TY - JOUR A1 - Kietzke, Thomas A1 - Neher, Dieter A1 - Kumke, Michael Uwe A1 - Montenegro, Rivelino V. D. A1 - Landfester, Katharina A1 - Scherf, Ullrich T1 - A nanoparticle approach to control the phase separation in polyfluorene photovoltaic devices N2 - Polymer solar cell devices with nanostructured blend layers have been fabricated using single- and dual- component polymer nanospheres. Starting from an electron-donating and an electron-accepting polyfluorene derivative, PFB and F8BT, dissolved in suitable organic solvents, dispersions of solid particles with mean diameters of ca. 50 nm, containing either the pure polymer components or a mixture of PFB and F8BT in each particle, were prepared with the miniemulsion process. Photovoltaic devices based on these particles have been studied with respect to the correlation between external quantum efficiency and layer composition. It is shown that the properties of devices containing a blend of single-component PFB and F8BT particles differ significantly from those of solar cells based on blend particles, even for the same layer composition. Various factors determining the quantum efficiency in both kinds of devices are identified and discussed, taking into account the spectroscopic properties of the particles. An external quantum efficiency of ca. 4% is measured for a device made from polymer blend nanoparticles containing PFB:F8BT at a weight ratio of 1:2 in each individual nanosphere. This is among the highest values reported so far for photovoltaic cells using this material combination Y1 - 2004 ER - TY - THES A1 - Montenegro, Rivelino V. D. T1 - Crystallization, biomimetics and semiconducting polymers in confined systems T1 - Kristallisation, Biomimetik und halbleitende Polymere in räumlich begrenzten Systemen N2 - populärwissenschaftlicher Abstract: Kristallisation, Biomimetik und halbleitende Polymere in räumlich begrenzten Systemen: Öl und Wasser mischen sich nicht, man kann aber aus beiden Flüssigkeiten Emulsionen herstellen, bei denen Tröpfchen der einen Flüssigkeit in der anderen Flüssigkeit vorliegen. Das heißt, es können entweder Öltröpfchen in Wasser oder Wassertröpfchen in Öl erzeugt werden. Aus täglichen Erfahrungen, z.B. beim Kochen weiß man jedoch, dass sich eine Emulsion durch Schütteln oder Rühren herstellen lässt, diese jedoch nicht besonders stabil ist. Mit Hilfe von hohen Scherenergien kann man nun sehr kleine, in ihrer Größe sehr einheitliche und außerdem sehr stabile Tröpfchen von 1/10000 mm erhalten. Eine solche Emulsion wird Miniemulsion genannt. In der Dissertation wurden nun z.B. Miniemulsionen untersucht, die aus kleinen Wassertröpfchen in einem Öl bestehen. Es konnte gezeigt werden, dass das Wasser in diesen Tröpfchen, also in den räumlich begrenzten Systemen, nicht bei 0 °C, sondern bei -22 °C kristallisierte. Wie lässt sich das erklären? Wenn man einen Eimer Wasser hat, dann bildet sich normalerweise bei 0 °C Eis, da nämlich in dem Wasser einige (manchmal ganz wenige) Keime (z.B. Schutzteilchen, ein Fussel etc.) vorhanden sind, an denen sich die ersten Kristalle bilden. Wenn sich dann einmal ein Kristall gebildet hat, kann das Wasser im gesamten Eimer schnell zu Eis werden. Ultrareines Wasser würde bei -22 °C kristallisieren. Wenn man jetzt die Menge Wasser aus dem Eimer in kleine Tröpfchen bringt, dann hat man eine sehr, sehr große Zahl, nämlich 1017 Tröpfchen, in einem Liter Emulsion vorliegen. Die wenigen Schmutzpartikel verteilen auf sehr wenige Tröpfchen, die anderen Tröpfchen sind ultrarein. Daher kristallisieren sie erst bei -22 °C. Im Rahmen der Arbeit konnte auch gezeigt werden, dass die Miniemulsionen genutzt werden können, um kleine Gelatine-Partikel, also Nanogummibärchen, herzustellen. Diese Nanogummibärchen quellen bei Erhöhung der Temperatur auf ca. 38 °C an. Das kann ausgenutzt werden, um zum Beispiel Medikamente zunächst in den Partikeln im menschlichen Körper zu transportieren, die Medikamente werden dann an einer gewünschten Stelle freigelassen. In der Arbeit wurde auch gezeigt, dass die Gelatine-Partikel genutzt werden können, um die Natur nachzuahnen (Biomimetik). Innerhalb der Partikel kann nämlich gezielt Knochenmaterial aufgebaut werden kann. Die Gelatine-Knochen-Partikel können dazu genutzt werden, um schwer heilende oder komplizierte Knochenbrüche zu beheben. Gelatine wird nämlich nach einigen Tagen abgebaut, das Knochenmaterial kann in den Knochen eingebaut werden. LEDs werden heute bereits vielfältig verwendet. LEDs bestehen aus Halbleitern, wie z.B. Silizium. Neuerdings werden dazu auch halbleitende Polymere eingesetzt. Das große Problem bei diesen Materialien ist, dass sie aus Lösungsmitteln aufgebracht werden. Im Rahmen der Doktorarbeit wurde gezeigt, dass der Prozess der Miniemulsionen genutzt werden kann, um umweltfreundlich diese LEDs herzustellen. Man stellt dazu nun wässrige Dispersionen mit den Polymerpartikeln her. Damit hat man nicht nur das Lösungsmittel vermieden, das hat nun noch einen weiteren Vorteil: man kann nämlich diese Dispersion auf sehr einfache Art verdrucken, im einfachsten Fall verwendet man einfach einen handelsüblichen Tintenstrahldrucker. N2 - The colloidal systems are present everywhere in many varieties such as emulsions (liquid droplets dispersed in liquid), aerosols (liquid dispersed in gas), foam (gas in liquid), etc. Among several new methods for the preparation of colloids, the so-called miniemulsion technique has been shown to be one of the most promising. Miniemulsions are defined as stable emulsions consisting of droplets with a size of 50-500 nm by shearing a system containing oil, water, a surfactant, and a highly water insoluble compound, the so-called hydrophobe 1. In the first part of this work, dynamic crystallization and melting experiments are described which were performed in small, stable and narrowly distributed nanodroplets (confined systems) of miniemulsions. Both regular and inverse systems were examined, characterizing, first, the crystallization of hexadecane, secondly, the crystallization of ice. It was shown for both cases that the temperature of crystallization in such droplets is significantly decreased (or the required undercooling is increased) as compared to the bulk material. This was attributed to a very effective suppression of heterogeneous nucleation. It was also found that the required undercooling depends on the nanodroplet size: with decreasing droplet size the undercooling increases. 2. It is shown that the temperature of crystallization of other n-alkanes in nanodroplets is also significantly decreased as compared to the bulk material due to a very effective suppression of heterogeneous nucleation. A very different behavior was detected between odd and even alkanes. In even alkanes, the confinement in small droplets changes the crystal structure from a triclinic (as seen in bulk) to an orthorhombic structure, which is attributed to finite size effects inside the droplets. An intermediate metastable rotator phase is of less relevance for the miniemulsion droplets than in the bulk. For odd alkanes, only a strong temperature shift compared to the bulk system is observed, but no structure change. A triclinic structure is formed both in bulk and in miniemulsion droplets. 3. In the next part of the thesis it is shown how miniemulsions could be successfully applied in the development of materials with potential application in pharmaceutical and medical fields. The production of cross-linked gelatin nanoparticles is feasible. Starting from an inverse miniemulsion, the softness of the particles can be controlled by varying the initial concentration, amount of cross-link agent, time of cross-linking, among other parameters. Such particles show a thermo-reversible effect, e.g. the particles swell in water above 37 °C and shrink below this temperature. Above 37 °C the chains loose the physical cross-linking, however the particles do not loose their integrity, because of the chemical cross-linking. Those particles have potential use as drug carriers, since gelatin is a natural polymer derived from collagen. 4. The cross-linked gelatin nanoparticles have been used for the biomineralization of hydroxyapatite (HAP), a biomineral, which is the major constituent of our bones. The biomineralization of HAP crystals within the gelatin nanoparticles results in a hybrid material, which has potential use as a bone repair material. 5. In the last part of this work we have shown that layers of conjugated semiconducting polymers can be deposited from aqueous dispersion prepared by the miniemulsion process. Dispersions of particles of different conjugated semiconducting polymers such as a ladder-type poly(para-phenylene) and several soluble derivatives of polyfluorene could be prepared with well-controlled particle sizes ranging between 70 - 250 nm. Layers of polymer blends were prepared with controlled lateral dimensions of phase separation on sub-micrometer scales, utilizing either a mixture of single component nanoparticles or nanoparticles containing two polymers. From the results of energy transfer it is demonstrated that blending two polymers in the same particle leads to a higher efficiency due to the better contact between the polymers. Such an effect is of great interest for the fabrication of opto-electronic devices such as light emitting diodes with nanometer size emitting points and solar cells comprising of blends of electron donating and electron accepting polymers. KW - Confinement KW - miniemulsion KW - crystallization KW - biomimetics and semiconducting polymers Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-0000726 ER - TY - JOUR A1 - Asawapirom, Udom A1 - Bulut, F. A1 - Farrell, Tony A1 - Gadermaier, C. A1 - Gamerith, S. A1 - Güntner, Roland A1 - Kietzke, Thomas A1 - Patil, S. A1 - Piok, T. A1 - Montenegro, Rivelino V. D. A1 - Stiller, Burkhard A1 - Tiersch, Brigitte A1 - Landfester, Katharina A1 - List, E. J. W. A1 - Neher, Dieter A1 - Torres, C. S. A1 - Scherf, Ullrich T1 - Materials for polymer electronics applications semiconducting polymer thin films and nanoparticles N2 - The paper presents two different approaches to nanostructured semiconducting polymer materials: (i) the generation of aqueous semiconducting polymer dispersions (semiconducting polymer nanospheres SPNs) and their processing into dense films and layers, and (ii) the synthesis of novel semiconducting polyfluorene-block-polyaniline (PF-b-PANI) block copolymers composed of conjugated blocks of different redox potentials which form nanosized morphologies in the solid state Y1 - 2004 SN - 1022-1360 ER - TY - JOUR A1 - Kietzke, Thomas A1 - Stiller, Burkhard A1 - Landfester, Katharina A1 - Montenegro, Rivelino V. D. A1 - Neher, Dieter T1 - Probing the local optical properties of layers prepared from polymer nanoparticles N2 - It is well known that the performance of solar cells based on a blend of hole-accepting and electron-accepting conjugated polymers as the active material depend crucially on the length scale of the resulting phase separated morphology. However, a direct control of this morphology is difficult if the layer is prepared from an organic solvent. To circumvent this difficulty, recently a universal method to fabricate defined nano-structured blend layer using nanoparticles dispersed in water was demonstrated. These nanoparticles were prepared with the miniemulsion method, which allows for the preparation of semiconducting polymer nanospheres (SPNs) with diameters in the range of 30 to 300 nanometres. Since the process starts from the active material dissolved in a common solvent, it can be applied to the fabrication of nanoparticles of blends of polymers with oligomers or even with inorganic materials. We present here for the first time scanning near field optical microscopy (SNOM) investigations on these novel nanostructured polymer layers. We show that by spin-coating a mixture of two different dispersions a nanoparticle monolayer with a statistically distribution of the nanoparticles can be obtained. Mixing conjugated polymer nanoparticles with some inert particles like polystyrene beads may allow for the preparation of nano-sized light emitters Y1 - 2005 SN - 0379-6779 ER - TY - JOUR A1 - Landfester, Katharina A1 - Montenegro, Rivelino V. D. A1 - Scherf, Ullrich A1 - Günter, R. A1 - Asawapirom, Udom A1 - Patil, S. A1 - Neher, Dieter A1 - Kietzke, Thomas T1 - Semiconducting polymer nanospheres in aqeous dispersion prepared by a miniemulsion process Y1 - 2002 ER -