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Viscoelastic properties of ferrofluid - Study of normal stresses differences
Šustková, Hana
Since 1960, a liquid becoming strongly magnetized in the presence of a magnetic 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. According 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 for shear experiment is found to be much stronger than in shear direction. In dynamical mode, the...
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Viskoelastická deformace v geofyzikálních aplikacích
Sládková, Kateřina ; Čadek, Ondřej (advisor) ; Průša, Vít (referee)
Our aim was to aid the viscoelasticity into the model for thermal convection by developing our own code in Fortran 90 and to study the role of viscoelasticity in this model. We should have included the viscoelasticity by Maxwell model; however, due to numerical instability we changed it for Oldroyd-B model. We were adding the terms of objective derivative into our code step by step and we were observing how they influence the behaviour of thermal convection. Partial time derivative and advective terms were included in whole complexity, the corrotational terms need more numerical testing. Our work suggest that the influence of viscoelasticity on thermal convection is noticeable. Powered by TCPDF (www.tcpdf.org)
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: Viscoelasticity of bones - the methodology of measurement
Cihlář, Zdeněk ; Ďoubal, Stanislav (advisor) ; Kuchařová, Monika (referee)
Charles University in Prague, Faculty of Pharmacy in Hradec Králové Department of biophysics and physical chemistry Candidate: Mgr. Zdeněk Cihlář Supervisor: Prof. RNDr. Ing. Stanislav Ďoubal, CSc. Title of Thesis: Viscoelasticity of bones - the methodology of measurement The aim of the thesis was to verify the methodology of measuring the viscoelastic parameters of human bones using an apparatus enabling the measurement of dynamic characteristics. The method is based on measurement of deformation response of samples to short or rectangular impulse of force. The samples were obtained from femoral head. The methodology is therefore based on measuring of creep curves and impulse characteristics. Resulting damped oscillations were analysed. The transient and impulse characteristics in bending stress and twisting stress were obtained. Based on these characteristics, viscoelastic parameters of samples were determined (Young modulus, shear modulus and viscosity). The Poisson's number, indicating the ratio of transverse contraction to longitudinal extension of the material during deformation, was calculated using the values of Young's modulus and shear modulus. The measured values of the Young's modulus in bending stress vary in the range from 62MPa to 670MPa. The values of the shear stress modulus range...
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Utilization of interfacial rheology to study of biological systems
Kachlířová, Helena ; Kalina, Michal (referee) ; Smilek, Jiří (advisor)
The aim of this bachalor thesis is to implement and optimization a relatively new method of interfacial rheology. The optimization of this method was realized on two types of interfaces, specifically liquid-liquid using immiscible systems water-chloroform and water-toluene, and water-air. The applicability of this method was tested by using real samples in form of surfactant septonex and biological system represented by protein (bovine serum albumin). The interfacial layers formed by septonex were purely viscous, where the rigidity of the layer increased slightly with concentration until reaching critical micellar concentration and then the rigidity decreased. In comparison with septonex, the interfacial film made of bovine serum albumin showed predominantly elastic behaviour.
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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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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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The motion of a fluid with pressure dependent material moduli under a surface load
Janečka, Adam ; Průša, Vít (advisor) ; Čadek, Ondřej (referee)
In the present work, we study the motion of homogeneous, isotropic, incompressible fluid with viscosity depending on the pressure. The motion is studied in a infinite domain under a surface load by a prescribed pressure on one of the boundaries. This so called free boundary is due to the exerted pressure deformed and is also subject of study. After an acceptable simplification and prescribing suitable boundary conditions, the problem is solved at first analytically using the perturbation method, then numerically by means of the spectral methods. The effort is to observe any differences in the motion in comparison to commonly used Newtonian fluid.
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Identification of complex modulus using of the Hopkinson Split Pressure Bar.
Buchar, J. ; Trnka, Jan ; Řídký, R.
A split Hopkinson pressure bar procedure was used for non-parametric identificon of complex\nmodulus under conditions of non-equilibrium and axially non-uniform stress Tests were carried out with\naluminium bars and with specimens of composite materials (Low viscosity epoxy resin and Baytube multiwalled\ncarbon nanotubes) and having diameter 15 mm and length 7 mm. The influence of the nanotubes\nconcentration on the dynamic response of given composites was evaluated.
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Microrheology of Biocolloids
Hnyluchová, Zuzana ; Omelka, Ladislav (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
The main aim of the doctoral thesis was study of passive microrheological techniques as advanced methods for characterisation of viscoelastic properties of soft material. These techniques are able to provide certain advantaged or additional information on classical rheology. Several techniques from the wide range of passive microrheological group such as one particle video – microrhelogy with IDL data procesing, microrheology based on light scattering – DLS or FCS microrheology have been applied in practice during my PhD studies. New Matlab script has been also invented to simply obtain information about viscosity of low volume samples. Aplicability of techniques were studied on several various bicolloids such as solutions or gels of hyaluronic acid, on study of properties at the interfaces or on gelation proces studies of agarose. Obtained data were compared classical rheology results. Suitability of each technique for investigated systems or appropriate reccomendations for further measurements were didcussed based on obtained data. Main advantages and limites of passive microrheology techniques were also described in comparison wih classical rheology method.
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Kinetics Studies of Collagen I Self-Assembly
Voldánová, Michaela ; Ondreáš, František (referee) ; Jančář, Josef (advisor)
Collagen, the most abundant protein of connective tissues, in various forms has a wide applications due to their diverse biological and chemical properties. One of the forms are collagen hydrogels, which are considered very suitable material for applications in tissue engineering, because they are able to provide biodegradable scaffolds that its properties correspond with living tissues. These systems are used for example as scaffold for targeted drug delivery with controlled release, in combination with cells can be used for the regeneration and reconstruction of tissues and organs. Heating the aqueous solution of collagen leads to spontaneous self-assembly process to variously distributed fibrillar structures, which are at a later stage of fibrillogenesis prerequisite for creating a three-dimensional supporting network, which is the basic building block of the gel. The resulting properties of the hydrogel depend not only on its structure, but also on the conditions which cause self-assembly process. Hydrogels were performed at 37 ° C and physiological pH. Studied structural variable was the concentration of collagen. So far, for the research of self-assembly were used spectrometric methods, which only provide information about kinetics of morphogenesis. In this work to study the kinetics of collagen I self-assembly were used rheological methods, which additionally give information about viscoelastic properties of the resulting material. The obtained experimental data confirmed two-step process of collagen I fibrillogenesis consisting of nucleation and growth process. Rheological hydrogels collagen behaved as a nonlinear yield-pseudoplastic. An attempt was made to molecular interpretation of the results. Using two-parametric Avrami equation was determined the rate of self-assembly for each concentration of collagen and the value of Avrami exponent determining the shape of produced units. The prepared hydrogels were subjected to increasing shear stresses (strain amplitude, shear rate). Larger amplitudes leads to collapse of the hydrogel structure, which is able to again partially regenerated.
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