Relaxation rate, dynamic behavior

The effect of oxidative irradiation on mechanical properties on the foams of E-plastomers has been investigated. In this study, stress relaxation and dynamic rheological experiments are used to probe the effects of oxidative irradiation on the stmcture and final properties of these polymeric foams. Experiments conducted on irradiated E-plastomer (octene comonomer) foams of two different densities reveal significantly different behavior. Gamma irradiation of the lighter foam causes stmctural degradation due to chain scission reactions. This is manifested in faster stress-relaxation rates and lower values of elastic modulus and gel fraction in the irradiated samples. The incorporation of O2 into the polymer backbone, verified by IR analysis, conftrms the hypothesis of... 

Fig. 7. Characteristic relaxation rate for the Rouse relaxation in polyisoprene as a function of momentum transfer. The insert shows the scaling behavior of the dynamic structure factor as a function of the Rouse variable. The different symbols correspond to different Q-values. (Reprinted with permission from [39]. Copyright 1992 American Chemical Society, Washington)...

Steady-state behavior and lifetime dynamics can be expected to be different because molecular rotors normally exhibit multiexponential decay dynamics, and the quantum yield that determines steady-state intensity reflects the average decay. Vogel and Rettig [73] found decay dynamics of triphenylamine molecular rotors that fitted a double-exponential model and explained the two different decay times by contributions from Stokes diffusion and free volume diffusion where the orientational relaxation rate kOI is determined by two Arrhenius-type terms ... 

The dynamic behavior of HM-HEC monolayers depends on the concentration in bulk solution (10, 11, 12) the monolayer obtained from dilute solution, having a higher relaxation rate constant, is more flexible and presumably thinner (Experiments Numbers 1 and 3). 

This diffusion constant can be measured by dynamic light scattering. Tanaka and Filmore originally considered the case K P fi, for which swelling occurs from the boundary with the relaxation rate n2D/R2 and the thickness of the diffusion layer is (Df)1/2 after a change of the boundary condition at t = 0. However, this normal diffusion behavior is altered for swelling near the point K = 0. 

Very few experiments have been performed on vibrational dynamics in supercritical fluids (47). A few spectral line experiments, both Raman and infrared, have been conducted (48-58). While some studies show nothing unique occurring near the critical point (48,51,53), other work finds anomalous behavior, such as significant line broadening in the vicinity of the critical point (52,54-60). Troe and coworkers examined the excited electronic state vibrational relaxation of azulene in supercritical ethane and propane (61-64). Relaxation rates of azulene in propane along a near-critical isotherm show the three-region dependence on density, as does the shift in the electronic absorption frequency. Their relaxation experiments in supercritical carbon dioxide, xenon, and ethane were done farther from the critical point, and the three-region behavior was not observed. The measured density dependence of vibrational relaxation in these fluids was... 

Simulations of solvation dynamics following charge transfer at the water liquid/vapor interface[53,80] have shown that the solvent relaxation rate is quite close to that in bulk water, even though one might expect (based on the reduced interfacial dielectric constant and simple continuum model arguments) to have a significantly slower relaxation rate. The reason for this behavior is that the interface is deformed and the ion is able to keep its first solvation shell nearly intact. Since a major part of the solvation dynamics is due to the reorientation of first shell solvent dipoles, the rate relative to the bulk is not altered by much. 

A solute distribution exists in the melt because the solidification is carried out at a finite rate. For example, if k0 < 1, then solute is rejected and accumulates at the surface which is solidifying, and this creates solute gradients in the melt which tend to be relaxed by molecular diffusion and any convection which may exist. The interfacial distribution coefficient, k, refers to the solid to liquid solute concentration ratio at the interface. It is k which is used in transport calculations when one is trying to understand the dynamic behavior of zone refining systems. It usually is found that equilibrium exists locally at the solid-liquid interface, in which case k ko. 

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