Meccanismi di formazione dei tubi di lava

Two analytical models are proposed to describe two different mechanisms of lava tubes formation. A first model is introduced to describe the development of a solid crust in the central region of the channel, and the formation of a tube when crust widens until it reaches the leve\'es. The Newtonian assumption is considered and the steady state Navier- Stokes equation in a rectangular conduit is solved. A constant heat flux density assigned at the upper flow surface resumes the combined effects of two thermal processes: radiation and convection into the atmosphere. Advective terms are also included, by the introduction of velocity into the expression of temperature. Velocity is calculated as an average value over the channel width, so that lateral variations of temperature are neglected. As long as the upper flow surface cools, a solid layer develops, described as a plastic body, having a resistance to shear deformation. If the applied shear stress exceeds this resistance, crust breaks, otherwise, solid fragments present at the flow surface can weld together forming a continuous roof, as it happens in the sidewall flow regions. Variations of channel width, ground slope and effusion rate are analyzed, as parameters that strongly affect the shear stress values. Crust growing is favored when the channel widens, and tube formation is possible when the ground slope or the effusion rate reduce. A comparison of results is successfully made with data obtained from the analysis of pictures of actual flows. The second model describes the formation of a stable, well defined crust along both channel sides, their growing towards the center and their welding to form the tube roof. The fluid motion is described as in the model above. Thermal budget takes into account conduction into the atmosphere, and advection is included considering the velocity depending both on depth and channel width. The solidified crust has a non uniform thickness along the channel width. Stresses acting on the crust are calculated using the equations of the elastic thin plate, pinned at its ends. The model allows to calculate the distance where crust thickness is able to resist the drag of the underlying fluid and to sustain its weight by itself, and the level of the fluid can lower below the tube roof. Viscosity and thermal conductivity have been experimentally investigated through the use of a rotational viscosimeter. Analyzing samples coming from Mount Etna (2002) the following results have been obtained: the fluid is Newtonian and the thermal conductivity is constant in a range of temperature above the liquidus. For lower temperature, the fluid becomes non homogeneous, and the used experimental techniques are not able to detect any properties, because measurements are not reproducible.

Sistemi liquido cristallini complessi: simulazioni al calcolatore e studi ESR

The aim of this PhD thesis was to study at a microscopic level different liquid crystal (LC) systems, in order to determine their physical properties, resorting to two distinct methodologies, one involving computer simulations, and the other spectroscopic techniques, in particular electron spin resonance (ESR) spectroscopy. By means of the computer simulation approach we tried to demonstrate this tool effectiveness for calculating anisotropic static properties of a LC material, as well as for predicting its behaviour and features. This required the development and adoption of suitable molecular models based on a convenient intermolecular potentials reflecting the essential molecular features of the investigated system. In particular, concerning the simulation approach, we have set up models for discotic liquid crystal dimers and we have studied, by means of Monte Carlo simulations, their phase behaviour and self­-assembling properties, with respect to the simple monomer case. Each discotic dimer is described by two oblate Gay­Berne ellipsoids connected by a flexible spacer, modelled by a harmonic "spring" of three different lengths. In particular we investigated the effects of dimerization on the transition temperatures, as well as on the characteristics of molecular aggregation displayed and the relative orientational order. Moving to the experimental results, among the many experimental techniques that are typically employed to evaluate LC system distinctive features, ESR has proved to be a powerful tool in microscopic scale investigation of the properties, structure, order and dynamics of these materials. We have taken advantage of the high sensitivity of the ESR spin probe technique to investigate increasingly complex LC systems ranging from devices constituted by a polymer matrix in which LC molecules are confined in shape of nano- droplets, as well as biaxial liquid crystalline elastomers, and dimers whose monomeric units or lateral groups are constituted by rod-like mesogens (11BCB). Reflection-mode holographic-polymer dispersed liquid crystals (H-PDLCs) are devices in which LCs are confined into nanosized (50­-300 nm) droplets, arranged in layers which alternate with polymer layers, forming a diffraction grating. We have determined the configuration of the LC local director and we have derived a model of the nanodroplet organization inside the layers. Resorting also to additional information on the nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross-section, the observed director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi- monodomain aligned along the nanodroplet long axis. The results suggest that the molecular organization is dictated mainly by the confinement, explaining, at least in part, the need for switching voltages significantly higher and the observed faster turn-off times in H-PDLCs compared to standard PDLC devices. Liquid crystal elastomers consist in cross-linked polymers, in which mesogens represent the monomers constituting the main chain or the laterally attached side groups. They bring together three important aspects: orientational order in amorphous soft materials, responsive molecular shape and quenched topological constraints. In biaxial nematic liquid crystalline elastomers (BLCEs), two orthogonal directions, rather than the one of normal uniaxial nematic, can be controlled, greatly enhancing their potential value for applications as novel actuators. Two versions of a side-chain BLCEs were characterized: side­-on and end­-on. Many tests have been carried out on both types of LCE, the main features detected being the lack of a significant dynamical behaviour, together with a strong permanent alignment along the principal director, and the confirmation of the transition temperatures already determined by DSC measurements. The end­-on sample demonstrates a less hindered rotation of the side group mesogenic units and a greater freedom of alignment to the magnetic field, as already shown by previous NMR studies. Biaxial nematic ESR static spectra were also obtained on the basis of Molecular Dynamics generated biaxial configurations, to be compared to the experimentally determined ones, as a mean to establish a possible relation between biaxiality and the spectral features. This provides a concrete example of the advantages of combining the computer simulation and spectroscopic approaches. Finally, the dimer α,ω-bis(4'-cyanobiphenyl-4-yl)undecane (11BCB), synthesized in the "quest" for the biaxial nematic phase has been analysed. Its importance lies in the dimer significance as building blocks in the development of new materials to be employed in innovative technological applications, such as faster switching displays, resorting to the easier aligning ability of the secondary director in biaxial phases. A preliminary series of tests were performed revealing the population of mesogenic molecules as divided into two groups: one of elongated straightened conformers sharing a common director, and one of bent molecules, which display no order, being equally distributed in the three dimensions. Employing this model, the calculated values show a consistent trend, confirming at the same time the transition temperatures indicated by the DSC measurements, together with rotational diffusion tensor values that follow closely those of the constituting monomer 5CB.

Quantenkorrekturen an magnetischen Domänenwänden auf Gitterstrukturen

Wir betrachten die eindimensionale Heisenberg-Spinkette aus einem neuen und aktuelleren Blickwinkel. Experimentelle Techniken der Herstellung und selbstverständlich auch experimentelle Meßmethoden erlauben nicht nur die Herstellung von Nanopartikeln und Nanodrähten, sondern gestatten es auch, Domänenwände in diesen Strukturen auszumessen. Die meisten heute verwendeten Theorien und Simulationsmethoden haben ihre Grundlage im mikromagnetischen Kontinuumsmodell, daß schon über Jahrzehnte hinweg erforscht und erprobt ist. Wir stellen uns jedoch die Frage, ob die innere diskrete Struktur der Substrate und die quantenmechanischen Effekte bei der Genauigkeit heutiger Messungen in Betracht gezogen werden müssen. Dazu wählen wir einen anderen Ansatz. Wir werden zunächst den wohlbekannten klassischen Fall erweitern, indem wir die diskrete Struktur der Materie in unseren Berechnungen berücksichtigen. Man findet in diesem Formalismus einen strukturellen Phasenübergang zwischen einer Ising-artigen und einer ausgedehnten Wand. Das führt zu bestimmten Korrekturen im Vergleich zum Kontinuumsfall. Der Hauptteil dieser Arbeit wird sich dann mit dem quantenmechanischen Fall beschäftigen. Wir rotieren das System zunächst mit einer Reihe lokaler Transformationen derart, daß alle Spins in die z-Richtung ausgerichtet sind. Im Rahmen einer 1/S-Entwicklung läßt sich der erhaltene neue Hamilton-Operator diagonalisieren. Setzt man hier die klassische Lösung ein, so erhält man Anregungsmoden in diesem Grenzfall. Unsere Resultate erweitern und bestätigen frühere Berechnungen. Mit Hilfe der Numerik wird schließlich der Erwartungswert der Energie minimiert und somit die Form der Domänenwand im quantenmechanischen Fall berechnet. Hieraus ergeben sich auch bestimmte Korrekturen zum kritischen Verhalten des Systems. Diese Ergebnisse sind vollkommen neu.

Grating coupled surface plasmon enhanced fluorescence spectroscopy

Over the last three decades, sensors based on the phenomenon of surface plasmon resonance have proven particularly suitable for real time thin film characterization, gas detection, biomolecular interaction examination and to supplement electrochemical methods. Systems based on prism coupling have been combined with fluorescence detection under the name of surface plasmon fluorescence spectroscopy to increase sensitivity even further. Alternatively, metal gratings can be employed to match photons for plasmon resonance. The real time monitoring of binding reactions not yet been reported in the combination of fluorescence detection and grating coupling. Grating-based systems promise more competitive products, because of reduced operating costs, and offer benefits for device engineering. This thesis is comprised of a comprehensive study of the suitability of grating coupling for fluorescence based analyte detection. Fundamental properties of grating coupled surface plasmon fluorescence spectroscopy are described, as well as issues related to the commercial realization of the method. Several new experimental techniques are introduced and demonstrated in order to optimize performance in certain areas and improve upon capabilities in respect to prism-based systems. Holographically fabricated gratings are characterized by atomic force microscopy and optical methods, aided by simulations and profile parameters responsible for efficient coupling are analyzed. The directional emission of fluorophores immobilized on a grating surface is studied in detail, including the magnitude and geometry of the fluorescence emission pattern for different grating constants and polarizations. Additionally, the separation between the minimum of the reflected intensity and the maximum fluorescence excitation position is examined. One of the key requirements for the commercial feasibility of grating coupling is the cheap and faithful mass production of disposable samples from a given master grating. The replication of gratings is demonstrated by a simple hot embossing method with good reproducibility to address this matter. The in-situ fluorescence detection of analyte immobilization and affinity measurements using grating coupling are described for the first time. The physical factors related to the sensitivity of the technique are assessed and the lower limit of detection of the technique is determined for an exemplary assay. Particular attention is paid to the contribution of bulk fluorophores to the total signal in terms of magnitude and polarization of incident and emitted light. Emission from the bulk can be a limiting factor for experiments with certain assay formats. For that reason, a novel optical method, based on the modulation of both polarization and intensity of the incident beam, is introduced and demonstrated to be capable of eliminating this contribution.

Eigenschaftskorrelationen in kolloidalen Festkörpern und Fluiden aus optischen Experimenten

Die Arbeit beschäftigt sich mit ein- und zweikomponentigen, geladenen Kolloidsystemen, die in vollentsalzten wässrigen und organischen Dispersionen kristalline Strukturen ausbilden. Im ersten Teil der Arbeit wird die Wechselwirkung der Kolloide mit verschiedenen Methoden charakterisiert. Dabei zeigten sich quantitative Übereinstimmungen zwischen den Resultaten aus Zellenmodellrechnungen und aus elektrokinetischen Messungen einerseits und Messungen des Phasenverhaltens und der Elastizität andererseits. Diese nunmehr gut gesicherten Diskrepanzen und Korrelationen bedürfen des theoretischen Verständnisses. Im zweiten Teil der Arbeit wurde das Erstarrungsverhalten kolloidaler Scherschmelzen in den kristallinen Zustand mit (zeitaufgelöster) statischer Lichtstreuung und mikroskopischen Methoden untersucht. Dies erlaubte zunächst die kritische Überprüfung klassischer Modelle zur Kristallisationskinetik (Wilson- Frenkel- Gesetz, klassische Nukleationstheorie, Kolmogorov- Johnson- Mehl- Avrami (KJMA)- Modell). Es zeigte sich, dass diese Modelle gut geeignet sind die Verfestigung auch geladener kolloidaler Schmelzen zu beschreiben, wenn die diffusive Einteilchendynamik korrekt berücksichtigt wird. Erstmals wurden Oberflächenspannungen zwischen Kristallkeim und Schmelze für geladene Systeme bestimmt, die im Gegensatz zu Hartkugel- Systemen eine lineare Zunahme mit der Partikelkonzentration aufweisen. Der Methodenpark und die Auswerteverfahren wurden sodann auf binäre kolloidale Mischungen übertragen. Entsprechend den Einzelkomponenten kristallisieren alle Mischungen in einer kubischen Struktur. Leitfähigkeitsmessungen und Elastizität stehen meist im Einklang mit der Nukleation zufallsgeordneter Substitutionskristalle. Für mehrere Proben mit unterschiedlichen Größenverhältnissen wurde mit statischer Lichtstreuung der Einfluss der Komposition und der Partikelkonzentration auf das Nukleationsverhalten untersucht. Im Allgemeinen wurde das Nukleationsszenario einkomponentiger Systeme mit einigen unerwarteten, quantitativen Unterschieden reproduziert. Für eine Probe, die eine Kompositionsordnung andeutet, wurden interessante Korrelationen zwischen der Nukleationskinetik und den Eigenschaften des resultierenden Festkörpers gefunden.

Strukturbildungsverhalten kettensteifer Polyelektrolyte in wässrigen Lösungen am Beispiel von Poly(para-phenylen)sulfonat

An einer Vielzahl biogener Polyelektrolyte, wie z.B. den Nukleinsäuren DNA und RNA sowie Proteinen, ist die Ausbildung von Strukturhierarchien durch Selbstorganisation von Strukturelementen zu beobachten. Dabei wird das Strukturbildungsverhalten durch eine Kopplung von Wechselwirkungen auf verschiedenen Längenskalen, den kurzreichweitigen ausgeschlossenen Volumen und den langreichweitigen elektrostatischen Wechselwirkungen (Coulomb-Wechselwirkungen), die wiederum durch eine Vielzahl mikroskopische Parameter (z.B. Konformation) beeinflusst werden, bestimmt. Durch diese Komplexität ist es nicht möglich, den für die Strukturbildung hochgeladener Systeme bedeutsamen Beitrag der elektrostatischen Wechselwirkungen isoliert zu betrachten. Aus diesem Grund werden zur Aufklärung von Wechselwirkungs- und Strukturbildungsmechanismen vereinfachte Modell-Systeme herangezogen. Eine Möglichkeit besteht in der Verwendung synthetischer, kettensteifer Polyelektrolyte. Im Rahmen dieser Arbeit wurde das Aggregationsverhalten wässriger Lösungen dodecylsubstituierter Poly(para-phenylen)sulfonate (PPPS) sowie die Beeinflussung der Strukturbildung durch verschiedene Parameter charakterisiert. Als Einflussparameter wurden einerseits die Gegenion-Spezies und andererseits die Temperatur- und Konzentrations-Abhängigkeit untersucht. Hierzu wurden wässrige Lösungen der freien Säuren der PPPS mit Molekulargewichten zwischen MW = 18 kg/mol bis 58 kg/mol mittels Licht-, Röntgen- und Neutronenstreuung sowie durch Licht-, Polarisations-, Transmissionselektronen- und Rasterkraftmikroskopie in einem Konzentrationsbereich von 0,0008 < c < 1,1 g/L untersucht.

Advanced SPM studies on the growth of ultrathin films of organic semiconductors at metal and dielectric interfaces

Many studies on the morphology, molecular orientation, device performance, substrate nature and growth parameter dependence have been carried out since the proposal of Sexithiophene (6T) for organic electronics [ ] However, these studies were mostly performed on films thicker than 20nm and without specifically addressing the relationship between morphology and molecular orientation within the nano and micro structures of ultrathin films of 0-3 monolayers. In 2004, the observation that in OFETs only the first few monolayers at the interface in contact with the gate insulator contribute to the charge transport [ ], underlined the importance to study submonolayer films and their evolution up to a few monolayers of thickness with appropriate experimental techniques. We present here a detailed Non-contact Atomic Force Microscopy and Scanning Tunneling Microscopy study on various substrates aiming at the investigation of growth mechanisms. Most reported similar studies are performed on ideal metals in UHV. However it is important to investigate the details of organic film growth on less ideal and even technological surfaces and device testpatterns. The present work addresses the growth of ultra thin organic films in-situ and quasi real-time by NC-AFM. An organic effusion cell is installed to evaporate the organic material directly onto the SPM sample scanning stage.

New platforms for optical biosensing

Physicochemical experimental techniques combined with the specificity of a biological recognition system have resulted in a variety of new analytical devices known as biosensors. Biosensors are under intensive development worldwide because they have many potential applications, e.g. in the fields of clinical diagnostics, food analysis, and environmental monitoring. Much effort is spent on the development of highly sensitive sensor platforms to study interactions on the molecular scale. In the first part, this thesis focuses on exploiting the biosensing application of nanoporous gold (NPG) membranes. NPG with randomly distributed nanopores (pore sizes less than 50 nm) will be discussed here. The NPG membrane shows unique plasmonic features, i.e. it supports both propagating and localized surface plasmon resonance modes (p SPR and l-SPR, respectively), both offering sensitive probing of the local refractive index variation on/in NPG. Surface refractive index sensors have an inherent advantage over fluorescence optical biosensors that require a chromophoric group or other luminescence label to transduce the binding event. In the second part, gold/silica composite inverse opals with macroporous structures were investigated with bio- or chemical sensing applications in mind. These samples combined the advantages of a larger available gold surface area with a regular and highly ordered grating structure. The signal of the plasmon was less noisy in these ordered substrate structures compared to the random pore structures of the NPG samples. In the third part of the thesis, surface plasmon resonance (SPR) spectroscopy was applied to probe the protein-protein interaction of the calcium binding protein centrin with the heterotrimeric G-protein transducin on a newly designed sensor platform. SPR spectroscopy was intended to elucidate how the binding of centrin to transducin is regulated towards understanding centrin functions in photoreceptor cells.

Nuclear structure studies in the xenon and radon region and the discovery of a new radon isotope by Penning trap mass spectrometry

Heutzutage gewähren hochpräzise Massenmessungen mit Penning-Fallen tiefe Einblicke in die fundamentalen Eigenschaften der Kernmaterie. Zu diesem Zweck wird die freie Zyklotronfrequenz eines Ions bestimmt, das in einem starken, homogenen Magnetfeld gespeichert ist. Am ISOLTRAP-Massenspektrometer an ISOLDE / CERN können die Massen von kurzlebigen, radioaktiven Nukliden mit Halbwertszeiten bis zu einigen zehn ms mit einer Unsicherheit in der Größenordnung von 10^-8 bestimmt werden. ISOLTRAP besteht aus einem Radiofrequenz-Quadrupol zum akkumulieren der von ISOLDE gelieferten Ionen, sowie zwei Penning-Fallen zum säubern und zur Massenbestimmung der Ionen. Innerhalb dieser Arbeit wurden die Massen von neutronenreichen Xenon- und Radonisotopen (138-146Xe und 223-229Rn) gemessen. Für elf davon wurde zum ersten Mal die Masse direkt bestimmt; 229Rn wurde im Zuge dieses Experimentes sogar erstmalig beobachtet und seine Halbwertszeit konnte zu ungefähr 12 s bestimmt werden. Da die Masse eines Nuklids alle Wechselwirkungen innerhalb des Kerns widerspiegelt, ist sie einzigartig für jedes Nuklid. Eine dieser Wechselwirkungen, die Wechselwirkung zwischen Protonen und Neutronen, führt zum Beispiel zu Deformationen. Das Ziel dieser Arbeit ist eine Verbindung zwischen kollektiven Effekten, wie Deformationen und Doppeldifferenzen von Bindungsenergien, sogenannten deltaVpn-Werten zu finden. Insbesondere in den hier untersuchten Regionen zeigen deltaVpn-Werte ein sehr ungewöhnliches Verhalten, das sich nicht mit einfachen Argumenten deuten lässt. Eine Erklärung könnte das Auftreten von Oktupoldeformationen in diesen Gebieten sein. Nichtsdestotrotz ist eine quantitative Beschreibung von deltaVpn-Werten, die den Effekt von solchen Deformationen berücksichtigt mit modernen Theorien noch nicht möglich.

Messung dynamischer Prozesse in der Nähe von Grenzflächen mit Hilfe neu entwickelter Lichtstreumethoden

Die vorliegende Arbeit behandelt die Entwicklung und Erprobung zweier neuer dynamischer Lichtstreumethoden: Die Resonanz verstärkte Lichtstreuung (REDLS: resonance enhanced dynamic light scattering) und die Wellenleiter verstärkte Lichtstreuung (WEDLS: waveguide enhanced dynamic light scattering). Beide Methoden verwenden eine Kombination aus evaneszenten Wellen und dynamischer Lichtstreuung: Bei der REDLS-Technik wird das evaneszentes Feld eines Oberflächenplasmons verwendet, bei der WEDLS-Technik handelt es sich um das evaneszente Feld von Metallfilm verstärkten Leckwellenleitermoden. Die neuen Methoden liefern Informationen über die Dynamik an Grenzflächen über ein breites Zeitfenster (einige Nanosekunden bis hin zu mehreren Sekunden) mit einer räumlichen Auflösung im sub-Mikrometerbereich. Sie erweitern somit das Gebiet der dynamischen Lichtstreuung in evaneszenter Geometrie, bei dem bislang nur die evanescent wave dynamic light scattering (EWDLS) - Technik zur Verfügung stand. Bei der EWDLS-Technik wird das evaneszente Feld der Totalreflexion als kohärenter Lichtstrahl für die dynamische Lichtstreuung verwendet. Ein Vergleich mit der EWDLS-Technik zeigt ein stark erhöhtes Signal/Rausch-Verhältnis bei den neu entwickelten Techniken aufgrund der resonanten Anregung. Zusätzlich ist es sowohl bei der REDLS- als auch bei der WEDLS-Technik möglich Grenzflächenmodifikationen und damit z.B. Adsorptionsprozesse zu detektieren. Der Einfluss einer Grenzfläche auf die Diffusion von PS-Latex-Partikeln wurde untersucht. Die Grenzfläche bestand im Fall der REDLS-Technik aus Gold, bei der WEDLS-Technik aus PMMA. Die Funktionsweise und die Gültigkeit der neu entwickelten Techniken wurde mit Hilfe von PS-Latex-Partikeln mit hydrodynamischen Radien von R =11nm bis hin zu R=204nm demonstriert.

Structure-property relations in polymers from renewable resources

The present research project focuses its attention on the study of structure-property relations in polymers from renewable sources (bio-based polymers) such as polymers microbially produced, i.e. polyhydrohyalkanoates (PHAs) or chemically synthesized using monomers from renewable sources, i.e. polyammide 11 (PA11). By means of a broad spectrum of experimental techniques, the influence of different modifications on bio-based polymers such as blending with other components, copolymerization with different co-monomers and introduction of branching to yield complex architectures have been investigated. The present work on PHAs focused on the study of the dependence of polymer properties on both the fermentation process conditions (e.g. bacterial strain and carbon substrate used) and the method adopted to recover PHAs from cells. Furthermore, a solvent-free method using an enzyme and chemicals in an aqueous medium, was developed in order to recover PHAs from cells. Such a method allowed to recover PHA granules in their amorphous state, i.e. in native form useful for specific applications (e.g. paper coating). In addition, a commercial PHA was used as polymeric matrix to develop biodegradable and bio-based composites for food packaging applications. Biodegradable, non-toxic, food contact plasticizers and low cost, widely available lignocellulosic fibers (wheat straw fibers) were incorporated in such a polymeric matrix, in order to decrease PHA brittleness and the polymer cost, respectively. As concerns the study of polyamide 11, both the rheological and the solid-state behavior of PA11 star samples with different arm number and length was studied. Introduction of arms in a polymer molecule allows to modulate melt viscosity behavior which is advantageous for industrial applications. Also, several important solid-state properties, in particular mechanical properties, are affected by the presence of branching. Given the importance of using ‘green’ synthetic strategies in polymer chemistry, novel poly(-amino esters), synthesized via enzymatic-catalyzed polymerization, have also been investigated in this work.

Charge generation, transport and recombination in organic solar cells

This thesis presents a study of the charge generation, transport, and recombination processes in organic solar cells performed with time-resolved experimental techniques. Organic solar cells based on polymers can be solution-processed on large areas and thus promise to become an inexpensive source of renewable energy. Despite significant improvements of the power conversion efficiency over the last decade, the fundamental working principles of organic solar cells are still not fully understood. It is the aim of this thesis to clarify the role of different performance limiting processes in organic solar cells and to correlate them with the molecular structure of the studied materials, i.e. poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). By combining time-of-flight charge transport measurements, transient absorption spectroscopy, a newly developed experimental technique called time delayed double pulse experiment and drift-diffusion simulations a comprehensive analysis of the working principles of P3HT:PCBM solar cells could be performed. It was found that the molecular structure of P3HT (i.e. the regioregularity) has a pronounced influence on the morphology of thin films of pristine P3HT and of blends of P3HT with PCBM. This morphology in turn affected the charge transport properties as well as the charge generation and recombination kinetics. Well-ordered regioregular P3HT was found to be characterized by a high charge carrier mobility, efficient charge generation and low but field-dependent (non-geminate) recombination. Importantly, the charge generation yield was found to be independent of temperature and applied electric field as opposed to the expectations of the Onsager-Braun model that is commonly applied to describe the temperature and field dependence of charge generation in organic solar cells. These properties resulted in a reasonably good power conversion efficiency. In contrast to this, amorphous regiorandom P3HT was found to show poor charge generation, transport and recombination properties that combine to a much lower power conversion efficiency.

Stress & structure of thin polymer brush films

Polymer brushes have unique properties with a large variety of possible applications ranging from responsive coatings and drug delivery to lubrication and sensing. For further development a detailed understanding of the properties is needed. Established characterization methods, however, only supply information of the surface. Experimental data about the inner “bulk” structure of polymer brushes is still missing.rnScattering methods under grazing incidence supply structural information of surfaces as well as structures beneath it. Nanomechanical cantilevers supply stress data, which is giving information about the forces acting inside the polymer brush film. In this thesis these two techniques are further developed and used to deepen the understanding of polymer brushes. rnThe experimental work is divided into four chapters. Chapter 2 deals with the preparation of polymer brushes on top of nanomechanical cantilever sensors as well as large area sample by using a “grafting-to” technique. The further development of nanomechanical cantilever readout is subject of chapter 3. In order to simplify cantilever sensing, a method is investigated which allows one to perform multiple bending experiments on top of a single cantilever. To do so, a way to correlate different curvatures is introduced as well as a way to conveniently locate differently coated segments. In chapter 4 the change in structure upon solvent treatment of mixed polymer brushes is investigated by using scattering methods and nanomechanical cantilevers amongst others. This allows one to explain the domain memory effect, which is typically found in such systems. Chapter 5 describes the implementation of a phase shifting interferometer - used for readout of nanomechanical cantilevers - into the µ-focused scattering beamline BW4, allowing simultaneous measurements of stress and structure information. The last experimental chapter 6 deals with the roughness correlation in polymer brushes and its dependence on the chain tethered density.rnIn summary, the thesis deals with utilization of new experimental techniques for the investigation of polymer brushes and further development of the techniques themselves.rn

Organic lasing: correlation between molecular structure, optical and optoelectronic properties

In this thesis mainly two alternating indenofluorene-phenanthrene copolymers were investigated with a variety of spectroscopic and optoelectronic experiments. The different experimental techniques allowed to retrieve deeper insights into their unique optical as well as optoelectronic properties. The motivation of the research presented in this work was to correlate their photophysical properties with respect to their application in electrically pumped lasing. This thesis begins with the description of optical properties studied by classical absorption and emission spectroscopy and successively describes an overall picture regarding their excited state dynamics occurring after photoexcitation studied by time-resolved spectroscopy. The different spectroscopic methods do not only allow to elucidate the different optical transitions occurring in this class of materials, but also contribute to a better understanding of exciton dynamics and exciton interaction with respect to the molecular structure as well as aggregation and photooxidation of the polymers. Furthermore, the stimulated emission properties were analyzed by amplified spontaneous emission (ASE) experiments. Especially one of the investigated materials, called BLUE-1, showed outstanding optical properties including a high optical gain, a low threshold for ASE and low optical losses. Apart from the optical experiments, the charge carrier mobility was measured with the time-of-flight technique and a comparably high hole mobility on the order of 1 x 10-² cm²/(Vs) was determined for BLUE-1 which makes this material promising for organic lasing. The impact of the high charge carrier mobility in this material class was further analyzed in different optoelectronic devices such as organic LEDs (OLEDs) and organic solar cells.

Complex colloids by the emulsion solvent evaporation process

In this thesis, different complex colloids were prepared by the process of solvent evaporation from emulsion droplets (SEED). The term “complex” is used to include both an addressable functionality as well as the heterogeneous nature of the colloids.Firstly, as the SEED process was used throughout the thesis, its mechanism especially in regard to coalescence was investigated,. A wide variety of different techniques was employed to study the coalescence of nanodroplets during the evaporation of the solvent. Techniques such as DLS or FCS turned out not to be suitable methods to determine droplet coalescence because of their dependence on dilution. Thus, other methods were developed. TEM measurements were conducted on mixed polymeric emulsions with the results pointing to an absence of coalescence. However, these results were not quantifiable. FRET measurements on mixed polymeric emulsions also indicated an absence of coalescence. Again the results were not quantifiable. The amount of coalescence taking place was then quantified by the application of DC-FCCS. This method also allowed for measuring coalescence in other processes such as the miniemulsion polymerization or the polycondensation reaction on the interface of the droplets. By simulations it was shown that coalescence is not responsible for the usually observed broad size distribution of the produced particles. Therefore, the process itself, especially the emulsification step, needs to be improved to generate monodisperse colloids.rnThe Janus morphology is probably the best known among the different complex morphologies of nanoparticles. With the help of functional polymers, it was possible to marry click-chemistry to Janus particles. A large library of functional polymers was prepared by copolymerization and subsequent post-functionalization or by ATRP. The polymers were then used to generate Janus particles by the SEED process. Both dually functionalized Janus particles and particles with one functionalized face could be obtained. The latter were used for the quantification of functional groups on the surface of the Janus particles. For this, clickable fluorescent dyes were synthesized. The degree of functionality of the polymers was found to be closely mirrored in the degree of functionality of the surface. Thus, the marriage of click-chemistry to Janus particles was successful.Another complex morphology besides Janus particles are nanocapsules. Stimulus-responsive nanocapsules that show triggered release are a highly demanding and interesting system, as nanocapsules have promising applications in drug delivery and in self-healing materials. To achieve heterogeneity in the polymer shell, the stimulus-responsive block copolymer PVFc-b-PMMA was employed for the preparation of the capsules. The phase separation of the two blocks in the shell of the capsules led to a patchy morphology. These patches could then be oxidized resulting in morphology changes. In addition, swelling occurred because of the hydrophobic to hydrophilic transition of the patches induced by the oxidation. Due to the swelling, an encapsulated payload could diffuse out of the capsules, hence release was achieved.The concept of using block copolymers responsive to one stimulus for the preparation of stimulus-responsive capsules was extended to block copolymers responsive to more than one stimulus. Here, a block copolymer responsive to oxidation and a pH change as well as a block copolymer responsive to a pH change and temperature were studied in detail. The release from the nanocapsules could be regulated by tuning the different stimuli. In addition, by encapsulating stimuli-responsive payloads it was possible to selectively release a payload upon one stimulus but not upon the other one.In conclusion, the approaches taken in the course of this thesis demonstrate the broad applicability and usefulness of the SEED process to generate complex colloids. In addition, the experimental techniques established such as DC-FCCS will provide further insight into other research areas as well.