Ngai coupling model

The Ngai Coupling Model of Relaxation Generahzations, Alternatives, and their use in the Analysis of non-Arrhenius Conductivity in Glassy Fast-Ionic Materials, J. Appl. Phys. 84, 812-827. 

Figure 37 (a) Calculation of expansion side of the r-effective plot using the Ngai coupling model. The expansion gap is reproduced, (b) shows the shift factor a( T, used in the model vs. the experimental data of Kovacs, Stratton and Ferry ... 

Free volume Configurational entropy Coupling model Conventional thermodynamics Statistical thermodynamics Molecular dynamics Fox et al. (1955) Di Marzio (1964) Ngai et al. (1986)... 

The exponent value of 0.6 in Jonscher regime is considered to arise by the ion-ion interactions, usually of the coulombic type. During the process of the hopping of the ions, even separate hopping events may have a broad distribution of relaxation times, and this effect can manifest as stretching of the relaxation times. Ngai s coupling model accounts for stretched exponential relaxation and considers it as a consequence of... 

It is worth noting that a secondary relaxation of intermoleeular eharacter should move towards lower frequencies as the a- relaxation does. Recent studies " indicates that it is a natural implieation of a relationship between the secondary relaxation of intermoleeular nature and the a- relaxation process. This issues can be expressed within the framework of the Coupling Model proposed by K. Ngai by using the primitive relaxation time ... 

Ngai, K. L., An extended coupling model description of the evolution of dynamics with time in supercooled liquids and ionic conductors, J. Phys. Condens. Matter, 15, S1107-S1125 (2003). 

In the coupling model of Ngai (1979), account is made for the influence of the strength of molecular relaxation on the relaxation times. It was suggested that a primary relaxing species, such as an a-relaxaticm, can be described by a time-... 

Models of structural recovery include the Kovacs-Aklonis-Hutchinson-Ramos (KAHR) model (119), Moynihan s model (120), and Ngai s coupling model (121). These models are based on work done originally by Narayanaswamy (122), incorporating the ideas of Tool (13). The models of stnictiual recovery reflect the nonlinear and nonexponential effects observed experimentally. The historical development of these equations has been detailed (7,8) only a brief description follows. The KAHR formulation (119), which is written in terms of a departure from equilibrium S rather than in terms of Tf, is conceptually easier to use when the full three-dimensional PVT surface is considered ... 

Ngai and Phillies(61) extend the Ngai-Rendell coupling model(62) to treat probe diffusion and polymer dynamics in polymer solutions. This is not an experimental paper it forces extant experimental data to confront a particular theoretical model, which in the paper was extensively reconstructed to treat the particular experimental methods under consideration. Ngai and Phillies consider zero-shear viscosities and optical probe diffusion spectra for HPC solutions, extracting from them the Ngai-Rendell model relaxation time tq and coupling exponent n. Optical probe spectra and other measurements were used to obtain n in four independent ways, namely from r](c) and from the concentration, time, and wave-vector dependences of g q,t). The four paths from t] and lead to consis-... 

Streletzky and Phillies eventually demonstrated that their results are consistent with the earlier papers of Philhes and Lacroix(63) and Ngai and Phillies(61). The demonstration consists of showing that Phillies and Lacroix had only been able to study the shorter-lived mode of probes in 300 kDa HPC, for which the Ngai-Phillies model is correct(61). In both systems, it is the shorter-lived mode that follows coupling-scaling. 

K. L. Ngai and G. D. J. Phillies. Coupling model analysis of polymer dynamics in solution probe diffusion and viscosity. J. Chem. Phys., 105 (1996), 8385-8397. 

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