Herein, various dispersions of MoS obtained by means of liquid phase exfoliation are spectroscopically, (spectro-) electrochemically, and microscopically characterized. At the core of these studies are transient absorption assays. Importantly, small-angle X-ray scattering measurements are employed to corroborate the exfoliated character of the MoS flakes in dispersion, on the one hand, and to correlate the results with TEM, AFM, and Raman characterization in the solid state, on the other. It is, then, demonstrated that transient absorption spectroscopy responds sensitively not only to changes in the sample preparation but also to instrumental and environmental parameters. It is documented that the spectroscopic features and their underlying lifetimes are tuneable on the femto-, pico-, and nanosecond scales by changing, for example, the centrifugation speed, the pump fluence, or the temperature. In other words, transient absorption spectroscopy provides an in situ method to quantitatively characterize liquid dispersions of MoS without facing the problems of reaggregated samples due to their drying for microscopic assays. The most far reaching results stem from resonantly and nonresonantly changing the pump fluence to characterize either single- or multiple-excited-state species such as excitons, trions, and bi-/multiexcitons and to follow their formation and deactivation pattern.

Long chain sodium polyacrylate polymers in dilute aqueous solution respond extremely sensitive to the addition of small, stoichiometric amounts of Ca2+ ions. Essential features of this response are a considerable shrinking of the coil dimensions and an additional sensitivity of the coil dimensions toward a change in temperature. To reveal details of this shrinking process, the conformational changes in response to the addition of alkaline earth cations at two different temperatures are investigated by means of light and neutron scattering and by AFM on the same samples, respectively. Partially collapsed coils at 15 °C were further shrunken and modified in shape by increasing the temperature to 30 °C. The scattering curves from the intermediates at 30 °C could successfully be interpreted with a pearl necklace model, which includes a low amount of pearls per polymer separated by 80 nm from each other. AFM investigations of adsorbed chains confirm the drastic conformational changes inferred to the system with the temperature increase by 15 °C. The results are considered to be one of the rare direct evidence for a pearl-necklace-like intermediate along the coil-to-globule transition of polyelectrolyte chains.

A detailed light scattering investigation is presented on dilute solutions of long chain sodium polyacrylate in the presence of Cu 2þ ions under conditions which are close to the precipitation threshold of the respective Cu 2þ -PA chains. The results are compared with literature data ( Eur. Phys. J E 2001, 5, 117-126) from the corresponding system in the presence of Ca 2þ ions. In all cases the solvent is a 0.1 M NaCl solution in water. The PA coils shrink considerably with increasing Cu 2þ concentration as the conditions approach the precipitation threshold. Yet, the extent of shrinking can not be driven as far as for the respective Ca 2þ -PA system, where fully collapsed sphere-like polymers had been observed at the threshold. Analysis of the aggregation process with time-resolved static light scattering reveals loose coil-like aggregate structures for Cu 2þ -PA aggregates and compact sphere-like aggregates for Ca 2þ -PA in accordance with the limiting shape of the respective shrunken single chains. The onset of Ca 2þ or Cu 2þ induced aggregation of PA chains at the precipitation threshold borders an intramolecular coil shrinking process. The transition of shrinking into aggregation occurs more readily with Cu 2þ -PA as it does with Ca 2þ -PA.

Bivalent lead ions as representative main group heavy metal cations form specific interactions with the negatively charged COO– residues of sodium polyacrylate chains in dilute aqueous solution. The interactions eventually lead to aggregation and precipitation of sodium polyacrylate chains partially neutralized with Pb2+ cations. The present work outlines a small-angle X-ray (SAXS) and light scattering study of the polyacrylate chains undergoing changes in coil conformation and successive aggregation while approaching and crossing the Pb2+-induced precipitation threshold. The study reveals a coil shrinking while approaching the precipitation threshold. Anomalous SAXS (ASAXS) complemented this information with a first insight into the spatial distribution of the Pb2+ cations captured by the polyacrylate chains together with a semiquantitative estimation of the amount of Pb2+ cations located within the collapsed domains of the shrinking chains. Conformational aspects of the shrinking coils could be established by means of model form factors of hybrid chains formed by a freely jointed chain of rods with spheres located on all or part of the joints. Development and application of the form factors of the pearl-necklace-like hybrid model chains and the use of quantitative analysis of ASAXS data are described and discussed in detail.

Callus formation is a critical step for successful fracture healing. Little is known about the molecular composition and mineral structure of the newly formed tissue in the callus. The aim was to evaluate the feasibility of small angle x-ray scattering (SAXS) to assess mineral structure of callus and cortical bone and if it could provide complementary information with the compositional analyses from Fourier transform infrared (FTIR) microspectroscopy. Femurs of 12 male Sprague-Dawley rats at 9 weeks of age were fractured and fixed with an intramedullary 1.1 mm K-wire. Fractures were treated with the combinations of bone morphogenetic protein-7 and/or zoledronate. Rats were sacrificed after 6 weeks and both femurs were prepared for FTIR and SAXS analysis. Significant differences were found in the molecular composition and mineral structure between the fracture callus, fracture cortex, and control cortex. The degree of mineralization, collagen maturity, and degree of orientation of the mineral plates were lower in the callus tissue than in the cortices. The results indicate the feasibility of SAXS in the investigation of mineral structure of bone fracture callus and provide complementary information with the composition analyzed with FTIR. Moreover, this study contributes to the limited FTIR and SAXS data in the field.