Eur. Phys. J. E (2004) 15: 465-472
https://doi.org/10.1140/epje/i2004-10079-y

Spherical polyelectrolyte block copolymer micelles: Structural change in presence of monovalent salt

¹ Service de Physique de l’Etat Condensé, CEA-Saclay, DRECAM, F-91191, Gif-sur-Yvette Cedex, France
² Laboratoire Interdisciplinaire sur l’Organisation Nanométrique et Supramoléculaire (LIONS), Service de Chimie Moléculaire, CEA-Saclay, DRECAM, F-91191, Gif-sur-Yvette Cedex, France
³ Institut Laue-Langevin, B.P. 156, F-38042, Grenoble Cedex, France
⁴ Laboratoire Léon Brillouin, CEA-Saclay, DRECAM, F-91191, Gif-sur-Yvette Cedex, France
⁵ Waters Corporation, 34 Maple Street, 01757-3696, Milford, MA, USA
⁶ Chemical Sciences Division, Oak Ridge National Laboratory, Department of Chemistry, University of Tennessee, 552 Buehler Hall, 37996-1600, Knoxville, TN, USA

^* e-mail: guenoun@drecam.saclay.cea.fr

Received: 8 January 2004
Accepted: 27 October 2004
Published online: 15 December 2004

Abstract

Spherical polyelectrolyte block copolymer micelles were investigated as a function of added NaCl salt concentration using Small-Angle Neutron Scattering (SANS) and Light Scattering (LS). The micelles are formed by the self-association of charged-neutral copolymers made of a long deuterated polyelectrolyte moiety (NaPSS_d)₂₅₁ and a short hydrophobic moiety (PEP)₅₂. In presence of salt, the core shape and the aggregation number of the micelles are not affected. The hydrodynamic radius of the micelle is found to be identical to the radius of the whole micelle deduced from neutron scattering and thus the hydrodynamic radius is a valid measure of the corona thickness. At the lowest salt concentrations investigated the thickness of the corona, R _s, remains essentially constant and a contraction is observed above an added-salt concentration c _s of 2×10^-2 M where this crossover concentration corresponds to the average ionic strength of the free counterions in the corona. The contraction takes place while maintaining a rod-like behavior of the chains at short scale and obeys to: R _s ∼ c _s ^-0.18. The exponent 0.18 suggests an electrostatic persistence length proportional to the Debye screening length.