Article,
Polyelectrolytes in electric fields
Journal Of Physical Chemistry B, 107 (32): 8208--8217 (August 2003)
Abstract
We investigate the effect of an electric field on a highly charged
polyelectrolyte, (PE) chain by Brownian-dynamics simulation methods
and a combination of different scaling arguments. In the simulation
we take the counterions explicitly into account and therefore include
the effects of counterion condensation and PE collapse as the coupling
parameter (proportional to counterion valency) is increased. For
highly charged PEs in the collapsed phase, a norrequilibrium unfolding
transition occurs at sufficiently high electric fields where the
PE aligns parallel to the external field. The critical field strength
E* is determined from scaling results for the polarizability of a
PE globule and exhibits a dependence on the chain length N, E* similar
to N-1/2, which might be useful for electrophoretic separation of
charged, collapsed biopolymers. For noncollapsed PEs this unfolding
transition is less pronounced: the critical field depends on the
swelling exponent v and scales as E* similar to N-3v/2 The electrophoretic
mobility of PE monomers and counterions is determined. For large
fields, counterions bound to the PE contribute significantly to the
total conduction, since they can glide along the PE. This is an important
factor in understanding experimental conduction experiments. The
electrophoretic mobility of the bound counterions is determined by
the electrostatic friction with the PE backbone and an activation
barrier for decondensing from the PE; it in fact changes sign as
the field strength is increased.
Tags
- collapse
- condensation;
- counterion
- diffusive
- dna-molecules;
- driven
- dynamics
- electrophoresis;
- mobility;
- molecular-dynamics;
- phase-transitions;
- precipitation;
- simulation;
- systems;
