Steric effect of water molecule clusters on electrostatic interaction and electroosmotic transport in aqueous electrolytes: a mean-field approach

We theoretically study the size effect of water molecule clusters not only on electrostatic interaction between two charged surfaces in an aqueous electrolyte but also on electroosmotic transport in a nanofluidic channel. Applying a free energy based mean-field approach accounting for different sizes of ions and water molecule clusters, we derive a set of coupled equations to compute electrostatic and electroosmotic properties between charged surfaces. We verify that the smaller the size of a water cluster, the stronger the electroosmotic transport in nanofluidic channels. In addition, we find that an increase in size of a water cluster yields a decrease in electrostatic interaction strength between similar or oppositely charged planar surfaces.