The dynamic structure factor for molecular chains with variable stiffness in a dilute solution is investigated. In the limit of small scattering vectors q only the overall translational motion of the macromolecules contributes to the dynamic structure factor. The translational diffusion coefficient D exhibits a chain length dependence D∼1/√L for flexible chains and D∼ln L/L+const/L for rodlike chains. For flexible chains there is an intermediate scattering vector regime in which the decay rate or spectral linewidth of the dynamic structure factor is proportional to q3 indicating that stretching modes are dominant. Such an intermediate scattering vector regime cannot be observed for semiflexible or rodlike chains. At large scattering vectors q/2p≳1.5, where 1/2p is the persistence length of the macromolecules, the chain stiffness becomes important for any kind of molecules, i.e., even for very flexible ones. The dynamic structure factor and the decay rate are compared with experimental results of quasielastic neutron and light scattering experiments on different natural and synthetic macromolecules. These experimental results are in good agreement with the theoretical predictions. Furthermore, we determine the persistence length of F-actin from a dynamic light scattering experiment.

The partition functions of discrete as well as continuous stiff molecular chains are calculated using the maximum entropy principle. The chain is described by mass points, and their connectivity is taken into account by harmonic constraints (flexible segments) in addition to the bending restrictions. For comparison and as a test of the formalism the freely rotating chain as well as the Kratky–Porod wormlike chain (rigid segments) are reexamined treating the bending restrictions as constraints. It is shown that the second moments for the chain of flexible segments agree exactly with those known from the freely rotating chain for the discrete as well as the continuous chain and for all stiffnesses. Moreover, the Green’s function for the continuous chain is determined, which allows to obtain any desired two point distribution function. The influence of various bending restrictions on equilibrium properties is discussed. Furthermore, a comparison to other existing models, especially the Harris and Hearst model, is given and the validity of the various models is examined.

We present in-depth studies of the size tunability and the self-assembly behavior of Janus cylinders possessing a phase segregation into two hemicylinders. The cylinders are prepared by cross-linking the lamella-cylinder morphology of a polystyrene-block-polybutadiene-block-poly(methyl methacrylate) block terpolymer. The length of the Janus cylinders can be adjusted by both the amplitude and the duration of a sonication treatment from the micro- to the nanometer length. The corona segregation into a biphasic particle is evidenced by selective staining of the PS domains with RuO(4) and subsequent imaging. The self-assembly behavior of these facial amphiphiles on different length scales is investigated combining dynamic light scattering (DLS), small-angle neutron scattering (SANS), and imaging procedures. Cryogenic transmission electron microscopy images of the Janus cylinders in THF, which is a good solvent for both blocks, exhibit unimolecularly dissolved Janus cylinders with a core-corona structure. These results are corroborated by SANS measurements. Supramolecular aggregation takes place in acetone, which is a nonsolvent for polystyrene, leading to the observation of fiber-like aggregates. The length of these fibers depends on the concentration of the solution. A critical aggregation concentration is found, under which unimolecularly dissolved Janus cylinders exist. The fibers are composed of 2-4 Janus cylinders, shielding the inner insoluble polystyrene hemicylinder against the solvent. Herein, the SANS data reveal a core-shell structure of the aggregates. Upon deposition of the Janus cylinders from more concentrated solution, a second type of superstructure is formed on a significantly larger length scale. The Janus cylinders form fibrillar networks, in which the pore size depends on the concentration and deposition time of the sample.

We report on the unexpected finding of nanoscale fibers with a diameter down to 25 nm that emerge from a polymer solution during a standard spin-coating process. The fiber formation relies upon the Raleigh-Taylor instability of the spin-coated liquid film that arises due to a competition of the centrifugal force and the Laplace force induced by the surface curvature. This procedure offers an attractive alternative to electrospinning for the efficient, simple, and nozzle-free fabrication of nanoscale fibers from a variety of polymer solutions.Polymer nanofibers are attractive building blocks for functional nanoscale devices. They are promising candidates for various applications, including filtration, protective clothing, polymer batteries, and sensors.1-4 Furthermore, their high surface-to-volume ratio renders them attractive as catalyst supports as well as in drug delivery and tissue engineering. [5][6][7][8] Electrospinning, one of the most established fiber fabrication methods, has attracted much attention due to the ease by which fibers with diameters ranging from 10 nm to 10 µm can be produced from natural or synthetic materials. [9][10][11] However, this method requires a dc voltage in the kV range and high fiber production rates are difficult to achieve because only a single fiber emerges from the nozzle of the pipet holding the polymer solution. 12 Here, we report a simple but efficient procedure enabling the parallel fabrication of a multitude of polymer fibers with regular morphology and diameters as small as 25 nm. It involves the application of drops of a polymer solution onto a standard spin coater, followed by fast rotation of the chuck, without the need of a mechanical constriction. The fiber formation relies upon the instability of the spin-coated liquid film that arises due to a competition of the centrifugal force and the Laplace force induced by the surface curvature. This Rayleigh-Taylor instability triggers the formation of thin liquid jets emerging from the outward driven polymer solution, yielding solid nanofibers after evaporation of the solvent. In addition to being simple, the spinning procedure offers several technologically relevant advantages, including the absence of the need of a mechanical constriction and the ability to yield hollow polymer beads, and is applicable to different types of polymers.We have focused on the formation of nanofibers made of poly-(methylmethacrylate) (PMMA), which can be regarded as a prototype system for other polymers. In the centrifugal spinning experiments, an aliquot of a PMMA polymer solution was placed in the middle of the chuck of a spincoater, which was then rotated at a speed of at least 3000 rotations per minute (rpm) for a few seconds ( Figure S1 Supporting Information). The typical volume and concentration of the applied PMMA solution was 2 mL and 5 wt% in chlorobenzene, respectively, with polymer molecular weights of the order of 10 4 kg/mol. After spinning, PMMA nanofibers were collected at the edge of the spin-coater. Their diamete...