Complexes of the weak and semi-flexible biopolyelectrolytes, chitosan (CH) and hyaluronic acid (HA), phase separate as coacervates, precipitates or flocs. Turbidimetric titrations and light microscopy show that the state of the dense phase depends on the molar ratio of HA carboxyl:CH amines, and is strongly dependent on the respective degrees of ionization a andb. Due to the strong charge complementarity between HA and CH, phase separation takes place at very acidic pH (a ~ 0.1) and the onset of phase separation (pHj) is suppressed at higher salt concentrations; i.e. I > 0.75 M NaCl. At fixed pH and total polymer concentration, the ionic strength dependence of the turbidity is non-monotonic.  The critical ionic strength was observed regardless of the pH of the medium.  Chain length and charge density (degrees of deacetylation of chitosan) had a direct relationship with pHj. Highest turbidity was observed for non-stoichiometric complexes.  All systems display a discontinuity in the ionic strength dependence of the turbidity, corresponding to a transition from aggregate formation to aggregate dissolution. Taking this ionic strength Icrit as a measure of the resistance to salt-induced disaggregation, it is notable that it achieves a maximum value when b is maximum.

Phase separation between semiflexible biopolyelectrolytes

248th National Meeting (2014)

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