Correlated adsorption of polyelectrolytes in the “charge inversion” of colloidal particles

¹ Dipartimento di Fisica, Università di Roma “La Sapienza” Piazzale A. Moro 5, 00185 Roma, Italy
² Istituto Nazionale per la Fisica della Materia, INFM-CRS SOFT Unità di Roma 1 - Roma, Italy

Received: 10 June 2004
Accepted: 31 August 2004

Abstract

In this letter, we study the complexation of spherical colloidal particles induced by oppositely charged polyelectrolytes by means of dynamic light scattering technique. We employed cationic liposomes, 100 in diameter, and compared their aggregation behavior in the presence of differently organized counterions, i.e. simple uni-valent ions, deriving from the dissociation of salt, and multi-ions bounded to a polymer chain (large-valence polyions deriving from the ionization of two polyelectrolyte chains, polyacrylate and DNA). We show that the system behaves differently and, in the presence of oppositely charged polyions, undergoes a well-defined re-entrant condensation, following a charge inversion effect, as a function of the counterion concentration in the aqueous phase. Our results present a clear evidence of the role played by the lateral correlation of polyion chains onto the charged-particle surface, in terms of a simple Wigner crystal theory, according to the idea developed by Nguyen et al.  (Rev. Mod. Phys. 74 (2002) 329).