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...

CHARLES UNIVERSITY Faculty of Pharmacy in Hradec Kralove Department of Pharmaceutical technology Name: Klára Tenorová Title of diploma thesis: Thixotropy test of semisolid preparations Supervisor: PharmDr. Eva Snejdrova, Ph.D. This thesis deals with the study of thixotropic properties of selected semi-solid preparations such as Vaselinum album, Adep lanae, Adeps lanae cum aqua, Alcoholis cetylici unguentum and Alcoholis cetylici cremor. The theoretical part deals with characterization of semi-solid preparations and ointment bases, rheology, rheometry and description of the tests used in the measurement. The experimental part deals with the description of viscosity curves and with the measurement of time dependency of flow behaviour by thixotropic test. Model semi-solid samples show only partial recovery, i.e. false thixotropy. The highest recovery of the structure was shown by Adeps lanae, 83 % at 25 řC and 79 % at 32 řC. The flow behaviour are changed by incorporation of the water depending on the character of the semisolid preparation. At 25 ř C, the viscosity recovery rate was lower than at 32 ř C for all samples except Adeps lanae. After the emulsification of 25% water to Adeps lanae, the recovery rate at both temperatures was significantly reduced, which means that lanolin is slower to recover...

Materials such as asphalt, polymers or the Earth's crust tend to behave in a way that can be described neither with a model of viscous fluid, nor a model from solid mechanics. There are indeed models capable of capturing these so called viscoelastic phenomena far better, but they are based on the presumption of constant temperature. In many cases, e.g. in the glass industry or in geophysics, the properties of a viscoelastic material strongly depend on temperature. That is why it is precisely these changes that need to be described. There are viscoelastic models used in practice that take into account the material parameters' dependence on temperature, however, they do not consider the viscoelastic nature of the material when describing the temperature evolution. The objective of this thesis is to derive thermodynamically consistent viscoelastic models with temperature dependent parameters and the appropriate evolution equation for temperature, implementation of the models and computing simple test simulations. Powered by TCPDF (www.tcpdf.org)

Heat-treatment belongs to the most ecological methods of wood preservation methods and increase of its natural stability in exposition to outdoor conditions. Research of mechanical properties opens new possibilities of thermowood usage in general. Wood appertains to viscoelastic materials and due to long-term loading creeps. There currently rise both elastic deformation, deformation elastic in time and plastic deformation. Partially there are irreversible changes due to stress even after unloading. This work presents first insight to the matters of thermowood rheology and inspects its behavior under long-term loading in bending. This paper compares ratio of these three types of deformation in untreated wood and thermally modified wood in seven different temperatures (140; 160; 180; 190; 200, 210°C). The samples were exposed to 600 hours applied loading covering 40% of ultimate stress (modulus of rapture). Test were performed under constant conditions in special creep units in conditioning kiln. Increasing deformation under constant load was analyzed by Burger rheological model. The results show that samples treated under lower temperatures (140 and 160°C) exhibit greater creep than untreated wood. This result is positive for structural usage of wood. On the other hand the samples treated under higher temperatures levels (200 an 210°C) display deterioration of mechanical properties. This is due to changes in wood structures caused by heat-treatment. The most important impact of this work goes to future research of this field. Next development has to apply for the best quality of samples and also select rather prismatic parallelism than transversal one. Also application of 40% ultimate stress loading appeared as too high and together with wood defects led to destruction of samples.

Title: Maxwell-type viscoelasticity in small and large deformations of planetary mantles Author: Mgr. RNDr. Vojtěch Patočka Department: Department of Geophysics Supervisor: prof. RNDr. Ondřej Čadek, CSc., Department of Geophysics Abstract: A present limitation of global-scale simulations of planetary interi- ors is that they assume a purely viscous or viscoplastic flow law for solid rock, i.e. elasticity is ignored. This is not a good assumption in the cold and strong outermost mantle layer known as the lithosphere, which seems to maintain its elastic properties even on time scales corresponding to the geological processes of subduction or sedimentation. Here we overcome such simplification and present a numerical tool for modelling visco-elasto-plastic mantle convection. The most promising new feature of the resulting models is related to the ability of vis- coelastic materials to remember deformation experienced in the past. Thus, the growing viscoelastic lithosphere of a cooling planet, when subject to internal or surface loading, can store information about its thickness at the time of loading. This phenomena is consistent with datasets of the effective elastic thicknesses determined in flexure studies and we label it here as the "stress memory effect". Attention is also paid to the theoretical foundations...

Poddajné kontakty obsahující polymerní nebo pryžové členy lze nalézt v technických i biologických aplikacích. I přes vývoj v této oblasti existují efekty, které ovlivňují tribologické aspekty těchto kontaktů, a je třeba je dále zkoumat. Tato práce se zabývá vlivy kinematických podmínek, konfigurace, viskoelasticity a viskozity maziva na tření v mazaných poddajných kontaktech. Výsledky byly použity k vývoji numerického modelu pro predikci kapalinového tření v poddajných kontaktech. K objasnění chování poddajných kontaktů bylo použito zařízení Mini Traction Machine (MTM) v konfiguraci ball-on-disc, což umožnilo zkoumání zmíněných vlivů. Z poznatků z technické oblasti bylo zjištěno, že viskoelasticita se projevuje ve všech konfiguracích, tedy soft-on-hard, hard-on-soft a soft-on-soft, a její efekt je nejvýznamnější v konfiguracích s poddajným diskem. Data dále ukazují, že poměr skluzu a valení má vliv na valivé tření což je v rozporu se současnou literaturou. Výsledky z biologické oblasti naznačují, že za určitých podmínek lze nahradit nativní kapalinu jednoduchým mazivem. Tyto poznatky mohou posloužit jako odrazový můstek pro další studie zabývající se poddajnými kontakty.

The aim of my graduation theses is to work up the literature search of polymer processing. To give a short summary of their structure, characteristic and fabrication technique. Then to make a structural design of injection mold for producing the scheduled aim and motivate this design with requisite calculation for construction of the tool, a choice of injection machine and rundown of injection cycle. At the end of my work is this aim economically reviewed and compared with alternative form of structural design.

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.

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.

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