Glassy systems

Up to now it has been tacitly assumed that each molecular motion can be described by a single correlation time. On the other hand, it is well-known, e.g., from dielectric and mechanical relaxation studies as well as from photon correlation spectroscopy and NMR relaxation times that in polymers one often deals with a distribution of correlation times60 65), in particular in glassy systems. Although the phenomenon as such is well established, little is known about the nature of this distribution. In particular, most techniques employed in this area do not allow a distinction of a heterogeneous distribution, where spatially separed groups move with different time constants and a homogeneous distribution, where each monomer unit shows essentially the same non-exponential relaxation. Even worse, relaxation... 

Glassy Systems A Probe for Cooperative Dynamical Length Scales. 

The glassy systems mentioned in Figs. 4.1(h) and 4.2 show that quite complex chemical compositions have been prepared in the glassy state. Up to three basic constituents are present in all ionically conducting glasses network formers, network modifiers and ionic salts, in different proportions. 

From this relationship we may expect to be proportional to the salt thermodynamic characteristics, if u+ and K -,ss have constant values at constant temperature and pressure in a given glassy system. The square root dependency of ionic conductivity on Umy has been experimentally verified over several orders of magnitude. The dissociating species is either a network modifier or a doping salt. Potentiometric (Ravaine and Souquet, 1977) or calorimetric (Reggiani, Malugani and Bernard, 1978)... 

A. Jones We would like to know whether it is a long range oscillation or whether it is a complete turning around of a series of units. There are measures of whether it is a complete rotation such as the values of NTi for different carbons. If NTi is a constant, the motion is probably rotational. In solution, I think these things tend to be rotational. As you go to bulk systems and in particular glassy systems, J. Schaefer (j. Schaefer, E. 0. Stejskal and R. Buchdahl, Macromolecules 10, (197T) ) feels... 

The main result extracted from P NMR was that the AU55 clusters do not exhibit a normal Korringa relation. Rather, there is an indication of the sort of general two-level behavior often seen in disordered glassy systems. This does not appear to be in disagreement with the results reported above, especially when one considers the modification of the intra-cluster energy levels due to the intercluster interactions. 

Sometimes R is called the fluctuation-dissipation ratio, not to be confused with the identically called but different quantity introduced in glassy systems (see Section VLB) that quantifies deviations from the fluctuation-dissipation theorem that is valid in equilibrium. 

A. Crisanti and F. Ritort, Violations of the fluctuation dissipation in glassy systems basic notions and the numerical evidence. J. Phys. A 36, R181-R290 (2003). 

The mechanism by which the self-diffusion in the relaxed state occurs is not firmly established at present. However, there are reasons to believe that for certain atoms in glassy systems, self-diffusion occurs by a direct collective mechanism and is not aided by point defects in thermal equilibrium as in the vacancy mechanism for self-diffusion in crystals (Section 8.2.1).2 These reasons include ... 

Another approach to liquid glass transition is the self-consistent phonon theory or density functional theory applied to aperiodic structures [112-114]. These theories predict the Lindemann stability criterion for the emergence of a density wave of a given symmetry. Although the finite Lindemann ratio implies a first-order phase transition, the absence of latent heat in glassy systems suggests the presence of an exponentially large number of aperiodic structures that are frozen in at Tg [94,95,110,111],... 

Equation (2.48) has been extensively tested for wide range of high-7 inorganic glasses. An important result is that the right-hand side is found to be virtually constant 4.8 0.4 for 17 inorganic glassy systems [100]. 

Sokolov and coworkers have introduced a quantity R (T) that is a measure of the relaxational to the vibrational contribution in low-frequency Raman scattering [124], If R (T) is defined as the ratio of intensity minimum to intensity maximum at the Boson peak at a temperature T, then a correlation is observed between R (Tg) and the fragility index for glassy systems such as SiC>2, GeC>2, B2O3, PS, salol, PB, PVC, and o-terphenyl [124],... 

Magnetic resonance in an assembly of ferromagnetic nanoparticles in ferrofluids, glasses and other systems has attracted much attention. But, up to now, only a few attempts have been made of quantitative, computer-simulation based analysis of SPR spectra of magnetic nanoparticles dispersed in glassy systems [2-11]. 

Another conceptual tool used in the study of glassy systems is the Walden plot [177]. Its use is based on the observation that if ions in an ionic system move independently, then the product of their viscosity and conductivity should... 

For the glass industry, temperatures at specific viscosities have traditionally been considered important markers. Figure 10.2 shows these points for various glassy systems. At... 

The general features of the D vs. Cj relations for amorphous polymer-solvent systems slightly above or below Tg° are not fully elucidated. This is mainly due to the fact that, as will be explained in the next section, the sorption processes in glassy polymers are not Fickian and hence the methods for the determination of D (cj) presented in the previous section can no longer be applied. In principle, D values of such systems could be determined from steady-state permeation measurements, but Kishimoto (unpublished) has shown that the analysis of permeation data on glassy systems is complicated by factors which are not yet fully resolved. 

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