Polymers molecular relaxation processes studied

The molecular relaxation process has been studied by the autocorrelation function of normal modes for a linear polymer chain [177]. The relaxation spectrum can be analyzed by the Kohlrausch-Williams-Watts function [177,178] ... 

The TSC spectra of polymers have several peaks associated with structural transitions, even though the current is typically of the order of picoamperes. On this account, TSC is a powerful and sensitive method for polymer analysis. In the last 25 years, TSC analysis has been applied to the study of molecular relaxation processes in polymers, including copolymers, polymer blends and, composite materials [43-46]. TSC of polymers is also sensitive to additives, dopants, plasticizers, water and low molecular weight organics. 

Dynamic mechanical (DMA) and dielectric analysis (DEA) methods are used both to study molecular relaxation processes in polymers and to determine inherent... 

Tt is sometimes a healthy attitude for one to consider whether impurity fluorescence in a sample can itself be used as an intrinsic sensor of molecular events within the polymer, and whe ther parasitic-quenching might not provide a useful means of studying molecular relaxation processes which control impurity (oxygen) diffusion. There are numerous reports in the literature of how such studies of emission quenching can provide interesting information relevant to mechanical relaxation processes in polymers (8). 

As noted in the introductory section, our purpose is to use the excimer fluorescence technique to study the flexibility of various pol3nner chains in polymer matrices. One question which arises is to know if the probe undergoes a conformational change via a free-volume dependent molecular relaxation process related to the glass transition of the polymer matrix. The free volume of a polymer at a given temperature should qualitatively relate to its Tg value. 

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. 

The effect of diluents on the viscoelastic behavior of amorphous polymers is more complex at temperatures below T, i.e., in the range of secondary relaxation processes. Mechanical, dielectric and NMR measurements have been performed to study the molecular mobility of polymer-diluent systems in this temperature range (see e.g. From extensive studies on polymers such as polycarbonate, polysulfone and polyvinylchloride, it is well known that diluents may suppress secondary relaxation processes. Because of the resulting increase in stiffness, these diluents are called antiplasticizers . Jackson and Caldwell have discussed characteristic properties... 

Because chromophores orientation is important for creating anisotropy and optical nonlinearities, intensive studies have been performed to understand induced molecular orientation and relaxation processes in polymers. To gain further insight into the physics of thin polymer films and the effects of molecular orientation in solid polymers, studies at high pressure could be beneficial. Pressure as a thermodynamic parameter is widely used to study... 

In amorphous state, solid polymers retain the disorder characteristic for liquids, except that the molecular movement in amorphous solid state is restrained. The movement of one molecule versus the other is absent, and some typical liquid properties such as flow are absent. At low stress, polymers display elastic properties, reverting to a certain extent to the initial shape in a relaxation process. However, they can be irreversibly deformed upon application of appropriate force. The deformation and flow of polymers is very important for practical purposes and is studied by a branch of science known as rheology (see e.g. [1]). The combination of mechanical force and increased temperature are commonly applied for polymer molding for their practical applications. The polymers that can be made to soften and take a desired shape by the application of heat and pressure are known as thermoplasts, and most linear polymers have thermoplastic properties. 

The main finding of the present study is the discovery of a novel relaxation process in thin films of cis-1,4-polyisoprene, called a confinement-induced mode, attributed to fluctuations of terminal subchains formed by the immobilization of the polymer segments at one of the two confining interfaces. In the context of our molecular model and with the help of the simulations, one can understand most of the features observed in the experiment ... 

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