Equilibrium phases of polyelectrolytes in ionic solutions

Abstract

Polyelectrolytes are the charged polymers in ionic solutions, such as microtubules, filamentous actins, and DNA. Polyelectrolytes are highly charged but they can form the condensed phases in equilibrium, which means the can attract each other overcoming the electrostatic repulsion. It is our ultimate goal to understand the like-charge attraction. A clue of this question is the presence of oppositely charged mobile ions, namely \textit{counterions} dissolved from polyelectrolytes in ionic solutions. Counterions are expected to screen the bare repulsion of polyelectrolytes, so the distribution of counterions near polyelectrolytes can affect the interaction between polyelectrolytes and then understating on the counterion distribution is the first step to figure out the like-charge attraction. The examples of counterions are spermidine and spermine known as the effective agents for DNA condensation. They are multivalent ions and have extended rodlike structure with well-separated charge distributions along the backbone. Under the observation, we suppose that the valence and the internal structure of counteirons can play a crucial role in the interaction between polyelectrolytes. Thus, we conduct the research on the equilibrium phases of polyelectrolytes in ionic solutions with respect to the electrostatic strength and the internal structure of counterions. Furthermore, we take the presence of salt ions into account when examining the like-charge attraction in order to consider the physiological situation surrounded by counterions as well as salt ions from the electrolyte solution.