Phase Behavior of AqueousWayne

The phase behavior of aqueous mixtures of gelatin and oligosaccharides above their gelation temperature is investigated experimentally, and rationalized according to a simple multicomponent Flory–Huggins model. When the gelatin is only weakly charged, entropic considerations dominate and it is found that the cloud point curve of the mixtures is extremely sensitive to the molecular weight distribution of the oligosaccharide. Even very small quantities of long-chain oligosaccharides present in an otherwise short-chain oligosaccharide population can radically reduce the compatibility. Added salt does not significantly affect the phase diagram, although a strong effect on the kinetics of phase separation is seen. Lowering the pH increases the electrostatic charge on the gelatin and strongly enhances the compatibility. Because the kinetics of gelation and phase separation are different, gelation can freeze in nonequilibrium states. Therefore, all phase diagrams were determined well above the gelation temperature (about 377C). q 1997 John Wiley & Sons, Inc. Biopoly 41: 607–622, 1997