- Electrostriction. Ions diffusing (or being subject to flow, for that
matter) through a matrix that carries an electrical charge, will be
subject to an additional retarding effect, caused by electrostatic
attraction. The strength of this effect depends on the ratio of the
average distance between ion and charged surface over the Debye
length (thickness of the electric double layer; Section 6.3.2).
Consequently, the retarding effect will be stronger for narrower
pores and for a lower ionic strength.
FIGURE5.15 Relative diffusion coefficientDðlÞ=D 0 as a function ofl¼rm=rpfor
diffusion of spherical molecules of radiusrmthrough a cylindrical capillary of radius
rp; calculated according to Eq. (5.26).