Rigid-chain polymer-solvent system

Phase Equilibrium in a Rigid-Chain Polymer-Solvent System.81... 

Fig. 9. A hypothetical phase diagrams for a rigid-chain polymer-solvent system in a wide temperature range...

Fig. 12. Schematic phase diagram for a rigid-chain polymer-solvent system involving the formation of the liquid crystalline phase and crystallosolvate (according to...

Phase equilibrium in a rigid-chain polymer-solvent system may be considerably affected by various factors. In particular, this applies to... 

Figure 3. Phase equilibria in a "rigid-chain-polymer-solvent" system with formation of a liquid-crystalline phase.

It would thus be fcwmally possible to assign the described system, which contains a liquid-crystalline phase, to lyotropic liquid crystals. Actually, this system differs fiom true lyotropic liquid-crystalline systems with respect to the mechanism of the onset of the ordoed state since only a decrease in the temperature of the C-LC transition is involved in the rigid-chain polymer-solvent system due to addition of the solvent, and in this sense, the system does not differ from thomotropic liquid-crystalline systems formed in the pure polym with an increase in the temperature. In addition, let us examine the behavior of a system with a fixed concentration of solvent cwresponding to a composition of the system V2 (ho% and below, subscripts 1 and 2 in the volume and weight compositimis of the system refer to the solvent and polymer, respectively). An increase in the temperature to Tj results in the complete transition of the system into the liquid-crystalline state, which corresponds to the usual thermotropic transition, and the solvent does not play any specific role here except for decreasing the melting point of the crystalline phase. With a further increase in the tempaature, the same ttansitions LC -> LC +1 (at and LC +1 -> I (at as in ordinary thermotropic liquid-crystalline systems take place. 

Fig. 2.5. Theoretical phase equilibrium diagram in V2 % coordinates for the rigid-chain polymer-solvent system (according to Floiy [18]) with x = 1(X) (I isotropic. A anisotropic phases).

Fig. 2.17. Generalized phase diagram for the rigid-chain polymer-solvent system with separation of the crystal solvate (CS), liquid-crystalline phase (LC), and crystalline polymer (CP).

Fig. 2.22. Mutual position of equilibria in the rigid-chain polymer-solvent system [57] 1) phase diagram with formation of the...

Precipitation of the polymer on addition of a nonsolvent or with any changes in the thermodynamic parameters in solutions whose conc tration is below the critical point of the transition to the liquid-crystalline state is the most typical case of the intermediate phase equilibrium in rigid-chain polymer-solvent systems. Instead of the anticipated establishment of isotropic-anisotrqric phase equilibrium, equilibrium of two amorphous (isotropic) phases initially arises if the parameter x attains values greater than +0.5. 

One of the specific features of these polymer systems is a low mobility of the macromolecules and correspondingly slow phase transition rates. This enables one to use, in analyzing such systems, composite phase diagrams showing all the types of phase equilibria inherent in a given system. Extension of this principle to the systems "rigid-chain- polymer-solvent" makes it possible to construct a phase diagram which combines (a) equilibrium with the formation of a crystalline phase, (b) equilibrium with the formation of liquid-crystalline phases, and (c) equilibrium with the formation of amorphous (liquid) phases. 

The main objective pursued in this case is to analyze the phase transitions occurring in real systems "rigid-chain polymer-solvent" with an allowance for the kinetics of these transitions. 

The higher the equilibrium chain rigidity and the increment of refractive index dn/dc in the polymer-solvent system, the more pronounced is this effect. For a rigid-chain polymer the Aa value in Eq. (49) is calculated according to )... 

The phase equilibrium in systems containing rigid-chain polymers is characterized by the formation of a liquid-crystalline state, which fact can be illustrated by the diagram due to Flory reproduced in Figure 3. At x values below 0,the polymer-solvent system forms either an isotropic (one-phase) solution mixture of... 

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