Fantastic Viscoelastic Saloplastic*

Spontaneous liquid-liquid phase separation, into a polyelectrolyte complex, occurs when aqueous solutions of oppositely-charged polyelectrolytes are mixed. In the absence of salt, stoichiometric mixtures of these polyelectrolyte complexes contain well-paired repeat units Pol⁺ and Pol^-. Salt water “dopes” and plasticizes the complex, yielding a broad set of materials properties from glassy to rubbery to viscous fluid to single-phase solutions. This “saloplasticity” is reversed by rinsing the complex in water to extract the salt. This talk will illustrate the concept of saloplasticity and will show how the “sticky associations” between Pol⁺ and Pol^-, which control the viscoelastic behavior of complexes, may be reversibly regulated with salt. An unusual scaling of viscosity, η, with molecular weight, M is observed in the sticky reptation regime: η ~ M⁵ .