Thermodynamics liquid crystal polymer blends

It is the intent of this doeument to define the terms most commonly encountered in the field of polymer blends and eomposites. The scope has been limited to mixtures in which the eomponents differ in ehemical composition or molar mass or both and in which the continuous phase is polymeric. Many of the materials described by the term multiphase are two-phase systems that may show a multitude of finely dispersed phase domains. Hence, incidental thermodynamic descriptions are mainly limited to binary mixtures, although they can be and, in the scientific literature, have been generalized to multicomponent mixtures. Crystalline polymers and liquid-crystal polymers have been considered in other documents [1,2] and are not discussed here. 

Block-like and segmented polymers represent chemically bound "multicomponent" systems that, in our opinion, are able to mimic some of the non-bonded interactions occurring in blends of either compatible or not compatible pol3nners, and to describe phenomena connected with phase segregation and the onset of peculiar micromorpho-logical properties. Additionally, liquid crystal polymers, even though "monocomponent" from a macrochemical point of view in that constituted of only one polymeric material, in reality do behave, under certain selected thermodynamic conditions, as mechanical mixtures of at least two components. 

An exhaustive survey of the uses for SANS in polymer science would be too long for the space available here. Attention is focused on three aspects. Polymer blends provide an example of the application of the random-phase approximation and have also enabled a better appreciation to be obtained of the thermodynamic changes consequent on deuteration. Block copolymers in the homogeneous state are also analysable by using the random-phase approximation, and the theory of the segregation in these systems has progressed rapidly in recent years. Lastly, liquid-crystal polymers are the most recent class of polymers to be examined by SANS. They... 

In Fig. 11.3, we made a comparison between the binodals obtained from dynamic Monte Carlo simulations (data points) and from mean-field statistical thermodynamics (solid lines). First, one can see that even with zero mixing interactions B = 0, due to the contribution of Ep, the binodal curve is still located above the liquid-solid coexistence curve (dashed lines). This result implies that the phase separation of polymer blends occurs prior to the crystallization on cooUng. This is exactly the component-selective crystallizability-driven phase separation, as discussed above. Second, one can see that, far away from the liquid-solid coexistence curves (dashed lines), the simulated binodals (data points) are well consistent... 

Liquid interfaces are prevailing within the immiscible polymer blends and solutions. The effect of interfaces to polymer crystallization cannot be overlooked, not only because the practical system accumulates impurities at interfaces for heterogeneous crystal nucleation, but also because the thermodynamic conditions for crystal nucleation at interfaces are different from that in the bulk phase. The latter effect can be revealed by the theoretical phase diagrams for immiscible polymer blends, as... 

The first class of blends to be analyzed is that of a homogeneous, disordered liquid phase in equilibrium with a pure crystalline phase, or phases. If both species crystallize they do so independently of one another, i.e. co-crystallization does not occur. With these stipulations the analysis is relatively straightforward. The chemical potentials of the components in the melt are obtained from one of the standard thermodynamic expressions for polymer mixtures. Either the Flory-Huggins mixing expression (7) or one of the equation of state formulations that are available can be used.(8-16) The melting temperature-composition relations are obtained by invoking the equilibrium requirement between the melt and the pure crystalline phases. When nonequilibrium systems are analyzed, additional corrections will have to be made for the contributions of structural and morphological factors. 

Binary mixtures of a flexible polymer and a low molecular weight liquid crystalline molecule, or a rigid rod-like molecule, are of interest because of their important technological applications in high modulus fibers, nonlinear optics, and electro-optical devices. These blends are basic materials for recent new technologies of liquid crystal displays [1,2], The performances of these systems are closely related to phase separations and conformations of polymer chains dissolved in a liquid crystalline phase. One of the main problems is to examine the location of various phases such as isotropic, nematic, and smectic phases, depending on temperature and concentration. To understand the thermodynamics and thermal instability of these blends, it is important to consider the co-occurrences between liquid crystalline ordering and phase separations. 

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