Diese Doktorarbeit untersucht die verschiedenen dynamischen Prozesse, welche sich an der Tropfenoberfläche abspielen, und der Methoden, die für deren Untersuchung verwendet wurden. Das Ziel dieser Arbeit ist es, die entscheidenden Eigenschaften, die einen Einfluss auf das mechanische Verhalten der Grenzfläche haben, zu identifizieren. Wir verwenden die hydrodynamisch erzwungene Deformation eines Tropfens in einem Mikrokanal, um die mechanischen Eigenschaften der Oberfläche zu untersuchen. Diese Methode wird auf drei verschiedene Fälle angewendet. Als erstes verfolgen wir die zeitliche Entwicklung einer Grenzflächenverformung, um die Dynamik der Tensidadsorption an einer Oberfläche zu untersuchen. Dabei kalibrieren wir die Tropfenverformung als Funktion von Tropfengröße und Oberflächenspannung. Diese Technik wird auf den Fall eines perfluorierten Tensids, welches von industriellem und wissenschaftlichem Interesse ist, angewendet. Wir zeigen die Möglichkeit von Messungen der dynamischen Oberflächenspannung auf Zeitskalen von zehn Millisekunden und gewinnen daraus kinetische Eigenschaften der Moleküle. Wir vergleichen die Dynamik, welche mit der klassischen Pendant-Drop-Methode gemessen werden kann mit denen der Mikrofluidik. Es zeigt sich, dass die Adsorption für den Pendant Drop von der Di usion begrenzt wird, während in der Mikrofluidik die Anbindung an die Oberfläche der langsamere Prozess ist. Der Unterschied entsteht durch das Flussprofil in der Mikrofluidik, welches konvektiven Transport induziert. Danach untersuchen wir die Verformung unter verschiedenen räumlichen Beschränkungen im mikrofluidischen Kanal. Die Tropfenverformung wird mit einer zweidimensionalen numerischen Simulationen und mit einem dreidimensionalen Modell eines Rotationsellipsoids verglichen. In beiden Fällen wird eine qualitative Übereinstimmung festgestellt, jedoch existieren auch spürbare Abweichungen vom Experiment. Die Abweichungen vom zweidimensionalen Modell ist erklärbar mit dem sinkenden Einfluss der viskosen Spannungen mit der Kanalhöhe, hervorgerufen durch Beiträge von Deformationen außerhalb der Beobachtungsebene, welche von dem Modell nicht wiedergegeben werden. Die Abweichungen vom dreidimensionalen Modell kommen von den räumlichen Beschränkungen, welche die Tropfenform von einem Rotationsellipsoid abweichend verformt. Die Untersuchung zeigt die Schwierigkeiten bei der Beschreibung von viskosen Kräfte für Abmessungen, die zu groß sind um als zweidimensional betrachtet zu werden, aber wo die Wechselwirkungen mit den Kanalwänden nicht vernachlässigbar sind. Wir diskutieren ebenfalls den Fall der trägen Relaxation des Tropfens bei Reynoldszahlen von Re 10, für welchen Oszillationen der Tropfenoberfläche beobachtet werden. Wir zeigen, dass die Oszillationen als hydrodynamische Analogie zu einer hookeschen Feder beschrieben werden können, wobei die Oberflächenspannung als Federkonstante fungiert und die Dämpfung durch die Viskosität der Flüssigkeit bestimmt wird. Die Methode liefert korrekte Ergebnisse sowohl für reine Grenzflächen als auch für Grenzflächen mit Tensiden, was zu einer zusätzliche Möglichkeit führt, die Oberflächenspannung aus der Frequenz der Verformungen zu bestimmen. Die viskose Relaxation wurde auch hierbei von den Kanalwänden beeinflusst. Als letztes wenden wir die Methode der mikrofluidischen Tensiometrie auf die Kinetik einer Polymerisationsreaktion auf der Tropfenoberfläche an. Der Einfluss der Reagenzkonzentration auf die Reaktionszeit wird untersucht, ebenso wie der E ekt der Gegenwart von Tensidmolekülen. Erste Ergebnisse dieser Untersuchung zeigen, dass die Deformation einer komplexen Grenzfläche nicht mehr allein durch die Oberflächenspannung beschrieben werden kann. Vielmehr muss die Beschreibung der mechanischen Eigenschaften der Grenzfläche notwendigerweise die Entstehung der Viskoelastizität an der Oberfläche mit in Betracht ziehen. Diese Erkenntnis erö net neue Möglichkeiten, mit Hilfe von Mikrofluidik die mechanischen Eigenschaften von komplexen Grenzflächen, wie zum Beispiel kolloidbesetzte Grenzflächen oder Membranen, zu charakterisieren.

The study of asphalt chemo-mechanics requires a basic understanding of the physical properties and chemical composition of asphalt and how these properties are linked to changes in performance induced by chemical modifications. This work uniquely implements the framework of chemo-mechanics by investigating two types of chemical modification processes, natural (oxidative aging) and synthetic (chemical doping) as they relate not only to macro-scale properties of asphalt binder but also to the asphalt microstructure and nanorheology. Furthermore, this study demonstrates the application of atomic force microscopy (AFM) imaging and the extraction of nano-scale engineering properties, i.e. elastic modulus, relaxation modulus, and surface energy, as a method to predict performance related to the fatigue characteristics of asphalt binders by modeling intrinsic material flaws present amongst phase interfaces. It was revealed that oxidative aging induces substantial microstructural changes in asphalt, including variations in phase structure, phase properties, and phase distribution. It has also been shown that certain asphalt chemical parameters have a consistent and measureable effect on the asphalt microstructure that is observed with AFM. In fact, particular phases that emerged via chemical doping revealed a surprising correlation between oxidative aging and the saturates chemical parameter of asphalt in terms of how they explicitly impact durability and performance of asphalt. By implementing a crack initiation model – which requires measureable microstructural characteristics as an input parameter – it was found that microstructural flaws (depending on the extremity) can have a more profound impact on asphalt performance than the properties of the material located between the flaws. It was also discovered by comparing the findings to performance data in the Strategic Highway Research Program’s (SHRP’s) Materials Reference Library (MRL), that the crack initiation model predicts very similar performance as the SHRP’s distress resistance indicators. Overall, this body of work yields improved input values for asphalt prediction models and serves as the basis for ongoing studies in the areas of asphalt chemical mapping, modeling of nano-damage, and nano-modification using AFM.

The aim of this study was to determine the rheological properties of tahin/pekmez blends at different tahin concentrations (20-32%) and temperatures (35-65 &deg / C) by using a concentric cylinder rotational viscometer. Samples were sheared with seven different rotational speeds at an increasing order. The shear rates (0.75-63.9 s-1) were calculated by the Power-law Approximation method. Tahin/pekmez blends were found to exhibit non-Newtonian, shear thinning behavior at all temperatures and tahin concentrations. The experimental data of apparent viscosity versus shear rate were successfully described by the Power-law model. The model parameters / flow behavior index, n varied in the range of 0.7-0.85, whereas the values for the consistency coefficient, K, were in the range of 282-2547 mPa.sn. Apparent viscosity and consistency coefficient of blends increased with increasing tahin concentration and decreasing temperature. Temperature dependency of K was described by an Arrhenius-type equation. Activation energies (Ea) of the blends appeared in the range of 13376-28592 J/mol as the tahin concentration was increased from 20% to 32%. The effect of temperature on n was found to be significant but did not follow any descriptive trend. The relationship between K and tahin concentration was explained by exponential and power functions while tahin concentration had no significant effect on flow behavior index. Power function was found to be superior in explaining the variation of Ea with tahin concentration. A mathematical model was formulated to determine the combined effect of temperature, tahin concentration and shear rate on apparent viscosity.

Chicken dark meat has been considered as a major underutilized commodity due to the increasing demand for further processed breast meat products. Alkali aided protein extraction is an option to increase the utilization of chicken dark meat. First, the effect of pH (10.5-12.0) on alkaline extraction of chicken dark meat has been studied, and protein yield, composition, color, and TBARs of the extracted meat have been determined. Second, textural and rheological properties and water holding capacity (WHC) of alkali extracted chicken dark meat have been evaluated. The highest protein yield (94.2%) was obtained at pH 12.0. Lipid content of the extracted meat decreased by 50% compared to chicken dark meat. WHC, hardness and chewiness of extracted meat were greater at higher pH. The gel from recovered meat with added cryoprotectants showed more stability. This process may offer the possibility to use the underutilized poultry resources for preparation of functional foods. / Food Science and Technology

In this thesis, we investigate the structural and dynamical properties of nano-confined liquids by means of a new AFM-based technique that has the ability to measure normal force, lateral force, and the distance between the AFM tip and the sample simultaneously. Thanks to the mechanical stability of our apparatus, a judicious choice, and a new mechanical drift analysis, we are able to measure the tip-sample distance with sub-angstrom resolution, all the way down to the last liquid layer.

Samples collected from 5 bridge sites from around the state of Georgia are analyzed to determine their erosion and rheologic behavior. Most sites were subject to large amounts of local scour due to flood events resulting from Tropical Storm Alberto in 1994. According to the Federal Highway Administration's Hydraulic Engineering Circular No. 18 by Richardson and Davis (2001), scouring of bridge foundations is the most common cause of bridge failure resulting from floods. The erosion rates of the soils are measured in a rectangular tilting flume capable of applying up to 21 Pa of shear stress at the bed. Samples from Shelby tubes are extruded into the flow from below the bed using a hydraulic piston. The displacement is measured as a function of time using a cable-pull potentiometer. The soils are also subject to extensive geotechnical analysis. Sieve and hydrometer analyses are performed to obtain the particle size distribution for each sample. Atterberg Limits and other standard geotechnical measures are also found. Additionally, insight into the shear strength and cohesive nature of the fine (<0.75 micrometers) particles is gained using a stress controlled rheometer to measure the rheological characteristics of the slurry. These results are used to improve and extend a relationship for the critical shear stress of soils developed in previous research that can be used in bridge scour prediction formulae as affected by soil parameters. In addition, the rheologic properties of the soil in terms of a dimensionless yield stress are related to the critical value of the Shields parameter for estimating critical shear stress for erosion.

Wear of railroad rolling stock and rails costs millions of dollars annually in all rail systems throughout the world. The rail industry has attempted to address flange wear using rail curve lubricants and presently use a variety of lubricants and lubricant applicators. The choice of lubricant and applicator is currently based on considerations that do not address the wear problem directly. This research quantified rail curve lubricant performance through laboratory simulation. The effects of lubricants in the wheel/rail contact were investigated. Rail curve lubricant performance was measured with a laboratory rail/wheel simulator for the purpose of optimising the choice of lubricant. New methods for measurement of rail curve lubricant performance have been presented. These performance measurements are total absorbed energy, the energy absorbed in the lubricant film instead of being utilised for wear processes; total distance slid, the sliding distance or accumulated strain achieved prior to development of a set tractive force limit; half life of lubricant, the time taken for a lubricant to lose half of its sliding performance; and apparent viscosity, a measure of the lubricity presented with respect to accumulated strain. The rail/wheel simulator used in this research consists of two dissimilar wheels (disks) rotating in contact with one another simulating a conformal gauge corner contact. The first wheel, a simulated rail, is driven by an electric motor which then drives the second wheel, a simulated railroad wheel, through the contact. Hydraulic braking on the railroad wheel is used to simulate the rolling/sliding conditions. The variables of the simulated contact that are controlled with this equipment are normal force, input wheel speed, slip ratio between samples, sample geometries and material properties, and lubricant types. Rail curve lubricants were laboratory tested to define their properties using the ASTM and other appropriate standards. The performance differences measured using ASTM standards based tests were susceptible to repeatability problems and did not represent the contact as accurately as the rail/wheel simulator. This laboratory simulator was used to gather data in lubricated and unlubricated conditions for the purpose of providing lubricant performance measurements. These measurements were presented and the tested lubricants were ranked conclusively using three industrially relevant performance criteria. Total sliding distance and total absorbed energy measurements of the rail curve lubricants displayed clear differences in lubricant performance for both of these criteria. Total sliding distance is equivalent to the number of axles in the field situation, while total absorbed energy is the energy unavailable for wear processes of rails and wheels. Lubricants designed using these measurements will increase lubricant performance with respect to these performance criteria which in turn will reduce wear to both rails and wheels. Measurement of the apparent viscosity of rail curve lubricants, using the rail/wheel simulator, displayed changes in rheological characteristics with respect to accumulated strain. Apparent viscosity is a measure of the shear stress transmitted from the wheels to the rails. Designing a rail curve lubricant after analysing measurements taken from the rail/wheel simulator will assist in identifying lubricant properties to reduce the wear producing shear stresses generated in a rail wheel contact. Decay of lubricant performance was measured for three different rail curve lubricants under simulated conditions. The research found appreciable and quantifiable differences between lubricants. Industrial application of the findings will improve positioning of lubrication systems, improve choice of lubricants and predict effective lubrication distance from the lubricant application point. Using the new methods of lubricant performance measurement developed in this thesis, the objective of this research, to quantify rail curve lubricant performance through laboratory simulation, has been achieved.

The current study aims to investigate the relative contributions of each of the processes that govern airway smooth muscle mechanical behaviour. Studies have shown that breathing dynamics have a substantial effect on airway constriction in healthy and diseased subjects, yet little is known about the dynamic response of the main instigator of airway constriction, Airway Smooth Muscle (ASM). In this work several models are developed to further the understanding of ASM dynamics, particularly the roles and interactions of the three dominant processes in the muscle: contractile dynamics, length adaptation and passive dynamics. Three individual models have been developed, each describing a distinct process or structure within the muscle. The first is a contractile model which describes the contractile process and the influence of external excitation on contractile behaviour. The second model incorporates the contractile model to describe length adaptation, which includes the reorganisation and polymerisation of contractile elements in response to length changes. The third model describes the passive behaviour of the muscle, which entails the mechanical behaviour of all non-contractile components and processes. As little data on the passive dynamics of the muscle was available in the literature, a number of experiments were conducted to investigate relaxed ASM dynamics. The experimental data and mathematical modelling showed that passive dynamics plays not only a dominant role in relaxed ASM, but contributes considerably to the dynamics of contracted muscle as well. A novel theory of sequential multiplication in passive ASM is proposed and implemented in a mathematical model. Experiments and literature validated the model simulations. Further integration of the models and improved force control modelling of length adaptation is proposed for future study. It is likely that the coupling of the models presented here with models describing other airway wall components will provide a more complete picture of airway dynamics, which will be invaluable for understanding respiratory disease.

The current study aims to investigate the relative contributions of each of the processes that govern airway smooth muscle mechanical behaviour. Studies have shown that breathing dynamics have a substantial effect on airway constriction in healthy and diseased subjects, yet little is known about the dynamic response of the main instigator of airway constriction, Airway Smooth Muscle (ASM). In this work several models are developed to further the understanding of ASM dynamics, particularly the roles and interactions of the three dominant processes in the muscle: contractile dynamics, length adaptation and passive dynamics. Three individual models have been developed, each describing a distinct process or structure within the muscle. The first is a contractile model which describes the contractile process and the influence of external excitation on contractile behaviour. The second model incorporates the contractile model to describe length adaptation, which includes the reorganisation and polymerisation of contractile elements in response to length changes. The third model describes the passive behaviour of the muscle, which entails the mechanical behaviour of all non-contractile components and processes. As little data on the passive dynamics of the muscle was available in the literature, a number of experiments were conducted to investigate relaxed ASM dynamics. The experimental data and mathematical modelling showed that passive dynamics plays not only a dominant role in relaxed ASM, but contributes considerably to the dynamics of contracted muscle as well. A novel theory of sequential multiplication in passive ASM is proposed and implemented in a mathematical model. Experiments and literature validated the model simulations. Further integration of the models and improved force control modelling of length adaptation is proposed for future study. It is likely that the coupling of the models presented here with models describing other airway wall components will provide a more complete picture of airway dynamics, which will be invaluable for understanding respiratory disease.

Diss. (sammanfattning) Linköping : Univ., 2003. / Härtill 6 uppsatser.