title: A cell-model study on counterion fluctuations in macroionic systems: effect of non-extensiveness in entropy.
abstract: Rigorously speaking, entropy is slightly non-extensive, and this non-extensiveness, which characterizes the degree of fluctuations, can contribute to effective interactions between mesoscopic objects. In this paper, we consider a pair of macroions, each accompanied by 1000 counterions, and with a cell-model description we demonstrate that the slow variation of non-extensiveness in counterion entropy over macroionic distance leads to an effective long-range attraction between the macroions. With the aid of Monte Carlo simulation and a Bragg-Williams theory including counterion number fluctuations, we find the depth of attraction in free energy to be approximately 0.2k(B)T. The observation in our cell-model study provides an insight for further understanding of effective interactions in real macroionic systems.
authors.affiliation: Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan.
authors.forename: Yiing-Rei
authors.initials: YR
authors.lastname: Chen
authors.forename: Chi-Lun
authors.initials: CL
authors.lastname: Lee