Numerical studies of colloidal systems

The interplay of hydrodynamic and electrostatic forces is of great importance for the understanding of colloidal dispersions. Theoretical descriptions are often based on the so called standard electrokinetic model. This Mean Field approach combines the Stokes equation for the hydrodynamic flow field, the Poisson equation for electrostatics and a continuity equation describing the evolution of the ion concentration fields. In the first part of this thesis a new lattice method is presented in order to efficiently solve the set of non-linear equations for a charge-stabilized colloidal dispersion in the presence of an external electric field. Within this framework, the research is mainly focused on the calculation of the electrophoretic mobility. Since this transport coefficient is independent of the electric field only for small driving, the algorithm is based upon a linearization of the governing equations. The zeroth order is the well known Poisson-Boltzmann theory and the first order is a coupled set of linear equations. Furthermore, this set of equations is divided into several subproblems. A specialized solver for each subproblem is developed, and various tests and applications are discussed for every particular method. Finally, all solvers are combined in an iterative procedure and applied to several interesting questions, for example, the effect of the screening mechanism on the electrophoretic mobility or the charge dependence of the field-induced dipole moment and ion clouds surrounding a weakly charged sphere. In the second part a quantitative data analysis method is developed for a new experimental approach, known as "Total Internal Reflection Fluorescence Cross-Correlation Spectroscopy" (TIR-FCCS). The TIR-FCCS setup is an optical method using fluorescent colloidal particles to analyze the flow field close to a solid-fluid interface. The interpretation of the experimental results requires a theoretical model, which is usually the solution of a convection-diffusion equation. Since an analytic solution is not available due to the form of the flow field and the boundary conditions, an alternative numerical approach is presented. It is based on stochastic methods, i. e. a combination of a Brownian Dynamics algorithm and Monte Carlo techniques. Finally, experimental measurements for a hydrophilic surface are analyzed using this new numerical approach.

Total internal reflection fluorescence cross-correlation spectroscopy: theory and application for studying boundary slip phenomenon

I present a new experimental method called Total Internal Reflection Fluorescence Cross-Correlation Spectroscopy (TIR-FCCS). It is a method that can probe hydrodynamic flows near solid surfaces, on length scales of tens of nanometres. Fluorescent tracers flowing with the liquid are excited by evanescent light, produced by epi-illumination through the periphery of a high NA oil-immersion objective. Due to the fast decay of the evanescent wave, fluorescence only occurs for tracers in the ~100 nm proximity of the surface, thus resulting in very high normal resolution. The time-resolved fluorescence intensity signals from two laterally shifted (in flow direction) observation volumes, created by two confocal pinholes are independently measured and recorded. The cross-correlation of these signals provides important information for the tracers’ motion and thus their flow velocity. Due to the high sensitivity of the method, fluorescent species with different size, down to single dye molecules can be used as tracers. The aim of my work was to build an experimental setup for TIR-FCCS and use it to experimentally measure the shear rate and slip length of water flowing on hydrophilic and hydrophobic surfaces. However, in order to extract these parameters from the measured correlation curves a quantitative data analysis is needed. This is not straightforward task due to the complexity of the problem, which makes the derivation of analytical expressions for the correlation functions needed to fit the experimental data, impossible. Therefore in order to process and interpret the experimental results I also describe a new numerical method of data analysis of the acquired auto- and cross-correlation curves – Brownian Dynamics techniques are used to produce simulated auto- and cross-correlation functions and to fit the corresponding experimental data. I show how to combine detailed and fairly realistic theoretical modelling of the phenomena with accurate measurements of the correlation functions, in order to establish a fully quantitative method to retrieve the flow properties from the experiments. An importance-sampling Monte Carlo procedure is employed in order to fit the experiments. This provides the optimum parameter values together with their statistical error bars. The approach is well suited for both modern desktop PC machines and massively parallel computers. The latter allows making the data analysis within short computing times. I applied this method to study flow of aqueous electrolyte solution near smooth hydrophilic and hydrophobic surfaces. Generally on hydrophilic surface slip is not expected, while on hydrophobic surface some slippage may exists. Our results show that on both hydrophilic and moderately hydrophobic (contact angle ~85°) surfaces the slip length is ~10-15nm or lower, and within the limitations of the experiments and the model, indistinguishable from zero.

Formation of DNA complexes in aqueous and organic solvents

From a physical-chemical point of view, it is challenging to form complexes with polyelectrolytes, consisting of only molecule of the largest component, i.e. the component with the highest number of charges. In this study, complexes are formed with DNA because of its potential applications as an artificial vector for gene delivery. The aim of this work is to prepare complexes in aqueous solutions as well as in organic solvents containing only one DNA molecule. For this purpose, the topology, equilibrium and conformation of complexes between a supercoiled DNA pUC19 (2686 base pairs) and spermine containing hydrophilic and/or hydrophobic moieties or a polylysine with a hydrophilic block are determined by means of dynamic (DLS) and static light scattering (SLS), atomic force microscopy (AFM), and circular dichroism (CD) spectroscopy. It is demonstrated that all of these complexes consisted of only one molecule of the polyanion. Only the polylysine-b-polyethylene glycol copolymer satisfied the conditions: 1) 100% neutralization of DNA charges and with a small excess of the cation (lower than 30%) and 2) form stable complexes at every charge ratio. rnDNA complex formation is also investigated in organic solvents. Precipitation is induced by neutralizing the charge of the supercoiled DNA pUC19 with the surfactants dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB). After isolation and drying of the solids, the complexes are dissolved in organic solvents. DNA-TTA complexes are only soluble in methanol and DNA-DTA in DMF. The complexes again consisted of only one DNA molecule. The final topology of the complexes is different in methanol than in DMF. In the former case, DNA seems to be compacted whereas in the latter case, the DNA-DTA complexes seem to have an expanded conformation. Upon complex formation with polycations in organic solvents (with polyvilylpyridine brush (b-PVP) in methanol and with a protected polylysine in DMF), DNA aggregates and precipitates. rnDNA is linearized with an enzyme (SmaI) to investigate the influence of the initial topology of the polyanion on the final conformation of the complexes in organic solvents. Two main differences are evidenced: 1. Complexes in organic solvents formed with linear DNA have in general a more expanded conformation and a higher tendency to aggregate. 2. If a polycation, i.e. the b-PVP, is added to the linear DNA-TTA complexes in methanol, complexes with the polycation are formed at a higher charge ratio. In DMF, the addition of the same b-PVP and of b-PLL did not lead to the formation of complexes.rn

Computer simulations of colloidal fluids in confinement

Computer-Simulationen von Kolloidalen Fluiden in Beschränkten Geometrien Kolloidale Suspensionen, die einen Phasenübergang aufweisen, zeigen eine Vielfalt an interessanten Effekten, sobald sie auf eine bestimmte Geometrie beschränkt werden, wie zum Beispiel auf zylindrische Poren, sphärische Hohlräume oder auf einen Spalt mit ebenen Wänden. Der Einfluss dieser verschiedenen Geometrietypen sowohl auf das Phasenverhalten als auch auf die Dynamik von Kolloid-Polymer-Mischungen wird mit Hilfe von Computer-Simulationen unter Verwendung des Asakura-Oosawa- Modells, für welches auf Grund der “Depletion”-Kräfte ein Phasenübergang existiert, untersucht. Im Fall von zylindrischen Poren sieht man ein interessantes Phasenverhalten, welches vom eindimensionalen Charakter des Systems hervorgerufen wird. In einer kurzen Pore findet man im Bereich des Phasendiagramms, in dem das System typischerweise entmischt, entweder eine polymerreiche oder eine kolloidreiche Phase vor. Sobald aber die Länge der zylindrischen Pore die typische Korrelationslänge entlang der Zylinderachse überschreitet, bilden sich mehrere quasi-eindimensionale Bereiche der polymerreichen und der kolloidreichen Phase, welche von nun an koexistieren. Diese Untersuchungen helfen das Verhalten von Adsorptionshysteresekurven in entsprechenden Experimenten zu erklären. Wenn das Kolloid-Polymer-Modellsystem auf einen sphärischen Hohlraum eingeschränkt wird, verschiebt sich der Punkt des Phasenübergangs von der polymerreichen zur kolloidreichen Phase. Es wird gezeigt, dass diese Verschiebung direkt von den Benetzungseigenschaften des Systems abhängt, was die Beobachtung von zwei verschiedenen Morphologien bei Phasenkoexistenz ermöglicht – Schalenstrukturen und Strukturen des Janustyps. Im Rahmen der Untersuchung von heterogener Keimbildung von Kristallen innerhalb einer Flüssigkeit wird eine neue Simulationsmethode zur Berechnung von Freien Energien der Grenzfläche zwischen Kristall- bzw. Flüssigkeitsphase undWand präsentiert. Die Resultate für ein System von harten Kugeln und ein System einer Kolloid- Polymer-Mischung werden anschließend zur Bestimmung von Kontaktwinkeln von Kristallkeimen an Wänden verwendet. Die Dynamik der Phasenseparation eines quasi-zweidimensionalen Systems, welche sich nach einem Quench des Systems aus dem homogenen Zustand in den entmischten Zustand ausbildet, wird mit Hilfe von einer mesoskaligen Simulationsmethode (“Multi Particle Collision Dynamics”) untersucht, die sich für eine detaillierte Untersuchung des Einflusses der hydrodynamischen Wechselwirkung eignet. Die Exponenten universeller Potenzgesetze, die das Wachstum der mittleren Domänengröße beschreiben, welche für rein zwei- bzw. dreidimensionale Systeme bekannt sind, können für bestimmte Parameterbereiche nachgewiesen werden. Die unterschiedliche Dynamik senkrecht bzw. parallel zu den Wänden sowie der Einfluss der Randbedingungen für das Lösungsmittel werden untersucht. Es wird gezeigt, dass die daraus resultierende Abschirmung der hydrodynamischen Wechselwirkungsreichweite starke Auswirkungen auf das Wachstum der mittleren Domänengröße hat.

Tracer diffusion at water-oil interfaces studied by fluorescence correlation spectroscopy

The adsorption of particles and surfactants at water-oil interfaces has attracted continuous attention because of its emulsion stabilizing effect and the possibility to form two-dimensional materials. Herein, I studied the interfacial diffusion of single molecules and nanoparticles at water-oil interfaces using fluorescence correlation spectroscopy. rnrnFluorescence correlation spectroscopy (FCS) is a promising technique to study diffusion of fluorescent tracers in diverse conditions. This technique monitors and analyzes the fluorescence fluctuation caused by single fluorescent tracers coming in and out of a diffraction-limited observation volume “one at a time”. Thus, this technique allows a combination of high precision, high spatial resolution and low tracer concentration. rnrnIn chapter 1, I discussed some controversial questions regarding the properties of water-hydrophobic interfaces and also introduced the current progress on the stability and dynamic of single nanoparticles at water-oil interfaces. The materials and setups I used in this thesis were summarized in chapter 2. rnrnIn chapter 3, I presented a new strategy to study the properties of water-oil interfaces. The two-dimensional diffusion of isolated molecular tracers at water/n-alkane interfaces was measured using fluorescence correlation spectroscopy. The diffusion coefficients of larger tracers with a hydrodynamic radius of 4.0 nm agreed well with the values calculated from the macroscopic viscosities of the two bulk phases. However, for small molecule tracers with hydrodynamic radii of only 1.0 and 0.6 nm, notable deviations were observed, indicating the existence of an interfacial region with a reduced effective viscosity. rnrnIn chapter 4, the interfacial diffusion of nanoparticles at water-oil interfaces was investigated using FCS. In stark contrast to the interfacial diffusion of molecular tracers, that of nanoparticles at any conditions is slower than the values calculated in accordance to the surrounding viscosity. The diffusion of nanoparticles at water-oil interfaces depended on the interfacial tension of liquid-liquid interfaces, the surface properties of nanoparticles, the particle sizes and the viscosities of surrounding liquid phases. In addition, the interfacial diffusion of nanoparticles with Janus motif is even slower than that of their symmetric counterparts. Based on the experimental results I obtained, I drew some possibilities to describe the origin of nanoparticle slowdown at water-oil interfaces.

Dynamic wetting of complex liquids

A simple dependency between contact angle θ and velocity or surface tension has been predicted for the wetting and dewetting behavior of simple liquids. According to the hydrodynamic theory, this dependency was described by Cox and Voinov as θ ∼ Ca^(1/3) (Ca: Capillary number). For more complex liquids like surfactant solutions, this prediction is not directly given.rnHere I present a rotating drum setup for studying wetting/dewetting processes of surfactant solutions on the basis of velocity-dependent contact angle measurements. With this new setup I showed that surfactant solutions do not follow the predicted Cox-Voinov relation, but showed a stronger contact angle dependency on surface tension. All surfactants independent of their charge showed this difference from the prediction so that electrostatic interactions as a reason could be excluded. Instead, I propose the formation of a surface tension gradient close to the three-phase contact line as the main reason for the strong contact angle decrease with increasing surfactant concentration. Surface tension gradients are not only formed locally close to the three-phase contact line, but also globally along the air-liquid interface due to the continuous creation/destruction of the interface by the drum moving out of/into the liquid. By systematically hindering the equilibration routes of the global gradient along the interface and/or through the bulk, I was able to show that the setup geometry is also important for the wetting/dewetting of surfactant solutions. Further, surface properties like roughness or chemical homogeneity of the wetted/dewetted substrate influence the wetting/dewetting behavior of the liquid, i. e. the three-phase contact line is differently pinned on rough/smooth or homogeneous/inhomogeneous surfaces. Altogether I showed that the wetting/dewetting of surfactant solutions did not depend on the surfactant type (anionic, cationic, or non-ionic) but on the surfactant concentration and strength, the setup geometry, and the surface properties.rnSurfactants do not only influence the wetting/dewetting behavior of liquids, but also the impact behavior of drops on free-standing films or solutions. In a further part of this work, I dealt with the stability of the air cushion between drop and film/solution. To allow coalescence between drop and substrate, the air cushion has to vanish. In the presence of surfactants, the vanishing of the air is slowed down due to a change in the boundary condition from slip to no-slip, i. e. coalescence is suppressed or slowed down in the presence of surfactant.

Wet bioadhesion in tree frogs

Viele Tiere wie etwa Geckos oder Laubfrösche können mittels ihrer Haftscheiben an Oberflächen kleben. Diese Haftscheiben ermöglichen es den Tieren, sich während ihrerrnFortbewegung an Oberflächen anzuheften und wieder zu lösen unabhängig von denrnvorherrschenden Umweltbedingungen. Frösche besitzen mikro- und nanostrukturierternsowie charakteristisch geformte Haftscheiben an Finger- und Zehenenden. Ihre besonderernevolutionäre Errungenschaft, sich stark und zugleich reversibel in sowohl trockenen alsrnauch feuchten Umgebungen anzuhaften, hat die Wissenschaft zur Nachahmung und Untersuchungrndieser Strukturen inspiriert. Zum besseren Verständnis der Mechanismen vonrnAnhaftung und Loslösung bei Laubfröschen wurden weiche, elastische und mikrostrukturierternOberflächen hergestellt, indem PDMS (Polydimethylsiloxan) auf einer Siliziummaskernmit Hexagonstruktur aufgetragen und vernetzt wurde. Dadurch wurden Anordnungenrnvon hexagonalen Mikrosäulen mit spezifischen geometrischen Eigenschaften undrnunterschiedlichen Kontaktgeometrien (normale, flache Form, T-Form und konkave Formrnder Säulenenden) erhalten. Um den Einfluss der van-der-Waals, hydrodynamischen,rnKapillar-und Adhäsionskräfte zu verstehen, wurden verschiedene experimentelle Ansätzernverfolgt: Die auf eine einzelne Säule wirkenden Adhäsionskräfte wurden mittelsrnRasterkraftmikroskopie gemessen. Dazu wurden speziell hergestellte kolloidale Sensorenrnverwendet. Diese Experimente wurden sowohl mit als auch ohne Flüssigkeitsfilm auf derrnSäule durchgeführt. Die Ergebnisse zeigten den Beitrag von Kapillarkraft und direktenrnKontaktkräften zur Adhäsionskraft bei Vorliegen eines Flüssigkeitsfilms. Die Adhäsionrnfiel umso größer aus, je weniger Flüssigkeit zwischen Sensor und Säule vorhanden war.rnIm Falle einer trockenen Adhäsion zeigte die Säule mit T-Form die höchste Adhäsion. Darndie Haftscheiben der Laubfrösche weich sind, können sie dynamisch ihre Form ändern,rnwas zu einer Änderung der hydrodynamischen Kraft zwischen Scheibe und Oberflächernführt. Der Einfluss der Oberflächenverformbarkeit auf die hydrodynamische Kraft wurderndaher am Modellsystem einer Kugel untersucht, welche sich einer weichen und ebenenrnOberfläche annähert. Dieses System wurde sowohl theoretisch über die Simulation finiterrnElemente als auch experimentell über die Messung mit kolloidalen Sonden untersucht.rnSowohl experimentelle Ergebnisse als auch die Simulationen ergaben eine Abnahme derrnhydrodynamischen Kraft bei Annäherung des kolloidalen Sensors an eine weiche undrnelastische Oberfläche. Beim Entfernen der Sensors von der Oberfläche verstärkte sichrndie hydrodynamische Anziehungskraft. Die Kraft, die zur Trennung eines Partikels von einer Oberfläche in Flüssigkeit notwendig ist, ist für weiche und elastischen Oberflächenrngrößer als für harte Oberflächen. In Bezug zur Bioadhäsion bei Laubfröschen konnternfestgestellt somit festgestellt werden, dass sich der hydrodynamische Anteil zur feuchtenrnBioadhäsion aufgrund der weichen Oberfläche erhöht. Weiterhin wurde der Einflussrndes Aspektverhältnisses der Säulen auf die Reibungskraft mittels eines kolloidalen Sensorsrnuntersucht. Gestreckte Säulen zeigten dabei eine höhere Reibung im Vergleich zu.rnSäulen mit einem gestreckten Hexagon als Querschnitt.

Plasmonic nanoparticles as sensors : a novel approach to quantify adsorption and diffusion kinetics

Biosensors find wide application in clinical diagnostics, bioprocess control and environmental monitoring. They should not only show high specificity and reproducibility but also a high sensitivity and stability of the signal. Therefore, I introduce a novel sensor technology based on plasmonic nanoparticles which overcomes both of these limitations. Plasmonic nanoparticles exhibit strong absorption and scattering in the visible and near-infrared spectral range. The plasmon resonance, the collective coherent oscillation mode of the conduction band electrons against the positively charged ionic lattice, is sensitive to the local environment of the particle. I monitor these changes in the resonance wavelength by a new dark-field spectroscopy technique. Due to a strong light source and a highly sensitive detector a temporal resolution in the microsecond regime is possible in combination with a high spectral stability. This opens a window to investigate dynamics on the molecular level and to gain knowledge about fundamental biological processes.rnFirst, I investigate adsorption at the non-equilibrium as well as at the equilibrium state. I show the temporal evolution of single adsorption events of fibrinogen on the surface of the sensor on a millisecond timescale. Fibrinogen is a blood plasma protein with a unique shape that plays a central role in blood coagulation and is always involved in cell-biomaterial interactions. Further, I monitor equilibrium coverage fluctuations of sodium dodecyl sulfate and demonstrate a new approach to quantify the characteristic rate constants which is independent of mass transfer interference and long term drifts of the measured signal. This method has been investigated theoretically by Monte-Carlo simulations but so far there has been no sensor technology with a sufficient signal-to-noise ratio.rnSecond, I apply plasmonic nanoparticles as sensors for the determination of diffusion coefficients. Thereby, the sensing volume of a single, immobilized nanorod is used as detection volume. When a diffusing particle enters the detection volume a shift in the resonance wavelength is introduced. As no labeling of the analyte is necessary the hydrodynamic radius and thus the diffusion properties are not altered and can be studied in their natural form. In comparison to the conventional Fluorescence Correlation Spectroscopy technique a volume reduction by a factor of 5000-10000 is reached.

Magnetische Multischalenpartikel für den Transport von siRNA

Die vorliegende Arbeit befasst sich mit der Entwicklung eines nichtviralen, effizienten Transfektionsmittels mit einer Kern-Schale-Struktur in der Größenordnung bis 100 nm. Dafür werden magnetische, negativ geladene Eisenoxid-Nanopartikel mittels Thermolyse mit einem Durchmesser von 17 nm synthetisiert und in Wasser überführt. Diese Nanopartikel bilden den Kern des Erbgut-Trägers und werden mittels Layer-by-Layer –Verfahren (LbL) mit geladenen Polymeren, den bioabbaubaren Makromolekülen Poly-L-Lysin und Heparin, beschichtet. Dafür wird zunächst eine geeignete Apparatur aufgebaut. Diese wird zur Herstellung von Kern-Schale-Strukturen mit fünf Polyelektrolytschichten verwendet und liefert Partikel mit einem hydrodynamischen Durchmesser von 58 nm, die bei Abwesenheit von niedermolekularem Salz aggregatfrei sind. Das System wird gegen Salz stabilisiert, indem die letzte Poly-L-Lysin-Schicht mit Polyethylenglycol modifiziert wird. Die so entstandenen Multischalenpartikel zeigen weder im PBS-Puffer noch in humanem Serum Aggregation. Mittels winkelabhängiger dynamischer Lichtstreuung wird die Aggregatbildung kontrolliert, während ζ-Potential-Messungen die Kontrolle der Oberflächenladung erlauben.rnDa siRNA auf Grund ihres negativ geladenen Phosphat-Rückgrats ebenfalls ein Polyelektrolyt ist, wird sie aggregatfrei auf die positiv geladenen PLL-Nanopartikel aufgetragen. Die eingesetzte siRNA ist farbstoffmarkiert, um eine Detektion in vitro zu ermöglichen. Jedoch sind die entstandenen Komplexe mittels Fluoreszenzkorrelations-spektroskopie (FCS) nicht nachweisbar. Auch die Fluoreszenzmarkierung der PEGylierten Außenschale mittels kupferfreier Click-Chemie ist in der FCS nicht sichtbar, sodass eine Fluoreszenzauslöschung der Farbstoffe in den Multischalenpartikeln vermutet wird.rn

Hydrodynamics and solid dosage form disintegration/dissolution : immediate release tablets and novel in situ polyelectrolyte gastroretentive drug delivery systems

Solid oral dosage form disintegration in the human stomach is a highly complex process dependent on physicochemical properties of the stomach contents as well as on physical variables such as hydrodynamics and mechanical stress. Understanding the role of hydrodynamics and forces in disintegration of oral solid dosage forms can help to improve in vitro disintegration testing and the predictive power of the in vitro test. The aim of this work was to obtain a deep understanding of the influence of changing hydrodynamic conditions on solid oral dosage form performance. Therefore, the hydrodynamic conditions and forces present in the compendial PhEur/USP disintegration test device were characterized using a computational fluid dynamics (CFD) approach. Furthermore, a modified device was developed and the hydrodynamic conditions present were simulated using CFD. This modified device was applied in two case studies comprising immediate release (IR) tablets and gastroretentive drug delivery systems (GRDDS). Due to the description of movement provided in the PhEur, the movement velocity of the basket-rack assembly follows a sinusoidal profile. Therefore, hydrodynamic conditions are changing continually throughout the movement cycle. CFD simulations revealed that the dosage form is exposed to a wide range of fluid velocities and shear forces during the test. The hydrodynamic conditions in the compendial device are highly variable and cannot be controlled. A new, modified disintegration test device based on computerized numerical control (CNC) technique was developed. The modified device can be moved in all three dimensions and radial movement is also possible. Simple and complex moving profiles can be developed and the influence of the hydrodynamic conditions on oral solid dosage form performance can be evaluated. Furthermore, a modified basket was designed that allows two-sided fluid flow. CFD simulations of the hydrodynamics and forces in the modified device revealed significant differences in the fluid flow field and forces when compared to the compendial device. Due to the CNC technique moving velocity and direction are arbitrary and hydrodynamics become controllable. The modified disintegration test device was utilized to examine the influence of moving velocity on disintegration times of IR tablets. Insights into the influence of moving speed, medium viscosity and basket design on disintegration times were obtained. An exponential relationship between moving velocity of the modified basket and disintegration times was established in simulated gastric fluid. The same relationship was found between the disintegration times and the CFD predicted average shear stress on the tablet surface. Furthermore, a GRDDS was developed based on the approach of an in situ polyelectrolyte complex (PEC). Different complexes composed of different grades of chitosan and carrageenan and different ratios of those were investigated for their swelling behavior, mechanical stability, and in vitro drug release. With an optimized formulation the influence of changing hydrodynamic conditions on the swelling behavior and the drug release profile was demonstrated using the modified disintegration test device. Both, swelling behavior and drug release, were largely dependent on the hydrodynamic conditions. Concluding, it has been shown within this thesis that the application of the modified disintegration test device allows for detailed insights into the influence of hydrodynamic conditions on solid oral dosage form disintegration and dissolution. By the application of appropriate test conditions, the predictive power of in vitro disintegration testing can be improved using the modified disintegration test device. Furthermore, CFD has proven a powerful tool to examine the hydrodynamics and forces in the compendial as well as in the modified disintegration test device. rn

Hydraulic evaluation of the gyro electric wave energy converter

Motivation Thanks for a scholarship offered by ALma Mater Studiorum I could stay in Denmark for six months during which I could do physical tests on the device Gyro PTO at the Departmet of Civil Engineering of Aalborg University. Aim The goal of my thesis is an hydraulic evaluation of the device: Gyro PTO, a gyroscopic device for conversion of mechanical energy in ocean surface waves to electrical energy. The principle of the system is the application of the gyroscopic moment of flywheels equipped on a swing float excited by waves. The laboratory activities were carried out by: Morten Kramer, Jan Olsen, Irene Guaraldi, Morten Thøtt, Nikolaj Holk. The main purpose of the tests was to investigate the power absorption performance in irregular waves, but testing also included performance measures in regular waves and simple tests to get knowledge about characteristics of the device, which could facilitate the possibility of performing numerical simulations and optimizations. Methodology To generate the waves and measure the performance of the device a workstation was created in the laboratory. The workstation consist of four computers in each of wich there was a different program. Programs have been used : Awasys6, LabView, Wave lab, Motive optitrack, Matlab, Autocad Main Results Thanks to the obtained data with the tank testing was possible to make the process of wave analisys. We obtained significant wave height and period through a script Matlab and then the values of power produced, and energy efficiency of the device for two types of waves: regular and irregular. We also got results as: physical size, weight, inertia moments, hydrostatics, eigen periods, mooring stiffness, friction, hydrodynamic coefficients etc. We obtained significant parameters related to the prototype in the laboratory after which we scale up the results obtained for two future applications: one in Nissun Brending and in the North Sea. Conclusions The main conclusion on the testing is that more focus should be put into ensuring a stable and positive power output in a variety of wave conditions. In the irregular waves the power production was negative and therefore it does not make sense to scale up the results directly. The average measured capture width in the regular waves was 0.21 m. As the device width is 0.63 m this corresponds to a capture width ratio of: 0.21/0.63 * 100 = 33 %. Let’s assume that it is possible to get the device to produce as well in irregular waves under any wave conditions, and lets further assume that the yearly absorbed energy can be converted into electricity at a PTO-efficiency of 90 %. Under all those assumptions the results in table are found, i.e. a Nissum Bredning would produce 0.87 MWh/year and a North Sea device 85 MWh/year.

Analisi idrogeologica dell'area carsica dei Monti Alburni (Salerno, Campania)

The Alburni Massif is the most important karstic area in southern Italy and It contains about 250 caves. Most of these caves are located on the plateau, between 1500 m a.s.l. and 700 m a.s.l., and only a few reach the underground streams that feed the springs and the deep aquifer. The main springs are Grotta di Pertosa-Auletta (CP1) and Auso spring (CP31), both located at 280 m a.s.l., the first on the south-eastern margin whereas the second on south-west margin, and the springs present in Castelcivita area, the Castelcivita-Ausino system (CP2) and Mulino di Castelcivita spring (CP865), located at 60 m a.s.l.. Some other secondary springs are present too. We have monitored Pertosa-Auletta’s spring with a multiparameter logger. This logger has registered data from November 2014 to December 2015 regarding water level, electric conductivity and temperature. The hydrodynamic monitoring has been supported by a sampling campaign in order to obtain chemical water analyses. The work was done from August 2014 to December 2015, not only at Pertosa but also at all the other main springs, and in some caves. It was possible to clarify the behavior of Pertosa-Auletta’s spring, almost exclusively fed by full charge conduits, only marginally affected by seasonal rains. Pertosa-Auletta showed a characteristic Mg/Ca ratio and Mg2+ enrichment, as demonstrated by its saturation index that always showed a dolomite saturation. All other spring have characteristic waters from a chemical point of view. In particular, it highlights the great balance between the components dissolved in the waters of Mulino’ spring opposed to the variability of the nearby Castelcivita-Ausino spring. Regarding the Auso spring the variable behavior in terms of discharge and chemistry is confirmed, greatly influenced by rainfall and, during drought periods, by full charge conduits. Rare element concentrations were also analyzed and allowed to characterize further the different waters. Based on all these data an updated hydrogeological map of the Alburni massif has been drawn, that defines in greater detail the hydrogeological complexes on the basis of lithologies, and therefore of their chemical characteristics.

Dynamic computer simulations of electrophoresis: a versatile research and teaching tool

Software is available, which simulates all basic electrophoretic systems, including moving boundary electrophoresis, zone electrophoresis, ITP, IEF and EKC, and their combinations under almost exactly the same conditions used in the laboratory. These dynamic models are based upon equations derived from the transport concepts such as electromigration, diffusion, electroosmosis and imposed hydrodynamic buffer flow that are applied to user-specified initial distributions of analytes and electrolytes. They are able to predict the evolution of electrolyte systems together with associated properties such as pH and conductivity profiles and are as such the most versatile tool to explore the fundamentals of electrokinetic separations and analyses. In addition to revealing the detailed mechanisms of fundamental phenomena that occur in electrophoretic separations, dynamic simulations are useful for educational purposes. This review includes a list of current high-resolution simulators, information on how a simulation is performed, simulation examples for zone electrophoresis, ITP, IEF and EKC and a comprehensive discussion of the applications and achievements.

Added mass and wave radiation damping for flow-induced rotational vibrations of skinplates of hydraulic gates

One observed vibration mode for Tainter gate skinplates involves the bending of the skinplate about a horizontal nodal line. This vibration mode can be approximated as a streamwise rotational vibration about the horizontal nodal line. Such a streamwise rotational vibration of a Tainter gate skinplate must push away water from the portion of the skinplate rotating into the reservoir and draw water toward the gate over that portion of the skinplate receding from the reservoir. The induced pressure is termed the push-and-draw pressure. In the present paper, this push-and-draw pressure is analyzed using the potential theory developed for dissipative wave radiation problems. In the initial analysis, the usual circular-arc skinplate is replaced by a vertical, flat, rigid weir plate so that theoretical calculations can be undertaken. The theoretical push-and-draw pressure is used in the derivation of the non-dimensional equation of motion of the flow-induced rotational vibrations. Non-dimensionalization of the equation of motion permits the identification of the dimensionless equivalent added mass and the wave radiation damping coefficients. Free vibration tests of a vertical, flat, rigid weir plate model, both in air and in water, were performed to measure the equivalent added mass and the wave radiation damping coefficients. Experimental results compared favorably with the theoretical predictions, thus validating the theoretical analysis of the equivalent added mass and wave radiation damping coefficients as a prediction tool for flow-induced vibrations. Subsequently, the equation of motion of an inclined circular-arc skinplate was developed by incorporating a pressure correction coefficient, which permits empirical adaptation of the results from the hydrodynamic pressure analysis of the vertical, flat, rigid weir plate. Results from in-water free vibration tests on a 1/31-scale skinplate model of the Folsom Dam Tainter gate are used to demonstrate the utility of the equivalent added mass coefficient.

Biomechanics on the Half Shell: Functional Performance Influences Patterns of Morphological Variation in the Emydid Turtle carapace

This study uses the carapace of emydid turtles to address hypothesized differences between terrestrial and aquatic species. Geometric morphometrics are used to quantify shell shape, and performance is estimated for two shell functions: shell strength and hydrodynamics. Aquatic turtle shells differ in shape from terrestrial turtle shells and are characterized by lower frontal areas and presumably lower drag. Terrestrial turtle shells are stronger than those of aquatic turtles; many-to-one mapping of morphology to function does not entirely mitigate a functional trade-off between mechanical strength and hydrodynamic performance. Furthermore, areas of morphospace characterized by exceptionally poor performance in either of the functions are not occupied by any emydid species. Though aquatic and terrestrial species show no significant differences in the rate of morphological evolution, aquatic species show a higher lineage density, indicative of a greater amount of convergence in their evolutionary history. The techniques employed in this study, including the modeling of theoretical shapes to assess performance in unoccupied areas of morphospace, suggest a framework for future studies of morphological variation.