Clustering of Macroions in Solutions of Highly Asymmetric Electrolytes

Abstract

In this paper, we present results of computer simulations for a primitive model of asymmetric electrolyte solutions containing macroions, counterions and in a few cases, also co-ions. The results show that the valency of counterions plays an important role in shaping the net interaction between the macroions. For solutions with monovalent counterions, the macroions are distributed at larger distances, and in solutions with divalent counterions, the macroions come closer to each other and share a layer of counterions, whereas, in solutions with trivalent counterions, the macroions form clusters. These clusters dissolve upon dilution or addition of a simple electrolyte. These findings suggest a mechanism whereby the nonuniform distribution of macroions observed experimentally in charged systems may occur.

Electrostatic interactions in strongly coupled soft matter

“…For instance, the DNA condensation process, in which long DNA molecules condense into a tightly packed, circumferentially wound torus, is observed in experiments where multivalent counterions (such as trivalent spermidine ions) are introduced [10]. A similar trend has also been found in numerous numerical simulations of like-charged membranes, colloids and polymers [19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42], where highly charged macroions are found to form closely-packed bound states due to attractive forces of electrostatic origin. These attractive forces are of typically large strength compared to the usual van-der-Waals attraction and may have significant practical implications where, for instance, multivalent counterions are present.…”

“…We shall discuss the application of criterion (34) in Section VIII B using numerical simulations of the two-cylinder system.…”

“…Recently, there have been several simulations [28,29,30,32,33,34,35] investigating effective electrostatic attraction between like-charged spheres in the large coupling regime using multivalent counterions or in some cases, using low (29), and the coupling parameter, Eq. (32), respectively.…”

“…In particular, counterions can alter the effective interaction between like-charged macroions, and may generate a dominant electrostatic attraction between them in certain physical conditions [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,…”

“…The main scenarios which are put forward to explain the phenomenon of like-charge attraction have gone beyond the mean-field level by demonstrating that this phenomenon can be reproduced quantitatively by inclusion of electrostatic correlations [19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,…”