Polymer-solvent ternary systems behavior

Fifty-six isothermal data sets for vapor-liquid equilibria (VLB) have been used for 15 polymer-HSolvent binaries, 11 copolymer-nsolvent binaries and for 30 polymer-polymer-solvent ternaries to study compatibility of polymer blends. The equilibrium solubility of a penetrant in a polymer depends on their mutual compatibility. Equations based on theories of polymer solution tend to be more successful when there is some kind of similarity between the penetrant and the monomer repeat unit in the polymer, e.g., for nonpolar penetrants in polymers which do not contain appreciable polar groups. Expected nonideal behavior has been observed for systems containing hydrocarbons and poly(acrylonitrile-co-butadiene). The role of intramolecular interaction in vapor-liquid equilibria of copolymer-nsolvent systems is well documented for poly(aciylonitrile-co-butadiene) that have higher affinity for acetonitrile than do polyaciylonitrile or polybutadiene. 

A ternary system consisting of two polymer species of the same kind having different molecular weights and a solvent is the simplest case of polydisperse polymer solutions. Therefore, it is a prototype for investigating polydispersity effects on polymer solution properties. In 1978, Abe and Flory [74] studied theoretically the phase behavior in ternary solutions of rodlike polymers using the Flory lattice theory [3], Subsequently, ternary phase diagrams have been measured for several stiff-chain polymer solution systems, and work [6,17] has been done to improve the Abe-Flory theory. 

These phase diagrams were assessed accurately in preliminary studies, since the phase separation method is based on the precipitation of a shell material from the phase behavior of the ternary system. Actually, the core material served as a poor solvent for the shell polymer. During evaporation of the solvent, a precipitation of the shell polymer on the surface of core droplets occurs. 

The PEG/water, PPG/water, and PVAL/water are among the most extensively studied water-soluble polymer solutions. These systems typically show a closed-loop phase behavior (Figure 16.4). Results for some ternary systems have been reported many of these data are for PEG/Dextran/water and PEG/water/salts and related systems, which are important for separating biomolecules such as proteins. Only few data for PEG or other hydrogen bonding polymer with mixed water solvents have been reported. 

To explain the behavior of a polymeric multicomponent system, the polymer is considered as a mixture of two polymer species, PI and P2. By doing this, the polymer-solvent system can be illustrated using a ternary Gibbs triangular diagram. It is assumed that one species of the polymer, PI, has a lower molecular mass than P2 and is completely miscible with the solvent, whereas P2 exhibits an immiscibility region (Figure 15.5). 

Another example of the phase behavior of asymmetric molecules is given in Fig. 3.22 for aqueous solutions of hydroxypropyl cellulose.(97) The phase diagram for this system shows all of the major features expected from the Rory theory for an asymmetric polymer solute. The slight tilting of the narrow biphasic region could possibly be attributed to some molecular flexibility as well as anisotropic interac-tion.(98) The phase diagram for the ternary system, polymer and two solvents, for poly(p-phenylene terephthalamide) also shows the major features expected from theory. (99)... 

Qualitatively correct and occasionally also quantitatively satisfactory representation of LLE for binary and ternary polymer-solvent systems is achieved, especially for the UCST-type phase behavior. A single investigation for SLLE also shows good results. 

Most work has been concentrated on the formation, structure and properties of ternary systems composed of one cellulose derivative and mixed solvents or other polymer blended solutions. Thus, the liquid crystal properties of ethylcellulose/acrylic acid, ethylcellulose/dichloroacetic acid and ethylcellulose/glacial acetic acid solutions were studied, observing the mesophase behavior when their concentrations exceeded 0.6, 0.3, and 0.35 g/ml, respectively, at room temperature [143]. Also,... 

This section deals with the phase-separation behavior of ternary systems, where a distinction is made between polymer solutions in mixed solvents (Sect. 4.2.1) and solutions of two polymers in a single solvent (Sect. 4.2.2). Furthermore, the systems are classified according to the way the thermodynamic properties of the ternary systems are made up from the properties of the corresponding binary subsystems Simplicity denotes smooth changes in the phase behavior of the binary subsystems upon the addition of the third component in its pure form or in mixtures (see later). Cosolvency means that the thermodynamic quality of mixture of two components is higher with respect to the third component than expected by simple additivity, i.e., cosolvency reduces the extension of the two-phase region with respect to that expected from additivity. Cononsolvency, finally, denotes the opposite behavior, i.e., an extensimi of the two-phase region beyond expectation. 

An important point here is that according to the theory of critical phenomena, the critical exponents take universal values essentially independent of the microscopic details of the system. The natural question then is whether the exponents characterizing the curve, the radiation scattering intensity, the correlation length, and the interfacial tension behavior in polymer-polymer-solvent systems are the same as for ternary mixtures of small molecules. It is also essential to study how the critical amplitudes depend on the molecular weight of chains. 

Figure 7.6 illustrates a ternary phase diagram for a polymer-polymer-common solvent system. Sketch qualitatively a ternary phase diagram for a polymer-solvent-non-solvent system. Include tie lines and illustrate the effects of temperature and polymer molecular weight on two additional diagrams. Assume that the solvent and nonsolvent are soluble in all proportions, and that the polymer has UCST behavior. 

This work discusses new models and techniques for Improving our understanding and description of phase behavior in aqueous/polymer systems. We have considered only some of the potentially important classes of aqueous/polymer systems this work provides a framework on which to base further studies in this area. Important classes of hydrogels not considered here are pH-sensitive gels [4, 38], and gels in mixed-solvent solutions [4], A satisfactory theoretical description has not yet been obtained for the large volume transitions observed In these systems. It Is likely that volume transitions induced by changing solvent composition (i.e., acetone/water ratio) may be explained by the oriented-lattice framework extended to ternary systems. 

This section deals with two component systems only. It excludes uncommon polymers and solvents. An overview concerning the typical behavior of ternary systems is presented in the theoretical section. 

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