Fragile structured layers on surfaces in highly concentrated solutions of electrolytes of various valencies

In the present study a dynamic mode of atomic force microscopy for force measurements was employed to investigate the hydration repulsion force between charged surfaces in highly concentrated electrolyte solutions of NaCl, MgCl2 and LaCl3. A strong dependence of this repulsive force on the approaching rate of surfaces, the prehistory of their contact and the valency of cations was demonstrated. The phenomena were strongly pronounced in the cases of high scan rates, large surfaces and cations of high valency. The results obtained indicate that a fragile structure composed of water molecules, ions and hydrated ions exists outside of the primary layer of water molecules and ions adsorbed firmly on surfaces.