Beyond pure, single-component systems

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. 

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