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The inelastic mean free path (IMFP) of electrons was determined experimentally for selected polyaniline and polyacetylene samples with Ag and Ni references using elastic peak electron spectroscopy (EPES). The surface composition was determined by XPS and density by helium pycnometry. The high resolution hemispherical ESA-31 and ADES-400 spectrometers were used for measurements in the energy range E = 0.5–3.0 keV and E =0.4 − 1.6 keV, respectively. The integrated elastic peak intensity ratios for sample and reference were calculated using the Monte Carlo (MC) algorithm based on the electron elastic scattering cross-sections database NIST SRD64 version 3.1 and applying TPP-2M IMFPs for polymers. Surface excitation parameters (SEP) and material parameters (ach) for polymers were determined, using the model of Chen, from comparison of measured and MC calculated elastic peak intensity ratios. These corrections proved to be efficient in decreasing the percentage deviations between the obtained IMFPs and the TPP-2M formula IMFPs. The elastic peak of hydrogen was observed in the EPES spectra of polymers. The experimental contribution of the hydrogen to the total elastic peak was 0.58%, while this value obtained from the MC simulations was 1.98%.

We use an elastic rod model with contact to study the extension versus rotation diagrams of single supercoiled DNA molecules. We reproduce quantitatively the supercoiling response of overtwisted DNA and, using experimental data, we get an estimation of the effective supercoiling radius and of the twist rigidity of B-DNA. We find that unlike the bending rigidity, the twist rigidity of DNA seems to vary widely with the nature and concentration of the salt buffer in which it is immerged.

Ziel des Dissertation war es, mit Hilfe von Computersimulationen Erkenntnisse über die topologische Struktur sowie die Deformationseigenschaften von polymeren Netzwerken zu erhalten. Zu diesem Zweck wurden computergenerierte Netzwerke optimiert in geschlossene Wege (Maschen) zerlegt. Die Überprüfung der Verschlauftheit der Maschen geschah mit Hilfe der algebraischen Knotentheorie. Mit dieser Methoden konnte gezeigt werden, dass für Netzwerke ein Crossover-Bereich für Entanglements existiert. Für Netzwerke mit einer Subkettenlänge von weniger als etwa 100 statistischen Segmenten konnte kein signifikanter Einfluss der Entanglements nachgewiesen werden. Für Netzwerke mit einer Subkettenlänge von 200 Segmenten überstieg die Zahl der topologischen Netzpunkte die Zahl der chemischen Netzpunkte deutlich. In einem zweiten Teil sollten energetische Beiträge zur rücktreibenden Kraft bei der Simulation eines Zug-Dehnungs-Experiments untersucht werden. Insbesondere sollte das Flory'sche Postulat von der Dehnungsunabhängigkeit des van-der-Waals-Anteils der rücktreibenden Kraft getestet werden. In der Simulation wurde ein statistisches Netzwerk einem Deformationsexperiment unterworfen, indem ein Hookesches Federpotential im Randbereich des Netzwerks implementiert wurde, das das Netzwerke schrittweise deformierte. Die Simulation zeigte, dass die van-der-Waals-Kraft für kleine Dehngrade den dominierenden Anteil der rücktreibenden Kraft darstellt. Das Ergebnis steht in klarem Wiederspruch zu dem Flory'schen Modell und zeigt, dass auch intermolekulare Beiträge bei einer umfassenden Beschreibung des Deformationsverhaltens eines Netzwerks berücksichtigt werden müssen., The aim of the Ph.D. thesis was to gain knowledge about the topological structure and the deformation properties of polymer networks by using computer simulations. Therefore computer generated networks were decomposed in an optimized way into closed paths (meshes). For each pair of meshes the type of entanglement was determined by using algebraic knot theory. The simulations showed that a crossover exists between networks with subchain length of less than 100 in which topological entanglements do not contribute significantly and networks with subchain lengths of 200 and more, in which the entanglements dominate the topological structure of the systems. Furthermore a significant difference between the topological structures of end-linked and of statistically crosslinked networks was detected. The results show that the end-linked systems have an by far more complex topological structure than the statistically crosslinked systems with the same average subchain length. The second part of the thesis aimed at determining the influence of energetic contributions to the retractive force of a polymer network during an uniaxial deformation. In detail the postulate of Flory was to be tested which said that the van-der-Waals energy between the chains remains unchanged during deformation and that therefore the van-der-Waals force does not contribute to the retractive force. In the simulation a statistically cross-linked network was subject to a harmonic spring potential which deformed the network. The retractive force was measured for the same network with and without applying van-der-Waals forces between the chains. The simulation showed that the van-der-Waals force dominates the retractive force for small extensions and vanishes for large extensions. This results clearly contradicts the Flory assumption and shows that intermolecular forces have to be taken into account in order to comprehensively describe the deformation behavior of a polymer network.