Rheological properties of O-carboxymethyl chitosan – gum Arabic coacervates as a function of coacervation pH

The rheological properties of O-carboxymethyl chitosan (O-CMC) – gum Arabic (GA) coacervates varied greatly with the coacervation pH. At pH 3.0, the coacervate displayed the flow induced shear thickening property in shear rates below 100 s−1 and then behaved as a Newtonian fluid hereafter; at pH 4.5, the coacervate exhibited the characteristic shear thinning property of a pseudoplastic fluid; while at pH 6.0, the coacervate occurred as a Bingham fluid. The highest viscosity and modulus values of the coacervates were recorded not in the pH value with maximum electrostatic interaction. Zeta potential analysis revealed that the high proportion of O-CMC in the coacervates possibly contributed to the unique rheological properties of the coacervates. SEM observation imaged a layer-by-layer structure for the coacervates prepared at pH 3.0, 4.5, and 6.0. It was concluded that the composition of the O-CMC – GA coacervates greatly influenced their rheological properties and the desired property can be obtained by varying the coacervation pH.