Electrical double layer interactions between soil colloidal particles: Polarization of water molecule and counterion

The electrical double layer (EDL) interactions strongly affect aggregation and dispersion of soil colloidal particles. In this research a modified model taking the polarization of water molecule and counterion into account was proposed based on nonlinear Poisson-Boltzmann theory to describe electrostatic interaction. The polarizations of both the counterion and the water molecule can increase the interaction between ion/water and soil particle surface, and then decrease the surface potential. Particle surface potential also depends on the surface separation when the EDL overlaps. The midpoint potential between colloidal particles decreases with increase of ion polarization but increases in the presence of water polarization through the change of the double layer thickness. Both the electrostatic repulsive pressure between soil particles and its force range increase markedly in the presence of the polarization of water molecules, but decrease with increase of counterion polarization. The water molecule polarization, rather than the counterion polarization, contributes more to EDL interactions. The counterion polarization is the origin of Hofmeister effects of the EDL interactions, which is affected by water polarization. The theoretical predicted force curve between clay particles by the modified model was verified by the experimental determination of surface force. In addition, the hydration force, fitted to a double exponential decay function, can be estimated by subtraction of the electrostatic interaction force based on DLVO theory from that based on the present model.