Electroosmosis ionic strength

Electroosmotic mobility is proportional to the surface charge density on the silica and inversely proportional to the square root of ionic strength. Electroosmosis decreases at low pH (Si—O —> Si—OH decreases surface charge density) and high ionic strength. At pH 9 in 20 mM borate buffer, electroosmotic flow is 2 mm/s. At pH 3, flow is reduced by an order of magnitude. 

If in the above equations f can be identified with the surface potential % at the experimental surface (or some potential x), and number density of ionizable surface sites, pK of the surface site, position of the hydrodynamic plane of shear, ionic strength, and temperature. 

As previously anticipated, electroosmosis turns out to be negligible as the ionic strength of the soil solution increases, being the result of a minimization of the thickness of the interfacial double layer (see Fig. 3 the concentration of positive ions at the so-called outer Helmholtz plane is sufficient to balance the negative charge present at the soil particle surface). 

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