Screening in Yukawa fluid mixtures

Abstract

The effective pair potential between mesoscopic charged particles in a neutralising background medium takes a Yukawa form $\exp (-\lambda r)/r$ with screening length ${\lambda }^{-1}$. We consider a dilute suspension of such Yukawa particles dispersed in a solvent with correlation length $\xi <{\lambda }^{-1}$ and show that the Yukawa interaction is `screened' if the pair potentials between solvent particles exhibit Yukawa decay with the same screening length ${\lambda }^{-1}$. However, if the solvent pair potentials are shorter ranged than the solute Yukawa potentials, then the effective potential between pairs of solute particles is `unscreened', i.e. the effective potential between the solute particles is equal to the bare potential at large particle separations.

4 pages, 2 figures, accepted for publication in Phys. Rev. E