Phase diagram of the system sodium alginate/water: a model for biofilms.

Sodium alginate is a polyelectrolyte consisting of the monomer units beta-D-mannuronate and alpha-L-guluronate. Mainly based on the theory of Khokhlow et al., the state diagram of the binary system alginate/water has been calculated using different sets of parameters like degree of ionization, degree of polymerization and interaction function. The calculations comprise miscibility gaps, liquidus curves, eutectic points and the behaviour at temperatures below the melting point of water. Also gel and swelling curves have been treated, where gels are physically crosslinked. The DSC diagram of a 0.5 by wt.% polymer sol shows a double melting peak, which is explained by a heterogeneity above 0 degrees C. The crystallization of water seems to concentrate the gelled system irreversibly.