Dynamic of polymer blends

As discussed above the self-concentration idea is able to describe one essential experimental fact of the molecular dynamics of polymer blends, the dynamic heterogeneity. But nevertheless there are some strong problems of this approach which are discussed in detail in reference Colmenero and Arbe (2007). Here only the main arguments are summarized ... 

The component dynamics in polymer-diluent mixtures discussed in the previous section are similar to those of polymer blends, such as the appearance of two different TgS (Fig. 2.15). Thus, a theory of component dynamics of polymer blends is robust only if it is also applicable to polymer-diluent mixtures and can explain the anomalous component dynamics found therein [98-101]. If it can be extended... 

Naturally, a theory of polymer-blend dynamics is less desirable if it is constructed just for explaining the local segmental dynamics of polymer blends, but has no utility for the consideration of problems related to local segmental dynamics in homopolymers. Some examples of challenging problems regarding homopolymers will be discussed in Sections 2.5 and 2.6. 

NMR Local dynamics of polymer blend chain orientation of polymer blends... 

J. (2002) Dynamics of polymer blends with intermolecular hydrogen bonding broad-... 

The combination of various fluorescence techniques, such as steady-state and time-resolved fluorescence spectroscopy and fluorescence microscopy, can provide extremely important information on the structure and dynamics of polymer blends. Many relevant examples will be presented in this chapter, with particular emphasis being placed on the most recent investigations. 

Lee et al. [21] conducted molecular dynamics simulations of the flow of a com-positionally symmetric diblock copolymer into the galleries between two siUcate sheets whose surfaces were modified by grafted surfactant chains. In these simulations they assumed that block copolymers and surfactants were represented by chains of soft spheres connected by an finitely extensible nonlinear elastic potential, non-Hookean dumbbells [22], which had been employed earlier in the simulations of the dynamics of polymer blends and block copolymers by Grest et al. [23] and Murat et al. [24]. To describe the interactions among the four components, namely the surfaces, the surfactant, and two blocks, Lee et al. [21] employed a Lennard-Jones potential having the energy parameters which are associated with the type of interactions often employed for lattice systems such as in the Flory-Huggins theory. 

This second group of tests is designed to measure the mechanical response of a substance to applied vibrational loads or strains. Both temperature and frequency can be varied, and thus contribute to the information that these tests can provide. There are a number of such tests, of which the major ones are probably the torsion pendulum and dynamic mechanical thermal analysis (DMTA). The underlying principles of these dynamic tests have been covered earlier. Such tests are used as relatively rapid methods of characterisation and evaluation of viscoelastic polymers, including the measurement of T, the study of the curing characteristics of thermosets, and the study of polymer blends and their compatibility. They can be used in essentially non-destructive modes and, unlike the majority of measurements made in non-dynamic tests, they yield data on continuous properties of polymeric materials, rather than discontinuous ones, as are any of the types of strength which are measured routinely. 

Tihe technological properties and the commercial application of several polymer blends have been studied extensively. Investigations of the basic principles, however, relating the phase structure of the blends to the properties of the individual components have not been carried out to an extent justified by the industrial value of these materials. Several methods have been used, the most successful being optical and electron microscopy and dynamic-mechanical measurements. Critical factors and difficulties in the morphological studies of polymer blends have been... 

Compared to binary mixtures of low molecular fluids, the critical behavior of polymer blends has been much less explored so far. However, a number of interesting static and dynamic critical phenomena in polymer blends attract increasing attention [4, 5], Neutron, X-ray, and static light scattering experiments belong to the major techniques for characterizing the static properties of polymer blends. Photon correlation spectroscopy (PCS) has traditionally been the method of choice for the investigation of the dynamics of critical [6-9] and noncritical [10-12] polymer blends. 

Luminescence properties of and phenomena in polymer systems continues to be widely researched in connection with mechanisms of polymer degradation and stabilization, molecular dynamics, solubility, blend miscibility, and solar energy harnessing. A number of interesting reviews have appeared. Molecular dynamics of polymers in solution and in the solid state have been covered, as has excimer formation,photoresponsive polymers,behaviour of polymer gels, and photochromic phenomena. Photoisomerization of enzymes and model compounds has also been discussed in depth, with particular emphasis on proteins and synthetic polymers containing azo-compounds or spirobenzopyrans. ... 

The n vs. n dependence is often used while discussing the dynamic data of polymer blends. Since for simple liquids the plot has the form of a semi-circular arc, deviation from a semi-circle is sometimes Identified with Immlsclbillty. However, as frequently demonstrated for homopolymers (16) and homologous polymer blends ( ) the form of the n" vs. n plot is determined by the shape of the relaxation spectrum the molecular polydlsperslty can modify the Cole-Cole plot as much as the presence of the Interphase. As a rule, the presence of (unsubtracted) yield stress appears in the plot as a sudden departure from a semi-circular pattern at higher n level. 

---