Dynamics, glassy polymers

Dynamics Simulation of a Glassy Polymer Melt Incoherent Scattering Function. 

Of the thermodynamic quantities just mentioned, only the determination of the expansion coefficient or other quantities reflecting its change have assumed practical importance for the identification of secondary transitions in glassy polymers. The most efficient methods for the investigation of the dynamics and intensity of molecular motions have so far been those based on the interference between molecular motion and the oscillating magnetic, electric or mechanical force field. In recent years, methods which employ various probes or labels in the study of molecular mobility have increasingly been used. 

Dynamic Mechanical Relaxations in Glassy Polymers 3.1 Dynamics of Relaxations... 

It is mostly used to describe the effect of temperature on the dynamics of relaxation processes in glassy polymers. Rearranging Eq. (8), we obtain the relation between the activation energy AU (in kJ) and the temperature of relaxation, Tr(f), detected at frequency f ... 

A method for the detailed atomistic modelling of amorphous glassy polymers has been developed [50] and applied to atactic polypropylene. This method has been described in Sect. 5.4. The quasi-static modelling of chain dynamics [51] has been described in Sect. 5.4.2. 

The results presented in Table II show that even small amounts of gas affect the cooperative main-chain molecular motions of glassy polymers. Evidence that the presence of gases in polymer cause structural and dynamic changes can be seen in the depression of the Tg (42, 43, 44), and in the increased viscoelatic relaxation rates (43, 44) of... 

The only exception to a single population of sorbent in a glassy polymer was observed in the water-cellulose acetate system (5 1, 52). In this system two resonance frequencies and two relaxation rates for water were observed. However, the two dynamic states of the water in this system are due to specific hydrogen bonding interactions rather than sorption in Langmuir type holes. 

It should be kept in mind that do and Do are really mean values, recognizing the fact that glassy polymers are heterogeneous and contain a distribution of structural and dynamic states (28). As such, these parameters are dependent on the nature of the penetrant and of the polymer (13), as well as the distribution of properties in the polymer. 

A linear relationship exists between the toughness (integrated stress-strain curve) and the dynamic mechanical dissipation factor. The types of materials that fit this relationship include glassy polymers, elastomers, and an impregnated fabric. The existence of this relationship indicates that toughness arises from the molecular motions which give rise to the dynamic mechanical properties. 

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. 

Extremely Slow Reorientation Dynamics of Moiecular Tracers in Glassy Polymers... 

Anew experimental method based on the polarization-selective photochromic reactions is proposed to monitor extremely slow reorientation dynamics of molecular tracers in glassy polymer matrix. The correlations between the local relaxation processes of polymers and the reorientation dynamics of the tracers with different sizes are found from the experimental results obtained by this method. 

Reorientation dynamics of molecular tracers in polymers is not only important for the understanding of slow relaxation phenomena in glassy polymers but plays also a critical role in practical problems such as molecular design of nonlinear optical materials with long-term stability based on dyes/polymers complexes. We show here the reorientation dynamics of molecular tracers in glassy polymers obtained by the armealing-after-irradiation method described below. These experimental results are compared to the local relaxation processes of glassy polymers obtained by the already established measurement techniques such as dielectric relaxation and solid state NMR. Finally, the molecular interpretation of the relaxation of free-volume distribution in polymers will be discussed. 

SPECIFIC EXAMPLES 4.1. Dynamics in complex glassy polymers... 

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