Charged Soft Matter in Motion - How to Deal with Electrohydrodynamical Problems

The dynamic behavior of polyelectrolyte chains in the oligomer range
is investigated with coarse grained molecular dynamics simulation and
compared to data obtained by two different experimental methods,
namely capillary electrophoresis and PFG- NMR. We find excellent
agreement of experiments and simulations when hydrodynamic
interactions are accounted for in the simulations. We show that the
electrophoretic mobility exhibits a maximum in the oligomer range and
for the first time illustrate that this maximum is due to the
hydrodynamical shielding between the chain monomers. Our findings
demonstrate convincingly that it is possible to model dynamic behavior
of polyelectrolytes using coarse grained models for both, the
polyelectrolyte chains and the solvent induced hydrodynamic
interactions.[1]

We furthermore present a novel estimator for the dynamical effective
charge of strongly charged polyelectrolyte chains during free solution
electrophoresis. The effective charge is used to evaluate the scaling
behavior of the hydrodynamic friction of the polyelectrolyte-
counterion-complex. We show that the hydrodynamic friction during free
solution electrophoresis is linearly depending on the chain length.
This scaling differs from the scaling of the hydrodynamic size. This
difference can be attributed to the counter ion association.[2]

Additionally, we use the developed model to study the process of end-
labeled free-solution electrophoresis (ELFSE). The hydrodynamic
friction of polyelectrolyte chains is altered by attaching uncharged
polymeric labels to the ends. This restores size-dependent
electrophoretic mobility for longer polyelectrolyte chains in free
solution electrophoresis. The charge estimators are used to quantify
the alteration of the hydrodynamic friction for various flexible
labels. Finally, the results are compared to theoretical predictions.
[3]

References

[1] K. Grass, U. Böhme, U. Scheler, H. Cottet, and C. Holm. Phys. Rev.
Lett. 2008, 100, 096104.

[2] K. Grass, and C. Holm, Journal of Physics Cond. Mat. 20, 494217
(2008).

[3] K. Grass, G. Slater, and C. Holm. submitted.