Collapse dynamics of a polyelectrolyte

¹ Department of Physics, Sejong University - Seoul, South Korea, 143-747
² Max-Planck Institut für Polymerforschung - P.O. Box 3148, 55128 Mainz, Germany
³ Institut Charles Sadron - 67083 Strasbourg Cedex, France
⁴ Department of Physics, University of Florida - Gainesville, FL 32611, USA

Received: 14 October 2003
Accepted: 26 February 2004

Abstract

We study the collapse dynamics of a polyelectrolyte (PE) chain upon the change of solvent condition induced by a change of pH or solvent quality. The kinetics of a PE collapse differs from that of a neutral polymer because its initial conformation is naturally stretched due to the repulsive electrostatic interactions. If the solvent change leads to a complete neutralization of charge, the final configuration is one spherical globule (pearl). The chain conformation goes through an intermediate collinear conformation of pearls connected with strings. The dynamics is controlled by the motion of the two terminal pearls growing at the expense of small pearls in between. A slow coarse graining of other pearls in the middle does not affect the large-scale dynamics. The estimated total time for the collapse is . In the case when the polymer remains charged after the change of solvent, the final structure is a stretched string of pearls. The collapse is a two-stage process: 1) relaxation to the stretched structure of pearls which are 2/5 of the equilibrium size, with a characteristic time and 2) equilibration of pearl size and number, which requires activation to overcome energy barriers. The estimated activation energy barrier favorably agrees with the computer simulations by Limbach et al.  (Europhys. Lett.60 (2002) 566).