paper

Phase diagram of solution of oppositely charged polyelectrolytes

arXiv:cond-mat/0408153 · doi:10.1016/j.physa.2004.12.037

Abstract

We study a solution of long polyanions (PA) with shorter polycations (PC) and focus on the role of Coulomb interaction. A good example is solutions of DNA and PC which are widely studied for gene therapy. In the solution, each PA attracts many PCs to form a complex. When the ratio of total charges of PA and PC in the solution, , equals to 1, complexes are neutral and they condense in a macroscopic drop. When is far away from 1, complexes are strongly charged. The Coulomb repulsion is large and free complexes are stable. As approaches to 1, PCs attached to PA disproportionate themselves in two competing ways. One way is inter-complex disproportionation, in which PCs make some complexes neutral and therefore condensed in a macroscopic drop while other complexes become even stronger charged and stay free. The other way is intra-complex disproportionation, in which PCs make one end of a complex neutral and condensed in a small droplet while the rest of the complex forms a strongly charged tail. Thus each complex becomes a "tadpole". These two ways can also combine together to give even lower free energy. We get a phase diagram of PA-PC solution in a plane of and inverse screening radius of the monovalent salt, which includes phases or phase coexistence with both kinds of disproportionation.

29 pages, 10 figures. Major change in results and text

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