Scattering, quasielastic

Comparing Eqs. (83), (84) and Eqs. (21), (22) it follows immediately that Rouse and Zimm relaxation result in completely different incoherent quasielastic scattering. These differences are revealed in the line shape of the dynamic structure factor or in the (3-parameter if Eq. (23) is applied, as well as in the structure and Q-dependence of the characteristic frequency. In the case of dominant hydrodynamic interaction, Q(Q) depends on the viscosity of the pure solvent, but on no molecular parameters and varies with the third power of Q, whereas with failing hydrodynamic interaction it is determined by the inverse of the friction per mean square segment length and varies with the fourth power of Q. 

Quasielastic Scattering of a Star with Diblock Arms in Solution... 

In the case of solutions, concentration fluctuations only contribute to the central elastic part of the scattering spectrum. However, the Brownian movement of solute molecules creates weak frequency displacements that broaden the central peak. This phenomenon is called Rayleigh line broadening or quasielastic scattering [26-28]. This section deals with elastic scattering only. 

Dynamic processes at thermodynamic equilibrium that occur within a time range from sub-microseconds to seconds can be probed without the imposition of a transient disturbance by optical intensity fluctuation spectroscopy. As such, dynamic light scattering (DLS) [155] measures the fluctuation of quasielastic scattering intensity and fluorescence correlation spectroscopy (FCS) [156-158] measures concentration fluctuations of specific fluorescent molecules... 

Ahlrichs P, Diinweg B (1999) Simulation of a single polymer chain in solution by combining lattice Boltzman and molecular dynamics. J Chem Phys lll(17) 8225-8239 Akcasu Z, Gurol H (1976) Quasielastic scattering by dilute polymer solutions. J Polym Sci Polym Phys Ed 46(1) 1-10... 

The dynamics of bulk polymers have been approached in two different ways. On one hand, models of localized conformational jumps have been proposed to interpret numerous NMR experiments (see e.g. Ref. or . These models, which are specific of a given polymer assume that a short chain sequence performs conforpia-tional jumps between a few number of sites, the rest of the chain being immobile. Such localized jumps would lead to a well separated elastic peak in neutron quasielastic scattering experiments, in contradiction with all the experimental data obtained from polymer meltsIndeed, these models can in some cases be invoked to describe secondary relaxations in glassy polymers, but they are not sufficient to account for the numerous liquid-like properties of polymer melts. 

The picosecond internal dynamics of myoglobin was explored by measuring inelastic neutron scattering by Smith et al. [25]. At low temperatures they found the dynamics to be harmonic while at higher temperatures a considerable quasielastic scattering was detected. Agreement between the experimentally observed spectra and that calculated from molecular dynamics simulations also showed evidence for restriction of the conformational space sampled at 80 K relative to 300 K. On the basis of these results it was concluded that the protein is trapped in local minima at low temperatures in accord with the multiple substate model suggested by low temperature flash photolysis experiments and previous molecular dynamics simulations. Comparison of atomic fluctuation data sets collected at both 325 K and 80 K confirms that the room temperature... 

NHT The barriers to rotation for the NH4 ion in the ordered and disordered phases of NH4C1 and NH4Br have been calculated from their torsional frequencies and the results compared with the activation energies determined from n.m.r. results.46 Neutron quasielastic scattering has been used to probe the reorientations of NH4 ion in a single crystal of ammonium bromide.47 A Raman study of the phase transitions in NH4Br has been undertaken over a range of temperature and pressure. It was found that the ordered phase On is cubic, and that in this phase the NHJ ions are ordered.48... 

In previous papers we have reported on some detailed studies on the behaviour of the order parameter C, (T) which was assimilated to the correlation length for critical fluctuations accessible by means of neutron small-angle scattering as well some measurements on the molecular dynamics across the two phase transitions as explored by neutron quasielastic scattering as well as computer simulations. 

Fig. 5. Schematic of IQNS results with the elastic and quasielastic incoherent scattering of protons. Elastic scattering gives the geometry of the motion, while quasielastic scattering contains informations on the correlation times.

Hellweg, T., Brfilet, A. and Sottmann, T. (2000) Dynamics in an oil-continuous droplet microemulsions as seen by quasielastic scattering techniques. Phys. Chem. Chem. Phys., 2, 5168-5174. 

For better understanding of the present review, we include a brief account of the basic principles of inelastic and quasielastic scattering. For more detailed information and equations, the reader is referred to other books [31, 32]. 

Through the thickness dependence of elastic, inelastic, and quasielastic scattering in the millielectronvolt (or picosecond) region, it was found that the fast picosecond dynamics of polymer thin films was not described by homogenous dynamics but by heterogeneous dynamics, which were attributed to the orientation of molecular chains at the interface between polymer thin film and substrate. 

Novikov AG, Rodnikova MN, Savostin W, Sobolev OV (1994) Study of the diffusion of cesium ions in an aqueous solution of CsCl by a method of quasielastic scattering of slow neutrons. Zh FizKhim 68 1982-1986... 

The prefactor /, has also been associated with the Debye frequency of the lattice modes. The diffusion of H in the fee metals Pd, Ni, Cu and Al, reduced to the elementary hop rate between the neighbouring sites, shows classical behaviour (6.2) above room temperature . Note that many experimental methods, including neutron inelastic and quasielastic scattering, NMR line narrowing and spin-lattice relaxation, internal friction and ultrasonic damping, can give important information about the H motion on various timescales, that complements that obtained from ordinary diffusion measurements. 

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