Abstract
By means of Langevin dynamics simultion,we investigated the properties of a flexible polyelectrolyte (PE) at different salt concentration in external electric fields. The radius of gyration (Rg) and end-to-end distance (Re) alter with the strength of electric field. At weak electric field, the values of Rg and Re are roughly constant. The field does not affect PE behavior. Further increasing electric field over a critical value, part of condensed counterions escape from the PE and become free counterions. The PE starts to be stretched and displays a rod like structure. The values of shape factor and asphericity of the chain show these behaviors too. Moreover, the higher the salt concentration, the higher the critical electric field will be. The critical electric field attains a maximum value when the salt concentration is around equivalence point. For the most compact PE globule, the unfolding critical field E* is determined by equaling the polarization energy and thermal energy(kT). The result gives the relation between the critical field E* and the chain length,E*~N^(-1/2),which can be used in electrophoretic separating of charged, globule biopolymers. The unfolding transition for noncollapsed PE is less pronounced. For elongated PE, we obtained a scaling law,E*~N^(-1). In the last section of study, we analyzed dynamic quantities including mobility of PE, and of condensed ions, and distribution of condensed ions on PE backbone. For small field, condensed counterions bind to PE and slow the mobility of PE. Condensed counterions distribute uniformly on PE backbone. For large field, the condensed counterions overcome the electrostatic interaction and can decondense or glide on the PE backbone. Condensed counterions thus distribute non-uniformly and prefer to stay on one side of PE backbone along the field direction.