2003/07/31 by R. Zhang, B. I. Shklovskii, B. I. Shklovskiǐ
Biochemistry, Genetics and Molecular Biology · Chemistry · Materials Science · Physics and Astronomy · #DNA and Nucleic Acid Chemistry #Electrostatics and Colloid Interactions #Material Dynamics and Properties #cond-mat.soft
paper · pdf · doi:10.1103/physreve.69.021909
published as Phys. Rev. E69, 021909 (2004). · 10 pages, 9 figures. The text is rewritten, but results are not changed
arxiv created 2003/11/26 · openalex publication_date 2004/02/26 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Aggregation of two oppositely charged colloids in salty water is studied. We focus on the role of Coulomb interaction in strongly asymmetric systems in which the charge and size of one colloid is much larger than the other one. In the solution, each large colloid (macroion) attracts a certain number of oppositely charged small colloids (Z-ion) to form a complex. If the concentration ratio of the two colloids is such that complexes are not strongly charged, they condense in a macroscopic aggregate. As a result, the phase diagram in a plane of concentrations of two colloids consists of an aggregation domain sandwiched between two domains of stable solutions of complexes. The aggregation domain has a central part of total aggregation and two wings corresponding to partial aggregation. A quantitative theory of the phase diagram in the presence of monovalent salt is developed. It is shown that as the Debye-Hückel screening radius r(s) decreases, the aggregation domain grows, but the relative size of the partial aggregation domains becomes much smaller. As an important application of the theory, we consider solutions of long double-helix DNA with strongly charged positive spheres (artificial chromatin). We also consider implications of our theory for in vitro experiments with the natural chromatin. Finally, the effect of different shapes of macroions on the phase diagram is discussed.