Quasielastic methods

The quasielastic method as developed by Schapery [26] is used in the development of the viscoelastic residual stress model. The use of the quasielastic method is motivated by the fact that the relaxation moduli are required in the viscoelastic analysis of residual stresses, whereas the experimental characterization of composite materials is usually in terms of the creep compliances. An excellent account of the development of the quasielastic method is given in [27]. The underlying restriction in the application of the quasielastic method is that the compliance response of the material shows little curvature when plotted versus log time [28]. Harper [27] shows excellent agreement between the quasielastic method and direct inversion for AS4/3510-6 graphite/epoxy composite. For most graphite/thermoset systems, the restrictions imposed by the quasielastic method are satisfied. 

Recently, the newly developed time-resolved quasielastic laser scattering (QELS) has been applied to follow the changes in the surface tension of the nonpolarized water nitrobenzene interface upon the injection of cetyltrimethylammonium bromide [34] and sodium dodecyl sulfate [35] around or beyond their critical micelle concentrations. As a matter of fact, the method is based on the determination of the frequency of the thermally excited capillary waves at liquid-liquid interfaces. Since the capillary wave frequency is a function of the surface tension, and the change in the surface tension reflects the ion surface concentration, the QELS method allows us to observe the dynamic changes of the ITIES, such as the formation of monolayers of various surfactants [34]. 

Dynamic surface tension has also been measured by quasielastic light scattering (QELS) from interfacial capillary waves [30]. It was shown that QELS gives the same result for the surface tension as the traditional Wilhelmy plate method down to the molecular area of 70 A. QELS has recently utilized in the study of adsorption dynamics of phospholipids on water-1,2-DCE, water-nitrobenzene and water-tetrachloromethane interfaces [31]. This technique is still in its infancy in liquid-liquid systems and its true power is to be shown in the near future. 

PAD (perturbed angular distribution) is a variation of PAC with nuclear excitation by a particle beam from an accelerator. QMS is quasielastic MdBbauer-spectroscopy, QNS is quasielastic neutron spectroscopy. For MOBbauer spectroscopy (MS), perturbed angular correlation (PAC), and /J-nuclear magnetic resonance (/3-NMR), the accessible SE jump frequencies are determined by the life time (rN) of the nuclear states involved in the spectroscopic process. Since NMR is a resonance method, the resonance frequency of the experiment sets the time window. With neutron scattering, the time window is determined by the possible energy resolution of the spectrometer as explained later. 

A series of monodisperse PMMA latexes was synthesized and characterized with respect to refractive index, percent solids, and solution density. The particle size of each latex was analyzed by several different instrumental methods. The methods used include DCP, SFFF, HDC, Quasielastic Light Scattering (QELS), TEM, and turbidity. 

The process of molecular diffusion may be viewed conceptionally as a sequence of jumps with statistically varying jump lengths and residence times. Information about the mean jump length /(P and the mean residence time t, which might be of particular interest for a deeper understanding of the elementary steps of catalysis, may be provided by spectroscopic methods, in particular by quasielastic neutron scattering (see next Section) and nuclear magnetic resonance (NMR). 

Inelastic and quasielastic neutron scattering have special advantages for studying certain of the motional properties of protonated or organic species within zeolites and related microporous materials. These advantages and various experimental methods are outlined, and illustrated by measurements of torsional vibrations and rotational diffusion of tetramethylammonium (TMA) cations occluded within zeolites TMA-sodalite, omega, ZK-4 and S APO-20. 

The results presented here show that neutron scattering is an invaluable tool for studying the important area of ions binding to aqueous polymer solutions. Neutron difference methods allow direct evidence polymer-ion binding to be observed. Further developments in neutron scattering techniques and instmmentation will lead to increased precision in the future. Quantitative neutron quasielastic measurements provide an additional useful tool allowing studies of the modifications of the water dynamics to be studied. 

There are macroscopic (uptake measurements, liquid chromatography, isotopic-transient experiments, and frequency response techniques), and microscopic techniques (nuclear magnetic resonance, NMR and quasielastic neutron spectrometry, QENS) to measure the gas diffusivities through zeolites. The macroscopic methods are characterized by the fact that diffusion occurs as the result of an applied concentration gradient on the other hand, the microscopic methods render self-diffusion of gases in the absence of a concentration gradient [67]. 

Papoular, R.J. and Livesey, A.K. (1989) Quasielastic neutron scattering data evaluation using the maximum entropy method. In J. Skilling (ed), Maximum Entropy and Bayesian Methods. Kluwer Academic Publishers, Dordrecht, pp. 163-173. 

The most important experimental techniques in this field are structural analyses by both X-ray and neutron diffraction methods, and infrared and Raman spectroscopic measurements. Less frequently used techniques are nuclear magnetic resonance, both broad band NMR spectroscopy and magic angle spinning methods (MAS), nuclear quadrupole resonance (NQR), inelastic and quasielastic neutron scattering, conductivity and permittivity measurements as well as thermal analyses such as difference thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetry (TG and DTG) for phase transition studies. 

Table 2 includes as well the results of recent diffusion studies by molecular dynamics (MD) calculations and by quasielastic neutron scattering. Both methods consider the process of self-diffusion and reflect the transport properties over diffusion paths of typically a few nanometers. In view of the satisfactory agreement with the PFG NMR data, there should be no doubt that genuine... 

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