(475f) How Do Polyampholyte Sequences Affect the Viscosity of Salt-Added Dilute Solutions and Self-Coacervates?

We combine scaling and the random phase approximation to predict conformational behaviors of single-chain globally neutral polyampholytes (PAs) in the presence of salt, the viscosity of their dilute solutions, and the rheology of condensed self-coacervate phases. To reveal the role of the monomer sequence, PAs with Markov statistics of positive and negative charges are considered. The diagram of globular regimes of single-chain PAs is constructed and six scaling regimes are distinguished. They correspond to low/high salt concentrations and almost alternating/random correlated/highly blocky sequences of ionic monomers. As salt concentration increases, PAs of any sequence swell to the ideal-coil size, with the swelling amplitude increasing at increasing the charge clustering. In dilute solutions, this salt-induced globule-to-coil transition in single-chain PAs leads to the viscosity drop --- the so-called anti-polyelectrolyte effect --- which is shown to be stronger for highly blocky PAs.

The internal structure of the globules and macroscopic self-coacervate phases of PAs is analogous. Therefore, the obtained results can be combined with the Rouse/reputation models of polymer dynamics to predict the viscosity and relaxation time of the condensed PA phase. Their power dependencies on the salt concentration are obtained for the case of short (unentangled) and long (entangled) PA. The higher the blockiness of the opposite charges, the more viscous the self-coacervate. For any sequence, viscosity and the relaxation time decrease with the addition of salt. Our findings are important for understanding the dynamics of intracellular condensates from the point of view of polymer physics.