ABSTRACT
References .......................................................................................................................... 620
Two types of phase separation are typical of mixed aqueous solutions of dissimilar macro-
molecules. Phase separation is caused either by thermodynamic incompatibility of biopoly-
mers or the formation of insoluble interbiopolymer complexes [1-12]. These types of phase
separation are also referred to as simple and complex coacervations or segregative and
associative phase separations, respectively. Figure 17.1 schematically illustrates the difference
between these phase separation processes. They are methodologically distinguished by ana-
lyzing the composition of the coexisting phases [12-17]. Biopolymer incompatibility results in
a state in which the biopolymers are mainly in different phases while interbiopolymer com-
plexing leads to the concentration of the biopolymers in the same phase, normally, the bottom
phase. Attraction between different macromolecules usually leads to interpolymer complexes,
which can be either soluble or insoluble. Repulsion between different macromolecules results
from the fact that macromolecules tend to be surrounded by molecules of their own type.
Incompatible macromolecules, macromolecular associates, and soluble complexes form sep-
arated phases when the bulk biopolymer concentration exceeds a certain critical level. The
latter decreases with an increase in particle size, for example, from macromolecules to
colloidal polymer particles [17-21]. This difference corresponds to the transition from phase
separation caused by biopolymer incompatibility to depletion flocculation [13,17].
