Scattering behavior static structure

The defining property of a structural glass transition is an increase of the structural relaxation time by more than 14 orders in magnitude without the development of any long-range ordered structure.1 Both the static structure and the relaxation behavior of the static structure can be accessed by scattering experiments and they can be calculated from simulations. The collective structure factor of a polymer melt, where one sums over all scattering centers M in the system... 

In the present study, we have made X-ray diffraction, neutron diffraction with isotopic substitution, and quasi-elastic neutron scattering measurements on highly concentrated aqueous solutions of lithium halides in a wide temperature range from room temperature to below glass transition temperature, from which the microscopic behaviors of the static structure and dynamic properties of the solutions are revealed with lowering temperature. The results obtained are discussed in connection with ice nucleation, anisotropic motion of water, crystallization, and the partial recovery of hydrogen bonds. 

These results confirm the observation that polyelectrolyte aqueous solutions show two separate decay modes in the autocorrelation function and support our contention that ionic polymer systems generally behave similarly in polar solvents [23], To support this, it may be added that similar dynamic scattering behavior was recently reported for another type of ionomer, polyurethane ionomer, dissolved in a polar solvent, dimethylacetamide (e = 38) [92], Finally, it should be stressed that the explanation given above for light scattering (both static and dynamic) behavior of salt-free polyelectrolytes is based on the major role of intermolecular electrostatic interactions in causing characteristic behavior. No intramolecular interactions are explicitly included to explain the behavior. This is in accord with our contention that much of the polyelectrolyte behavior, especially structure-related aspects, is determined by intermolecular interactions [23]. 

The simulated values of Sp q) as well as the Debye formula exhibit a typical behavior for small and intermediate -values. Irrespective of the specific statistics to be applied for the configurational average, the initial decay of the static structure factor is related to the characteristic size of the scattering object, i.e., to the radius of gyration of the polymer in our... 

The development of various techniques has led to important advances. The possibility to measure intermolecular and intercolloidal forces directly represents a qualitative change from the indirect way such forces had been inferred in the past from aggregation kinetics or from bulk properties such as the compressibility (deduced from small angle scattering) or phase behavior. Both static (i.e., equilibrium) and dynamic (e.g., viscous) forces can now be directly measured, providing information not only on the fundamental interactions in liquids but also on the structure... 

We have focused on only the static (i.e., the time-averaged) measurements of intensities so far. However, one can also obtain the dynamic structure factor (i.e., as a function of time) from scattering experiments. The dynamic structure factor can then be used as a probe of the rheological behavior of the dispersions discussed in Chapter 4. 

Polyelectrolyte behavior is exhibited by solutions of SPS in DMF, Fig. 12. At low polymer concentrations, the viscosity Increases as a result of repulsion between the unshielded anions, which Increases the hydrodynamic volume of the polymer. The structure of SPS in DMF solutions as determined by static and dynamic light scattering is also discussed in the chapter by Hara and Wu. 

These findings confirm the model of polydisperse systems of homogeneous spheres by exact fits of the static light scattering curves, the expected M a3 dependence for PEC homologues prepared at different polymer concentrations, and the asymptotic q 4 behavior of compact spheres. The quantitative information obtained shows that the concentration of the component solutions does not affect the internal structure of the PECs remarkably but controls their level of aggregation to a great extent. 

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