Effect of Polymer Net Charge on Polyampholyte-Polyanion Coacervate Complexation

Polymer coacervate complexes are commonly formed upon the liquid-liquid separation of the mixture of oppositely charged polyelectrolytes in salted aqueous solution. Recently we have demonstrated that biphasic coacervate complexes and monophasic gel-like complexes can be also formed between net neutral polyzwitterions and inorganic polyoxometalate (POM) polyanions in salted solutions. To further understand the binding between polyzwitterion and polyanion and the resulting structures of dense coacervate complexes, we examine the effect of net charge of polyampholytes on the phase behavior of polyampholyte-POM mixtures in LiCl aqueous solution. By tuning the net charge of polyampholytes from being 10% positively charged to 10% negatively charged, the coacervate complex phase is much narrowed. Moreover, the gel-like complex formation is suppressed in the mixture of net negatively charged polyampholyte and POM polyanions in LiCl solutions. Linear rheological characterization of polyampholyte-POM complexes shows that the measured shear moduli of dense coacervate complexes strongly depend on the net charge of polyampholyte, leading to the presence of an optimal polyampholyte-to-POM charge ratio for the maximal viscoelasticity.