@phdthesis{Sinn2004,
  author    = {Sinn, Cornelia G.},
  title     = {Ion binding to polymers and lipid membranes in aqueous solutions : Ionenbindung an Polymeren und Lipidmembranen in w{\"a}ssrigen L{\"o}sungen},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-0001778},
  school      = {Universit{\"a}t Potsdam},
  year      = {2004},
  abstract  = {Ziel dieser Arbeit ist die Untersuchung der Ionenbindung an Polymeren und Lipidmembranen in w{\"a}ssrigen L{\"o}sungen. Im ersten Teil dieser Arbeit wurde der Einfluss verschiedener anorganischer Salze und Polyelektrolyte auf die Struktur des Wassers mit Hilfe Isothermer Mikrotitrationskalorimetrie (ITC) erforscht. Die Verd{\"u}nnungsw{\"a}rme der Salze wurde als Maß f{\"u}r die F{\"a}higkeit der Ionen, die geordnete Struktur des Wassers zu stabilisieren oder zu zerst{\"o}ren, verwendet. Die Verd{\"u}nnungsw{\"a}rmen konnten auf Hofmeister Effekte zur{\"u}ckgef{\"u}hrt werden. Im Anschluss daran wurde die Bindung von Ca2+ an Natrium- Poly(acryls{\"a}ure) (NaPAA) untersucht. Mit Hilfe von ITC und einer Ca2+- selektiven Elektrode wurde die Reaktionsenthalpie und Bindungsisotherme gemessen. Es wurde gezeigt, dass die Binding von Ca2+ - Ionen an NaPAA stark endotherm und daher entropiegetrieben ist. Anschließend wurde die Bindung von Ca2+ an die eindimensionale Polymerkette mit der an ein Lipidvesikel mit denselben funktioniellen Gruppen verglichen. Es wurde beobachtet, dass die Ionenbindung \–wie auch im Fall des Polymers- endotherm ist. Ein Vergleich der Ca2+- Bindung an die Lipidmembran mit der an das Polymer konnte zeigen, dass das Ion schw{\"a}cher an die Membran bindet. Im Zusammenhang mit diesen Experimenten wurde auch beobachtet, dass Ca2+ nicht nur an geladene, sondern auch an zwitterionische Lipidvesikel bindet. Schließlich wurde die Wechselwirkung zweier Salze, KCl and NaCl, mit einem neutralen Polymergel, PNIPAAM, und dem geladenen Polymer PAA untersucht. Mit Hilfe von Kalorimetrie und einer kaliumselektiven Elektrode wurde beobachtet, dass die Ionen mit beiden Polymeren wechselwirken, unabh{\"a}ngig davon, ob diese Ladungen tragen, oder nicht.},
  language  = {en}
}
@phdthesis{Prevot2006,
  author    = {Prevot, Michelle Elizabeth},
  title     = {Introduction of a thermo-sensitive non-polar species into polyelectrolyte multilayer capsules for drug delivery},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7785},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {The layer-by-layer assembly (LBL) of polyelectrolytes has been extensively studied for the preparation of ultrathin films due to the versatility of the build-up process. The control of the permeability of these layers is particularly important as there are potential drug delivery applications. Multilayered polyelectrolyte microcapsules are also of great interest due to their possible use as microcontainers. This work will present two methods that can be used as employable drug delivery systems, both of which can encapsulate an active molecule and tune the release properties of the active species. Poly-(N-isopropyl acrylamide), (PNIPAM) is known to be a thermo-sensitive polymer that has a Lower Critical Solution Temperature (LCST) around 32oC; above this temperature PNIPAM is insoluble in water and collapses. It is also known that with the addition of salt, the LCST decreases. This work shows Differential Scanning Calorimetry (DSC) and Confocal Laser Scanning Microscopy (CLSM) evidence that the LCST of the PNIPAM can be tuned with salt type and concentration. Microcapsules were used to encapsulate this thermo-sensitive polymer, resulting in a reversible and tunable stimuli- responsive system. The encapsulation of the PNIPAM inside of the capsule was proven with Raman spectroscopy, DSC (bulk LCST measurements), AFM (thickness change), SEM (morphology change) and CLSM (in situ LCST measurement inside of the capsules). The exploitation of the capsules as a microcontainer is advantageous not only because of the protection the capsules give to the active molecules, but also because it facilitates easier transport. The second system investigated demonstrates the ability to reduce the permeability of polyelectrolyte multilayer films by the addition of charged wax particles. The incorporation of this hydrophobic coating leads to a reduced water sensitivity particularly after heating, which melts the wax, forming a barrier layer. This conclusion was proven with Neutron Reflectivity by showing the decreased presence of D2O in planar polyelectrolyte films after annealing creating a barrier layer. The permeability of capsules could also be decreased by the addition of a wax layer. This was proved by the increase in recovery time measured by Florescence Recovery After Photobleaching, (FRAP) measurements. In general two advanced methods, potentially suitable for drug delivery systems, have been proposed. In both cases, if biocompatible elements are used to fabricate the capsule wall, these systems provide a stable method of encapsulating active molecules. Stable encapsulation coupled with the ability to tune the wall thickness gives the ability to control the release profile of the molecule of interest.},
  subject      = {Mikrokapsel},
  language  = {en}
}
@phdthesis{Nolte2006,
  author    = {Nolte, Marc},
  title     = {Integration of freestanding polyelectrolyte multilayer membranes in larger scale structures},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7355},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Ultrathin, semi-permeable membranes are not only essential in natural systems (membranes of cells or organelles) but they are also important for applications (separation, filtering) in miniaturized devices. Membranes, integrated as diffusion barriers or filters in micron scale devices need to fulfill equivalent requirements as the natural systems, in particular mechanical stability and functionality (e.g. permeability), while being only tens of nm in thickness to allow fast diffusion times. Promising candidates for such membranes are polyelectrolyte multilayers, which were found to be mechanically stable, and variable in functionality. In this thesis two concepts to integrate such membranes in larger scale structures were developed. The first is based on the directed adhesion of polyelectrolyte hollow microcapsules. As a result, arrays of capsules were created. These can be useful for combinatorial chemistry or sensing. This concept was expanded to couple encapsulated living cells to the surface. The second concept is the transfer of flat freestanding multilayer membranes to structured surfaces. We have developed a method that allows us to couple mm2 areas of defect free film with thicknesses down to 50 nm to structured surfaces and to avoid crumpling of the membrane. We could again use this technique to produce arrays of micron size. The freestanding membrane is a diffusion barrier for high molecular weight molecules, while small molecules can pass through the membrane and thus allows us to sense solution properties. We have shown also that osmotic pressures lead to membrane deflection. That could be described quantitatively.},
  subject      = {Polyelektrolyt},
  language  = {en}
}
@phdthesis{NarayananNair2006,
  author    = {Narayanan Nair, Arun Kumar},
  title     = {Molecular dynamics simulations of polyelectrolyte brushes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7005},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {This thesis studies strong, completely charged polyelectrolyte brushes. Extensive molecular dynamics simulations are performed on different polyelectrolyte brush systems using local compute servers and massively parallel supercomputers. The full Coulomb interaction of charged monomers, counterions, and salt ions is treated explicitly. The polymer chains are anchored by one of their ends to a uncharged planar surface. The chains are treated under good solvent conditions. Monovalent salt ions (1:1 type) are modelled same as counterions. The studies concentrate on three different brush systems at constant temperature and moderate Coulomb interaction strength (Bjerrum length equal to bond length): The first system consists of a single polyelectrolyte brush anchored with varying grafting density to a plane. Results show that chains are extended up to about 2/3 of their contour length. The brush thickness slightly grows with increasing anchoring density. This slight dependence of the brush height on grafting density is in contrast to the well known scaling result for the osmotic brush regime. That is why the result obtained by simulations has stimulated further development of theory as well as new experimental investigations on polyelectrolyte brushes. This observation can be understood on a semi-quantitative level using a simple scaling model that incorporates excluded volume effects in a free-volume formulation where an effective cross section is assigned to the polymer chain from where couterions are excluded. The resulting regime is called nonlinear osmotic brush regime. Recently this regime was also obtained in experiments. The second system studied consists of polyelectrolyte brushes with added salt in the nonlinear osmotic regime. Varying salt is an important parameter to tune the structure and properties of polyelectrolytes. Further motivation is due to a theoretical scaling prediction by Pincus for the salt dependence of brush thickness. In the high salt limit (salt concentration much larger than counterion concentration) the brush height is predicted to decrease with increasing external salt, but with a relatively weak power law showing an exponent -1/3. There is some experimental and theoretical work that confirms this prediction, but there are other results that are in contradiction. In such a situation simulations are performed to validate the theoretical prediction. The simulation result shows that brush thickness decreases with added salt, and indeed is in quite good agreement with the scaling prediction by Pincus. The relation between buffer concentration and the effective ion strength inside the brush at varying salt concentration is of interest both from theoretical as well as experimental point of view. The simulation result shows that mobile ions (counterions as well as salt) distribute nonhomogeneously inside and outside of the brush. To explain the relation between the internal ion concentration with the buffer concentration a Donnan equilibrium approach is employed. Modifying the Donnan approach by taking into account the self-volume of polyelectrolyte chains as indicated above, the simulation result can be explained using the same effective cross section for the polymer chains. The extended Donnan equilibrium relation represents a interesting theoretical prediction that should be checked by experimental data. The third system consist of two interacting polyelectrolyte brushes that are grafted to two parallel surfaces. The interactions between brushes are important, for instance, in stabilization of dispersions against flocculation. In the simulations pressure is evaluated as a function of separation D between the two grafting planes. The pressure behavior shows different regimes for decreasing separation. This behavior is in qualitative agreement with experimental data. At relatively weak compression the pressure behavior obtained in the simulation agrees with a 1/D power law predicted by scaling theory. Beyond that the present study could supply new insight for understanding the interaction between polyelectrolyte brushes.},
  subject      = {Molekulardynamik},
  language  = {en}
}
@phdthesis{Boroudjerdi2005,
  author    = {Boroudjerdi, Hoda},
  title     = {Charged polymer-macroion complexes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6282},
  school      = {Universit{\"a}t Potsdam},
  year      = {2005},
  abstract  = {This work explores the equilibrium structure and thermodynamic phase behavior of complexes formed by charged polymer chains (polyelectrolytes) and oppositely charged spheres (macroions). Polyelectrolyte-macroion complexes form a common pattern in soft-matter physics, chemistry and biology, and enter in numerous technological applications as well. From a fundamental point of view, such complexes are interesting in that they combine the subtle interplay between electrostatic interactions and elastic as well as entropic effects due to conformational changes of the polymer chain, giving rise to a wide range of structural properties. This forms the central theme of theoretical studies presented in this thesis, which concentrate on a number of different problems involving strongly coupled complexes, i.e. complexes that are characterized by a large adsorption energy and small chain fluctuations. In the first part, a global analysis of the structural phase behavior of a single polyelectrolyte-macroion complex is presented based on a dimensionless representation, yielding results that cover a wide range of realistic system parameters. Emphasize is made on the interplay between the effects due to the polyelectrolytes chain length, salt concentration and the macroion charge as well as the mechanical chain persistence length. The results are summarized into generic phase diagrams characterizing the wrapping-dewrapping behavior of a polyelectrolyte chain on a macroion. A fully wrapped chain state is typically obtained at intermediate salt concentrations and chain lengths, where the amount of polyelectrolyte charge adsorbed on the macroion typically exceeds the bare macroion charge leading thus to a highly overcharged complex. Perhaps the most striking features occur when a single long polyelectrolyte chain is complexed with many oppositely charged spheres. In biology, such complexes form between DNA (which carries the cell's genetic information) and small oppositely charged histone proteins serving as an efficient mechanism for packing a huge amount of DNA into the micron-size cell nucleus in eucaryotic cells. The resultant complex fiber, known as the chromatin fiber, appears with a diameter of 30~nm under physiological conditions. Recent experiments indicate a zig-zag spatial arrangement for individual DNA-histone complexes (nucleosome core particles) along the chromatin fiber. A numerical method is introduced in this thesis based on a simple generic chain-sphere cell model that enables one to investigate the mechanism of fiber formation on a systematic level by incorporating electrostatic and elastic contributions. As will be shown, stable complex fibers exhibit an impressive variety of structures including zig-zag, solenoidal and beads-on-a-string patterns, depending on system parameters such as salt concentration, sphere charge as well as the chain contour length (per sphere). The present results predict fibers of compact zig-zag structure within the physiologically relevant regime with a diameter of about 30~nm, when DNA-histone parameters are adopted. In the next part, a numerical method is developed in order to investigate the role of thermal fluctuations on the structure and thermodynamic phase behavior of polyelectrolyte-macroion complexes. This is based on a saddle-point approximation, which allows to describe the experimentally observed reaction (or complexation) equilibrium in a dilute solution of polyelectrolytes and macroions on a systematic level. This equilibrium is determined by the entropy loss a single polyelectrolyte chain suffers as it binds to an oppositely charged macroion. This latter quantity can be calculated from the spectrum of polyelectrolyte fluctuations around a macroion, which is determined by means of a normal-mode analysis. Thereby, a stability phase diagram is obtained, which exhibits qualitative agreement with experimental findings. At elevated complex concentrations, one needs to account for the inter-complex interactions as well. It will be shown that at small separations, complexes undergo structural changes in such a way that positive patches from one complex match up with negative patches on the other. Furthermore, one of the polyelectrolyte chains may bridge between the two complexes. These mechanisms lead to a strong inter-complex attraction. As a result, the second virial coefficient associated with the inter-complex interaction becomes negative at intermediate salt concentrations in qualitative agreement with recent experiments on solutions of nucleosome core particles.},
  subject      = {Biopolymere},
  language  = {en}
}