Monday, January 30, 2012

1201.5638 (Sahin Buyukdagli et al.)

Excluded volume effects in macromolecular forces and ion-interface
interactions
   [PDF]

Sahin Buyukdagli, T. Ala-Nissila
A charged Yukawa liquid confined in a slit nanopore is studied in order to
understand excluded volume effects in the interaction force between the pore
walls. A previously developed self-consistent scheme (S. Buyukdagli el al., J.
Stat. Mech. P05033 (2011)) and a new simpler variational procedure that
self-consistently couple image forces, surface charge induced electric field
and pore modified core interactions are used to this aim. For neutral pores, it
is shown that with increasing pore size, the theory predicts a transition of
the interplate pressure from an attractive to a strongly repulsive regime
associated with an ionic packing state, an effect observed in previous Monte
Carlo simulations for hard core charges. The role of the range of core
interactions in the ionic rejection and interplate pressure is thoroughly
analyzed. We show that the physics of the system can be split into two
screening regimes. The ionic packing effect takes place in the regime of
moderately screened core interactions characterized with the bare screening
parameter of the Yukawa potential b<3/lB, where lB is the Bjerrum length. In
the second regime of strongly screened core interactions b>3/lB, solvation
forces associated with these interactions positively contribute to the ionic
rejection driven by electrostatic forces and enhance the magnitude of the
attractive pressure. The pronounced dependence of the interplate pressure and
ionic partition coefficients on the magnitude and the range of core
interactions indicates excluded volume effects as an important ion specificity
and a non-negligible ingredient for the stability of macromolecules in
electrolyte solutions.
View original: http://arxiv.org/abs/1201.5638

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