Eur. Phys. J. E 4, 143-152
Flexible linear polyelectrolytes in multivalent salt solutions: Solubility conditions
F.J. Solis and M. Olvera de la CruzNorthwestern University, Department of Materials Science and Engineering, Evanston, IL 60208, USA f-solis@northwestern.edu
m-olvera@northwestern.edu
monica@stimpy.ms.nwu.edu
(Received 15 May 2000 and Received in final form 28 June 2000)
Abstract
Single- and double-stranded DNA and many biological and
synthetic polyelectrolytes undergo two structural transitions upon
increasing the concentration of multivalent salt or molecules.
First, the expanded-stretched chains in low monovalent salt
solutions collapse into nearly neutral compact structures when
the density of multivalent salt approaches that of the monomers.
With further addition of multivalent salt the chains redissolve
acquiring expanded-coiled conformations. We study the
redissolution transition using a two-state model (F.J. Solis, M.
Olvera de la Cruz, J. Chem. Phys. 112, 2030 (2000)). The
redissolution occurs when there is a high degree of screening of
the electrostatic interactions between monomers, thus reducing
the energy of the expanded state. The transition is determined by
the chemical potential of the multivalent ions in the solution,
and the inverse screening length, 
. The transition
point also depends on the charge distribution along the chain but
is nearly independent of the molecular weight and degree of
flexibility of the polyelectrolytes. We generate a diagram of
versus
where we find two regions of
expanded conformations, one with charged chains and the other with
overcharged (inverted charge) chains, separated by a collapsed
nearly neutral conformation region. The collapse and
redissolution transitions occur when the trajectory of the
properties of the salt crosses the boundaries between these
regions. We find that in most cases the redissolution occurs
within the same expanded branch from which the chain
precipitates.
61.20.Qg - Structure of associated liquids: electrolytes, molten salts, etc..
61.25.Hq - Macromolecular and polymer solutions; polymer melts; swelling.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001
