Tailoring molecular weight of the conjugated model polymer MEH-PPV and its structure-property relations

In der vorliegenden Arbeit wurden Struktur-Eigenschaftsbeziehungen des konjugierten Modell-Polymers MEH-PPV untersucht. Dazu wurde Fällungs-fraktionierung eingesetzt, um MEH-PPV mit unterschiedlichem Molekulargewicht (Mw) zu erhalten, insbesondere MEH-PPV mit niedrigem Mw, da dieses für optische Wellenleiterbauelemente optimal geeignet ist Wir konnten feststellen, dass die Präparation einer ausreichenden Menge von MEH-PPV mit niedrigem Mw und geringer Mw-Verteilung wesentlich von der geeigneten Wahl des Lösungsmittels und der Temperatur während der Zugabe des Fällungsmittels abhängt. Alternativ dazu wurden UV-induzierte Kettenspaltungseffekte untersucht. Wir folgern aus dem Vergleich beider Vorgehensweisen, dass die Fällungsfraktionierung verglichen mit der UV-Behandlung besser geeignet ist zur Herstellung von MEH-PPV mit spezifischem Mw, da das UV-Licht Kettendefekte längs des Polymerrückgrats erzeugt. 1H NMR and FTIR Spektroskopie wurden zur Untersuchung dieser Kettendefekte herangezogen. Wir konnten außerdem beobachten, dass die Wellenlängen der Absorptionsmaxima der MEH-PPV Fraktionen mit der Kettenlänge zunehmen bis die Zahl der Wiederholeinheiten n  110 erreicht ist. Dieser Wert ist signifikant größer als früher berichtet. rnOptische Eigenschaften von MEH-PPV Wellenleitern wurden untersucht und es konnte gezeigt werden, dass sich die optischen Konstanten ausgezeichnet reproduzieren lassen. Wir haben die Einflüsse der Lösungsmittel und Temperatur beim Spincoaten auf Schichtdicke, Oberflächenrauigkeit, Brechungsindex, Doppelbrechung und Wellenleiter-Dämpfungsverlust untersucht. Wir fanden, dass mit der Erhöhung der Siedetemperatur der Lösungsmittel die Schichtdicke und die Rauigkeit kleiner werden, während Brechungsindex, Doppelbrechung sowie Wellenleiter-Dämpfungsverluste zunahmen. Wir schließen daraus, dass hohe Siedetemperaturen der Lösungsmittel niedrige Verdampfungsraten erzeugen, was die Aggregatbildung während des Spincoatings begünstigt. Hingegen bewirkt eine erhöhte Temperatur während der Schichtpräparation eine Erhöhung von Schichtdicke und Rauhigkeit. Jedoch nehmen Brechungsindex und der Doppelbrechung dabei ab.rn Für die Schichtpräparation auf Glassubstraten und Quarzglas-Fasern kam das Dip-Coating Verfahren zum Einsatz. Die Schichtdicke der Filme hängt ab von Konzentration der Lösung, Transfergeschwindigkeit und Immersionszeit. Mit Tauchbeschichtung haben wir Schichten von MEH-PPV auf Flaschen-Mikroresonatoren aufgebracht zur Untersuchung von rein-optischen Schaltprozessen. Dieses Verfahren erweist sich insbesondere für MEH-PPV mit niedrigem Mw als vielversprechend für die rein-optische Signalverarbeitung mit großer Bandbreite.rn Zusätzlich wurde auch die Morphologie dünner Schichten aus anderen PPV-Derivaten mit Hilfe von FTIR Spektroskopie untersucht. Wir konnten herausfinden, dass der Alkyl-Substitutionsgrad einen starken Einfluss auf die mittlere Orientierung der Polymerrückgrate in dünnen Filmen hat.rn

Aggregation of hybrid molecules and film formation of colloidal monolayers

A unique characteristic of soft matter is its ability to self-assemble into larger structures. Characterizing these structures is crucial for their applications. In the first part of this work, I investigated DNA-organic hybrid material by means of Fluorescence Correlation Spectroscopy (FCS) and Fluorescence Cross-Correlation Spectroscopy (FCCS). DNA-organic hybrid materials, a novel class of hybrid materials composed of synthetic macromolecules and oligodeoxynucleotide segmenta, are mostly amphiphilic and can self-assemble into supramolecular structures in aqueous solution. A hybrid material of a fluorophore, perylenediimide (PDI), and a DNA segment (DNA-PDI) has been developed in Prof. A. Hermann’s group (University of Groningen). This novel material has the ability to form aggregates through pi-pi stacking between planar PDIs and can be traced in solution due to the fluorescence of PDI. I have determined the diffusion coefficient of DNA-PDI conjugates in aqueous solution by means of FCS. In addition, I investigated whether such DNA-PDIs form aggregates with certain structure, for instance dimers. rnOnce the DNA hybrid material self-assemble into supermolecular structures for instance into micelles, the single molecules do not necessarily stay in one specific micelle. Actually, a single molecule may enter and leave micelles constantly. The average residence time of a single molecule in a certain micelle depends on the nature of the molecule. I have chosen DNA-b-polypropylene oxide (PPO) as model molecules and investigated the residence time of DNA-b-PPO molecules in their according micelles by means of FCCS.rnBesides the DNA hybrid materials, polymeric colloids can also form ordered structures once they are brought to an air/water interface. Here, hexagonally densely packed monolayers can be generated. These monolayers can be deposited onto different surfaces as coating layers. In the second part of this work, I investigated the mechanical properties of such colloidal monolayers using micromechanical cantilevers. When a coating layer is deposited on a cantilever, it can modify the elasticity of the cantilever. This variation can be reflected either by a deflection or by a resonance frequency shift of the cantilever. In turn, detecting these changes provides information about the mechanical properties of the coating layer. rnIn the second part of this work, polymeric colloidal monolayers were coated on a cantilever and homogenous polymer films of a few hundred nanometers in thickness were generated from these colloidal monolayers by thermal annealing or organic vapor annealing. Both the film formation process and the mechanical properties of these resulting homogenous films were investigated by means of cantilever. rnElastic property changes of the coating film, for example upon absorption of organic vapors, induce a deflection of the cantilever. This effect enables a cantilever to detect target molecules, when the cantilever is coated with an active layer with specific affinity to target molecules. In the last part of this thesis, I investigated the applicability of suitably functionalized micromechanical cantilevers as sensors. In particular, glucose sensitive polymer brushes were grafted on a cantilever and the deflection of this cantilever was measured during exposure to glucose solution. rn

Effetti della viscoelasticità sulla misura dell’energia di adesione tra film di polietilene

Lo stretch film è una diffusa applicazione per imballaggio dei film in polietilene (PE), utilizzato per proteggere diversi prodotti di vari dimensioni e pesi. Una caratteristica fondamentale del film è la sua proprietà adesiva in virtù della quale il film può essere facilmente chiuso su se stesso. Tipicamente vengono scelti gradi lineari a bassa densità (LLDPE) con valori relativamente bassi di densità a causa delle loro buone prestazioni. Il mercato basa la scelta del materiale adesivo per tentativi piuttosto che in base alla conoscenza delle caratteristiche strutturali ottimali per l’applicazione. Come per i pressure sensitive adhesives, le proprietà adesive di film stretch in PE possono essere misurati mediante "peel testing". Esistono molti metodi standard internazionali ma i risultati di tali prove sono fortemente dipendenti dalla geometria di prova, sulla possibile deformazione plastica che si verificano nel peel arm(s), e la velocità e temperatura. Lo scopo del presente lavoro è quello di misurare l'energia di adesione Gc di film stretch di PE, su se stessi e su substrati diversi, sfruttando l'interpretazione della meccanica della frattura per tener conto dell'elevata flessibilità e deformabilità di tali film. Quindi, la dipendenza velocità/temperatura di Gc sarà studiata con riferimento diretto al comportamento viscoelastico lineare dei materiali utilizzati negli strati adesivi, per esplorare le relazioni struttura-proprietà che possono mettere in luce i meccanismi molecolari coinvolti nei processi di adesione e distacco. Nella presente caso, l’adesivo non è direttamente disponibile come materiale separato che può essere messo tra due superfici di prova e misurato per la determinazione delle sue proprietà. Il presupposto principale è che una parte, o fase, della complessa struttura semi-cristallina del PE possa funzionare come adesivo, e un importante risultato di questo studio può essere una migliore identificazione e caratterizzazione di questo "fase adesiva".

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

Tailoring, synthesis and structure-property relationships of 2,3-thienoimide based molecular materials

Organic molecular semiconductors are subject of intense research for their crucial role as key components of new generation low cost, flexible, and large area electronic devices such as displays, thin-film transistors, solar cells, sensors and logic circuits. In particular, small molecular thienoimide (TI) based materials are emerging as novel multifunctional materials combining a good processability together to ambipolar or n-type charge transport and electroluminescence at the solid state, thus enabling the fabrication of integrated devices like organic field effect transistors (OFETs) and light emitting transistor (OLETs). Given this peculiar combination of characteristics, they also constitute the ideal substrates for fundamental studies on the structure-property relationships in multifunctional molecular systems. In this scenario, this thesis work is focused on the synthesis of new thienoimide based materials with tunable optical, packing, morphology, charge transport and electroluminescence properties by following a fine molecular tailoring, thus optimizing their performances in device as well as investigating and enabling new applications. Investigation on their structure-property relationships has been carried out and in particular, the effect of different π-conjugated cores (heterocycles, length) and alkyl end chain (shape, length) changes have been studied, obtaining materials with enhanced electron transport capability end electroluminescence suitable for the realization of OFETs and single layer OLETs. Moreover, control on the polymorphic behaviour characterizing thienoimide materials has been reached by synthetic and post-synthetic methodologies, developing multifunctional materials from a single polymorphic compound. Finally, with the aim of synthesizing highly pure materials, simplifying the purification steps and avoiding organometallic residues, procedures based on direct arylation reactions replacing conventional cross-couplings have been investigated and applied to different classes of molecules, bearing thienoimidic core or ends, as well as thiophene and anthracene derivatives, validating this approach as a clean alternative for the synthesis of several molecular materials.

Analytical investigation of squeeze film dampers

Squeeze film damping effects naturally occur if structures are subjected to loading situations such that a very thin film of fluid is trapped within structural joints, interfaces, etc. An accurate estimate of squeeze film effects is important to predict the performance of dynamic structures. Starting from linear Reynolds equation which governs the fluid behavior coupled with structure domain which is modeled by Kirchhoff plate equation, the effects of nondimensional parameters on the damped natural frequencies are presented using boundary characteristic orthogonal functions. For this purpose, the nondimensional coupled partial differential equations are obtained using Rayleigh-Ritz method and the weak formulation, are solved using polynomial and sinusoidal boundary characteristic orthogonal functions for structure and fluid domain respectively. In order to implement present approach to the complex geometries, a two dimensional isoparametric coupled finite element is developed based on Reissner-Mindlin plate theory and linearized Reynolds equation. The coupling between fluid and structure is handled by considering the pressure forces and structural surface velocities on the boundaries. The effects of the driving parameters on the frequency response functions are investigated. As the next logical step, an analytical method for solution of squeeze film damping based upon Green’s function to the nonlinear Reynolds equation considering elastic plate is studied. This allows calculating modal damping and stiffness force rapidly for various boundary conditions. The nonlinear Reynolds equation is divided into multiple linear non-homogeneous Helmholtz equations, which then can be solvable using the presented approach. Approximate mode shapes of a rectangular elastic plate are used, enabling calculation of damping ratio and frequency shift as well as complex resistant pressure. Moreover, the theoretical results are correlated and compared with experimental results both in the literature and in-house experimental procedures including comparison against viscoelastic dampers.

Numerical modeling of the failure mechanisms in Si thin film anode for Li-ion batteries

In recent times, the demand for the storage of electrical energy has grown rapidly for both static applications and the portable electronics enforcing the substantial improvement in battery systems, and Li-ion batteries have been proven to have maximum energy storage density in all rechargeable batteries. However, major breakthroughs are required to consummate the requirement of higher energy density with lower cost to penetrate new markets. Graphite anode having limited capacity has become a bottle neck in the process of developing next generation batteries and can be replaced by higher capacity metals such as Silicon. In the present study we are focusing on the mechanical behavior of the Si-thin film anode under various operating conditions. A numerical model is developed to simulate the intercalation induced stress and the failure mechanism of the complex anode structure. Effect of the various physical phenomena such as diffusion induced stress, plasticity and the crack propagation are investigated to predict better performance parameters for improved design.

Selective ablation with UV lasers of a-Si:H thin film solar cells in direct scribing configuration

Monolithical series connection of silicon thin-film solar cells modules performed by laser scribing plays a very important role in the entire production of these devices. In the current laser process interconnection the two last steps are developed for a configuration of modules where the glass is essential as transparent substrate. In addition, the change of wavelength in the employed laser sources is sometimes enforced due to the nature of the different materials of the multilayer structure which make up the device. The aim of this work is to characterize the laser patterning involved in the monolithic interconnection process in a different configurations of processing than the usually performed with visible laser sources. To carry out this study, we use nanosecond and picosecond laser sources working at 355nm of wavelength in order to achieve the selective ablation of the material from the film side. To assess this selective removal of material has been used EDX (energy dispersive using X-ray) analysis

Ultra high frequency thin film saw devices

Durante los últimos años el flujo de datos en la transmisión que tiene lugar en los sistemas de comunicación ha aumentado considerablemente de forma que día a día se requieren más aplicaciones trabajando en un rango de frecuencias muy alto (3-30 GHz). Muchos de estos sistemas de comunicación incluyen dispositivos de onda acústica superficial (SAW) y por tanto se hace necesario el aumento de frecuencia a la que éstos trabajan. Pero este incremento de frecuencia de los dispositivos SAW no sólo es utilizado en los sistemas de comunicación, varios tipos de sensores, por ejemplo, aumentan su sensibilidad cuando la frecuencia a la que trabajan también lo hace. Tradicionalmente los dispositivos SAW se han fabricado sobre cuarzo, LiNbO3 y LiTaO3 principalmente. Sin embargo la principal limitación de estos materiales es su velocidad SAW. Además, debido a la alta temperatura a la que se depositan no pueden ser integrados en la tecnología de fabricación CMOS. El uso de la tecnología de capa delgada, en la que un material piezoeléctrico es depositado sobre un substrato, se está utilizando en las últimas décadas para incrementar la velocidad SAW de la estructura y poder obtener dispositivos trabajando en el rango de frecuencias requerido en la actualidad. Por otra parte, esta tecnología podría ser integrada en el proceso de fabricación CMOS. Durante esta tesis nos hemos centrado en la fabricación de dispositivos SAW trabajando a muy alta frecuencia. Para ello, utilizando la tecnología de capa delgada, hemos utilizado la estructura nitruro de aluminio (AlN) sobre diamante que permite conseguir velocidades SAW del sustrato que no se pueden alcanzar con otros materiales. El depósito de AlN se realizó mediante sputtering reactivo. Durante esta tesis se han realizado diferentes experimentos para optimizar dicho depósito de forma que se han obtenido los parámetros óptimos para los cuales se pueden obtener capas de AlN de alta calidad sobre cualquier tipo de sustrato. Además todo el proceso se realizó a baja temperatura para que el procesado de estos dispositivos pueda ser compatible con la tecnología CMOS. Una vez optimizada la estructura AlN/diamante, mediante litografía por haz de electrones se fabricaron resonadores SAW de tamaño nanométrico que sumado a la alta velocidad resultante de la combinación AlN/diamante nos ha permitido obtener dispositivos trabajando en el rango de 10-28 GHz con un alto factor de calidad y rechazo fuera de la banda. Estás frecuencias y prestaciones no han sido alcanzadas por el momento en resonadores de este tipo. Por otra parte, se han utilizado estos dispositivos para fabricar sensores de presión de alta sensibilidad. Estos dispositivos son afectados altamente por los cambios de temperatura. Se realizó también un exhaustivo estudio de cómo se comportan en temperatura estos resonadores, entre -250ºC y 250ºC (rango de temperaturas no estudiado hasta el momento) diferenciándose dos regiones una a muy baja temperatura en la que el dispositivo muestra un coeficiente de retraso en frecuencia (TCF) relativamente bajo y otra a partir de los -100ºC en la que el TCF es similar al observado en la bibliografía. Por tanto, durante esta tesis se ha optimizado el depósito de AlN sobre diamante para que sea compatible con la tecnología CMOS y permita el procesado de dispositivos trabajando a muy alta frecuencia con altas prestaciones para comunicaciones y sensores. ABSTRACT The increasing volume of information in data transmission systems results in a growing demand of applications working in the super-high-frequency band (3–30 GHz). Most of these systems work with surface acoustic wave (SAW) devices and thus there is a necessity of increasing their resonance frequency. Moreover, sensor application includes this kind of devices. The sensitivity of them is proportional with its frequency. Traditionally, quartz, LiNbO3 and LiTaO3 have been used in the fabrication of SAW devices. These materials suffer from a variety of limitations and in particular they have low SAW velocity as well as being incompatible with the CMOS technology. In order to overcome these problems, thin film technology, where a piezoelectric material is deposited on top of a substrate, has been used during the last decades. The piezoelectric/substrate structure allows to reach the frequencies required nowadays and could be compatible with the mass electronic production CMOS technology. This thesis work focuses on the fabrication of SAW devices working in the super-high-frequency range. Thin film technology has been used in order to get it, especially aluminum nitride (AlN) deposited by reactive sputtering on diamond has been used to increase the SAW velocity. Different experiments were carried out to optimize the parameters for the deposit of high quality AlN on any kind of substrates. In addition, the system was optimized under low temperature and thus this process is CMOS compatible. Once the AlN/diamond was optimized, thanks to the used e-beam lithography, nanometric SAW resonators were fabricated. The combination of the structure and the size of the devices allow the fabrication of devices working in the range of 10-28 GHz with a high quality factor and out of band rejection. These high performances and frequencies have not been reached so far for this kind of devices. Moreover, these devices have been used as high sensitivity pressure sensors. They are affected by temperature changes and thus a wide temperature range (-250ºC to 250ºC) study was done. From this study two regions were observed. At very low temperature, the temperature coefficient of frequency (TCF) is low. From -100ºC upwards the TCF is similar to the one appearing in the literature. Therefore, during this thesis work, the sputtering of AlN on diamond substrates was optimized for the CMOS compatible fabrication of high frequency and high performance SAW devices for communication and sensor application.

Liquid crystal temperature sensor based on a micrometric structure and a metallic nanometric layer

This letter presents a novel temperature sensor, which consists of an interdigitated comb electrode structure with a micrometric-scale size, nanometric metallic layer, and nematic liquid crystal (NLC) film. This sensor exploits the permittivity dependence of the NLC with temperature and principle of electrical conductivity above the percolation threshold in thin film metallic layers. The latter has been demonstrated to increase the temperature sensitivity considerably. The high impedance input reduces the power dissipation, and the high enough voltage output makes it easy to measure the output signal with high precision. The operation principle and fabrication process as well as the characterization of the temperature sensor are presented. Experimental results show that the device offers a sensitivity of 9 mV/°C and is dependent on the applied voltage. This is six times greater than the same structure without the use of a nanometric layer.

Effects of unique ion chemistry on thin-film growth by plasma–surface interactions

Plasma processing is a standard industrial method for the modification of material surfaces and the deposition of thin films. Polyatomic ions and neutrals larger than a triatomic play a critical role in plasma-induced surface chemistry, especially in the deposition of polymeric films from fluorocarbon plasmas. In this paper, low energy CF3+ and C3F5+ ions are used to modify a polystyrene surface. Experimental and computational studies are combined to quantify the effect of the unique chemistry and structure of the incident ions on the result of ion-polymer collisions. C3F5+ ions are more effective at growing films than CF3+, both at similar energy/atom of ≈6 eV/atom and similar total kinetic energies of 25 and 50 eV. The composition of the films grown experimentally also varies with both the structure and kinetic energy of the incident ion. Both C3F5+ and CF3+ should be thought of as covalently bound polyatomic precursors or fragments that can react and become incorporated within the polystyrene surface, rather than merely donating F atoms. The size and structure of the ions affect polymer film formation via differing chemical structure, reactivity, sticking probabilities, and energy transfer to the surface. The different reactivity of these two ions with the polymer surface supports the argument that larger species contribute to the deposition of polymeric films from fluorocarbon plasmas. These results indicate that complete understanding and accurate computer modeling of plasma–surface modification requires accurate measurement of the identities, number densities, and kinetic energies of higher mass ions and energetic neutrals.

Structure, gas-barrier properties and overall migration of poly(lactic acid) films coated with hydrogenated amorphous carbon layers

Hydrogenated amorphous carbon (a-C:H) films were grown on a poly(lactic acid) (PLA) substrate by means of a radiofrequency plasma-enhanced chemical vapour deposition (rf-PECVD) technique with different deposition times (5, 20 and 40 min). The main goal of this treatment was to increase the barrier properties of PLA, maintaining its original transparency and colour as well as controlling interactions with food simulants for packaging applications. Morphological, chemical, and mechanical properties of PLA/a-C:H systems were evaluated while permeability and overall migration tests were performed in order to determine the effect of the plasma treatment on the gas-barrier properties of PLA films and their application in food packaging. Morphological results suggested a good adhesion of the deposited layers onto the polymer surface and the samples treated for 5 and 20 min only slightly darkened the PLA film. X-ray photoelectron spectroscopy revealed that the structural properties of the carbon layer deposited onto the PLA film depend on the exposure time. PLA/a-C:H system treated for 5 min showed the highest barrier properties, while none of the studied samples exceeded the migration limit established by the current legislation, suggesting the suitability of these materials in packaging applications.

Improving the photoactivity of bismuth vanadate thin film photoanodes through doping and surface modification strategies

Currently, one of the most attractive and desirable ways to solve the energy challenge is harvesting energy directly from the sunlight through the so-called artificial photosynthesis. Among the ternary oxides based on earth–abundant metals, bismuth vanadate has recently emerged as a promising photoanode. Herein, BiVO4 thin film photoanodes have been successfully synthesized by a modified metal-organic precursor decomposition method, followed by an annealing treatment. In an attempt to improve the photocatalytic properties of this semiconductor material for photoelectrochemical water oxidation, the electrodes have been modified (i) by doping with La and Ce (by modifying the composition of the BiVO4 precursor solution with the desired concentration of the doping element), and (ii) by surface modification with Au nanoparticles potentiostatically electrodeposited. La and Ce doping at concentrations of 1 and 2 at% in the BiVO4 precursor solution, respectively, enhances significantly the photoelectrocatalytic performance of BiVO4 without introducing important changes in either the material structure or the electrode morphology, according to XRD and SEM characterization. In addition, surface modification of the electrodes with Au nanoparticles further enhances the photocurrent as such metallic nanoparticles act as co-catalysts, promoting charge transfer at the semiconductor/solution interface. The combination of these two complementary ways of modifying the electrodes has resulted in a significant increase in the photoresponse, facilitating their potential application in artificial photosynthesis devices.

Pseudo-ternary phase diagrams of aqueous mixtures of Quil A, cholesterol and phospholipid prepared by the lipid-film hydration method

Pseudo-ternary phase diagrams of the polar lipids Quil A, cholesterol (Chol) and phosphatidylcholine (PC) in aqueous mixtures prepared by the lipid film hydration method (where dried lipid film of phospholipids and cholesterol are hydrated by an aqueous solution of Quil A) were investigated in terms of the types of particulate structures formed therein. Negative staining transmission electron microscopy and polarized light microscopy were used to characterize the colloidal and coarse dispersed particles present in the systems. Pseudo-ternary phase diagrams were established for lipid mixtures hydrated in water and in Tris buffer (pH 7.4). The effect of equilibration time was also studied with respect to systems hydrated in water where the samples were stored for 2 months at 4degreesC. Depending on the mass ratio of Quil A, Chol and PC in the systems, various colloidal particles including ISCOM matrices, liposomes, ring-like micelles and worm-like micelles were observed. Other colloidal particles were also observed as minor structures in the presence of these predominant colloids including helices, layered structures and lamellae (hexagonal pattern of ring-like micelles). In terms of the conditions which appeared to promote the formation of ISCOM matrices, the area of the phase diagrams associated with systems containing these structures increased in the order: hydrated in water/short equilibration period < hydrated in buffer/short equilibration period < hydrated in water/prolonged equilibration period. ISCOM matrices appeared to form over time from samples, which initially contained a high concentration of ring-like micelles suggesting that these colloidal structures may be precursors to ISCOM matrix formation. Helices were also frequently found in samples containing ISCOM matrices as a minor colloidal structure. Equilibration time and presence of buffer salts also promoted the formation of liposomes in systems not containing Quil A. These parameters however, did not appear to significantly affect the occurrence and predominance of other structures present in the pseudo-binary systems containing Quil A. Pseudo-ternary phase diagrams of PC, Chol and Quil A are important to identify combinations which will produce different colloidal structures, particularly ISCOM matrices, by the method of lipid film hydration. Colloidal structures comprising these three components are readily prepared by hydration of dried lipid films and may have application in vaccine delivery where the functionality of ISCOMs has clearly been demonstrated. (C) 2003 Elsevier B.V. All rights reserved.

Structure and thermal stability of Langmuir-Blodgett films of barium arachidate

The structures of multilayer Langmuir-Blodgett films of barium arachidate before and after heat treatment have been investigated using both atomic force microscopy (AFM) and grazing incidence synchrotron X-ray diffraction (GIXD). AFM gave information on surface morphology at molecular resolution while GIXD provided quantitative details of the lattice structures of the films with their crystal symmetries and lattice constants. As-prepared films contained three coexisting structures: two triclinic structures with the molecularchains tilted by about 20degrees from the film normal and with 3 x 1 or 2 x 2 super-lattice features arising from height modulation of the molecules in the films; a rectangular structure with molecules perpendicular to the film surface. Of these, the 3 x 1 structure is dominant with a loose correlation between the bilayers. In the film plane both superstructures are commensurate with the local structures, having different oblique symmetries. The lattice constants for the 3 x 1 structure are a(s) = 3a = 13.86 Angstrom, b(s) = b = 4.31 Angstrom and gamma(s) = gamma = 82.7degrees; for the 2 x 2 structure a(s) = 2a = 16.54 Angstrom, b(s) = 2b = 9.67 Angstrom, gamma(s) = gamma = 88degrees. For the rectangular structure the lattice constants are a = 7.39 Angstrom, b = 4.96 Angstrom and gamma = 90degrees. After annealing, the 2 x 2 and rectangular structures were not observed, while the 3 x 1 structure had developed over the entire film. For the annealed films the correlation length in the film plane is about twice that in the unheated films, and in the out-of-plane direction covers two bilayers. The above lattice parameters, determined by GIXD, differed significantly from the values obtained by AFM, due possibly to distortion of the films by the scanning action of the AFM tip. (C) 2004 Published by Elsevier B.V.