Relaxation mechanisms, polymer glass

M.L. Williams, R.E. Landel, and J.D. Ferry, The temperature dependence of relaxation mechanisms in amorphous polymers and other glass-forming Uquids, J. Am. Chem. Soc., 77, 3701-3707, 1955. 

M. L. Williams, R.R Landel, and J.D. Ferry The Temperature Dependence of Relaxation Mechanisms in Amorphous Polymers and Other Glass-Forming Liquids. ... 

The dynamic mechanical thermal analyzer (DMTA) is an important tool for studying the structure-property relationships in polymer nanocomposites. DMTA essentially probes the relaxations in polymers, thereby providing a method to understand the mechanical behavior and the molecular structure of these materials under various conditions of stress and temperature. The dynamics of polymer chain relaxation or molecular mobility of polymer main chains and side chains is one of the factors that determine the viscoelastic properties of polymeric macromolecules. The temperature dependence of molecular mobility is characterized by different transitions in which a certain mode of chain motion occurs. A reduction of the tan 8 peak height, a shift of the peak position to higher temperatures, an extra hump or peak in the tan 8 curve above the glass transition temperature (Tg), and a relatively high value of the storage modulus often are reported in support of the dispersion process of the layered silicate. 

In Sec. IV we discuss another TPM dye, malachite green (MG), which was used as a molecular probe for glass transition of alcohols and polymers [11,12], Analysis of the temperature dependence of nonradiative relaxation in MG shed light on the understanding of the mechanism of glass transition. Novel experimental observations are divided into two classes. (1) The critical temperature (Tc) predicted by the mode-coupling theory (MCT) was undoubtedly... 

Below Tg, structural relaxation is too slow to be observable, but secondary processes persist, which determine, e.g., the mechanical and dielectric properties of glasses. These processes have been extensively studied for polymers, where they are usually associated with polymer-specific dynamics such as side-group motion. From the point of view of glass physics, it is more interesting to investigate secondary relaxation processes in glasses comprised of rigid molecules, i.e., molecules without... 

This paper has reviewed several studies, particularly those performed on the phosphate polymers, in which ionic forces were imjx>rtant in determining the properties or behavior of the material. Only very few properties were investigate among these were 1) the glass transitions as a function of the molecular we ht, the nature of the terminal group, and the nature of the counterion, 2) the viscoelastic properties as a function of the counterion and 3) the viscoelastic relaxation mechanism, with specific emphasis on the separation of the a and mechanisms. In this treatment, a deliberate attempt was made to present pertinent theories, insofar as they exist, but it seems evident that here as much work remains to be done as on the experimental level, if not more. 

Fluorescence studies of excimer formation in the probe give information regarding the microviscosity of the matrix. Unusually the probe seems to reflect the low frequency glass transition and caution must be applied in interpreting photophysical data obtained with such probes in terms of polymer relaxation mechanisms. 

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