Conjugated Polymers have attracted a great deal of research interest in recent years due to their optoelectronic properties which makes them suitable for applications in organic light-emitting devices (OLEDs) and organic photovoltaics. Their properties are strongly dependent on the electron-electron and electron-nuclear interactions as well as the disorder which is present in almost all systems at finite temperatures. In this thesis the optical properties of electronically neutral conjugated polymers will be investigated. The results obtained are general and applicable to a wide range of parameters. In order to compare these to experiment the optical properties of poly( paraphenylene), poly(para-phenylene vinylene), and derivatives have been calculated. In these polymers the primary photoexcitations are Frenkel excitons which can be described by the Frenkel-Holstein Hamiltonian, which explicitly takes into account the exciton-nuclear coupling. Disorder can be introduced into this model both as diagonal and off-diagonal disorder within the Hamiltonian. First the optical transitions in ordered, linear conjugated polymers are investigated. It is found that the length of the polymer has a direct spectroscopic signature in the emission spectrum. When off-diagonal disorder is introduced the excitons localise on portions of the chain and the length of these portions, the conjugation length, then shows a clear emission signature. As such, a disordered polymer can be described theoretically as a chain of shorter segments, which define chromophores in a polymer context. Following from these calculations the role of conformation was investigated and effects were observed that greatly determine the optical properties of non-linear polymers. Most notable the Herzberg-Teller effect, which renders symmetrically forbidden transitions weakly allowed and greatly affects the absorption and emission spectra. The signatures observed in these spectra allow the determination of the (coarse grained) conformation of the polymer, something that has been difficult to measure directly.

In der vorliegenden Arbeit wird die Mechanik von Netzwerken semiflexibler Polymere behandelt. Insbesondere wird der Zusammenhang zwischen der Steifigkeit des Einzelfilaments und der Steifigkeit des Gesamtnetzwerks experimentell untersucht. Der Hintergrund aktueller, einschlägiger theoretische Modelle wird zusammengefasst. Die Möglichkeiten und Limitierungen bisheriger experimenteller Modellsysteme werden diskutiert. Zur Untersuchung des eingangs genannten Zusammenhangs wird ein neuartiges, vielfältiges Modellsystem für semiflexible Polymere auf Basis von DNA Röhren eingeführt und umfassend auf Einzelfilament- und Netzwerkebene charakterisiert. Die Steifigkeit des Netzwerks lässt sich damit und unter Einsatz von Quervernetzern über einen weiten Bereich einstellen. Es zeigt sich, dass bisherige einschlägige Modelle in der korrekten Vorhersage des o.g. Zusammenhangs scheitern. Mögliche Auswege in der Modellierung werden skizziert, sowie konkrete, weitere Anwendungen der DNA Röhren benannt.:Chapter 1 Introduction Chapter 2 Background Section 2.1 Theoretical Models Section 2.2 Rheology Section 2.3 Experimental Model Systems Section 2.4 Existing G_0(l_p) Studies Chapter 3 Materials & Methods Section 3.1 Microscopy Section 3.2 Atomic Force Microscopy Section 3.3 Shear Rheology Section 3.4 Actin Section 3.5 DNA Assembly Section 3.6 Statistical Analysis Tools Chapter 4 Results Section 4.1 Persistence Length of Individual Filaments Section 4.2 Entangled Networks Section 4.3 Reptation Section 4.4 Inextensibility Section 4.5 Cross-Linked DNA n-Helix Tubes Chapter 5 Discussion Section 5.1 Limitations of Established Semiflexible Model Systems Section 5.2 DNA $n$-Helix Tubes as a Tunable Model System Section 5.3 Validation as an Entangled Semiflexible Model System Section 5.4 Impact on Existing Theories Section 5.5 DNA n-Helix Tubes as a Tunable Material Section 5.6 Summary Section 5.7 Outlook Chapter A Further Calculations Section A.1 Detailed Calculations on Worm-Like Chains. Chapter B Protocols Section B.1 Actin Section B.2 DNA n-Helix Tubes Chapter Bibliography Chapter List of Own Publications Chapter Acknowledgments Chapter Zusammenfassung nach §11(4) Promotionsordnung

<div> The folding and unfolding processes of poly-protein has been tremendously studied recently. The poly-protein dynamics under an external force can play an important role in addressing the issue of the mechanics of muscle tissue. In this research, we use a single-molecule technique: magnetic tweezers to observe the dynamics of 8-mer poly-protein L under different loads applied and then in different Tris-buffered salines. Our result shows that more protein domains unfold as the force load becomes larger. At 6, 7 and 8 pN loads, the poly-protein is most likely to stay in state 1, 3 and 6 with 1, 3 and 6 domains unfolded, respectively according to the probability distribution. This can be well explained by our constructed free energy-related model. The fit results give protein L parameters of persistence length of 0.4 nm, contour length of 18.8 nm and the unfolding energy of 6.5 kT, all in reasonable ranges based on previously reported literature.</div><div> Besides, we also find the dependency of transition rate on force load and salt. The poly-protein has lower transition rate at high force than at low force due to the free energy tilting effect since high force extremely decreases the possibility of protein unfolding that results in a huge drop in the total number of folding and unfolding events. This inverse proportion effect can also be seen in different TRIS-buffered salines (TRIS-150mM NaCl, TRIS-1M NaCl, and TRIS-1M KCl,). We explore the effect of salt concentration, when the concentration of NaCl is increased, the transition rate increases while the probability distribution remains almost the same, indicating the protein unfolding barrier is lowered without altering the overall energy landscape. We attribute this to, first, the charge shielding effect that more interactions between ions and water molecules occur, causing fewer water molecules available to interact with the charged part of protein than before, and, second, more direct interactions of ions with protein that might affect the electrostatic-related transition rate. Considering the effect of salt type, the two 1M alkali metal-chloride salines are compared. We conclude that ions with larger size have less effect on transition rate because ions with smaller size (Na+) can create stronger bonds with water that increase the interference on the protein interaction with water and can easier penetrate into protein to directly interact with the protein.</div>

Recent years have seen remarkable progress in our understanding of physical aging in nondisordered systems with slow, i.e. glassy-like dynamics. In many systems a single dynamical length L(t), that grows as a power-law of time t or, in much more complicated cases, as a logarithmic function of t, governs the dynamics out of equilibrium. In the aging or dynamical scaling regime, these systems are best characterized by two-times quantities, like dynamical correlation and response functions, that transform in a specific way under a dynamical scale transformation. The resulting dynamical scaling functions and the associated non-equilibrium exponents are often found to be universal and to depend only on some global features of the system under investigation. We discuss three different types of systems with simple and complex aging properties, namely reaction diffusion systems with a power growth law, driven diffusive systems with a logarithmic growth law, and a non-equilibrium polymer network that is supposed to capture important properties of the cytoskeleton of living cells. For the reaction diffusion systems, our study focuses on systems with reversible reaction diffusion and we study two-times functions in systems with power law growth. For the driven diffusive systems, we focus on the ABC model and a related domain model and measure two- times quantities in systems undergoing logarithmic growth. For the polymer network model, we explain in some detail its relationship with the cytoskeleton, an organelle that is responsible for the shape and locomotion of cells. Our study of this system sheds new light on the non- equilibrium relaxation properties of the cytoskeleton by investigating through a power law growth of a coarse grained length in our system. / Ph. D.

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Entangled polymeric fluids subjected to shear display a stress plateau through a range of shear rates. The formation of this plateau is often attributed to an entanglement-disentanglement transition in scientific literature. However, to our best knowledge in situ studies recovering the intermediate scattering function of polymer dynamics under shear have until now never been performed. This thesis documents the successful development of a high viscosity shear device whose interaction with polarized neutrons is small enough to allow use for Neutron Spin Echo spectroscopy. Further, first measurements towards the direct observation of the variation of the degree of entanglement throughout increasing shear are documented, albeit yet for too short Fourier times to measure beyond Rouse dynamics.

Telechelic associating polymer networks consist of polymer chains terminated by endgroups that have a different chemical composition than the polymer backbone. When dissolved in a solution, the endgroups cluster together to form aggregates. At low temperature, a strongly connected reversible network is formed and the system behaves like a gel. Telechelic networks are of interest since they are representative for biopolymer networks (e.g. F-actin) and are widely used in medical applications (e.g. hydrogels for tissue engineering, wound dressings) and consumer products (e.g. contact lenses, paint thickeners). In this thesis such systems are studied by means of a molecular dynamics/Monte Carlo simulation. At first, the system in rest is studied by means of graph theory. The changes in network topology upon cooling to the gel state, are characterized. Hereto an extensive study of the eigenvalue spectrum of the gel network is performed. As a result, an in-depth investigation of the eigenvalue spectra for spatial ER, scale-free, and small-world networks is carried out. Next, the gel under the application of a constant shear is studied, with a focus on shear banding and the changes in topology under shear. Finally, the relation between the gel transition and percolation is discussed.

This work is a numerical examination of a semiflexible polymer exposed to a disorder landscape consisting of hard disks. For a small parameter range and simple constraints it is known that disorder leads to structural transitions of the equilibrium properties of polymers. The scope of this work strongly extends this range by going to both high disorder densities and large stiffnesses of the polymers. The competing length scales of polymer stiffness and average distance between the obstacles of the potential along with the way of assembling the disorder lead to a wide range of effects such as crumpling and stretching of polymer configurations due to the disorder or a modulation of the polymer’s characterizing observables with the correlation function of the potential. The high accuracy results presented in this work have been obtained by means of sophisticated Monte Carlo simulations. The refinement of a rarely applied but highly promising method to a state of the art algorithm in connection with latest numerical techniques made it possible to investigate the impact of hard-disk disorder on semiflexible polymer conformations on a broad scale.