Magnetic effects on thickness of adsorbed layer in aqueous solutions evaluated directly by atomic force microscope

The short-range interaction force between a mica surface and an AFM probe tip in electrolyte solutions was measured by atomic force microscopy (AFM) to directly evaluate the thickness of the adsorbed layer on the surface. The magnetic effects were estimated by comparing the thickness in the magnetized solution with that in nonmagnetized solution. It was found that (i) the magnetic exposure thickens the adsorbed layer on the surface in electrolyte solutions, (ii) the magnetic effects are easily destroyed by the external disturbance, (iii) there exists a memory in the magnetic effects, which remains for at least a day, (iv) the magnetic effects appear mostly in the solutions of structure-disordering cations, such as Cs⁺, Rb⁺, and K⁺, and (v) the results are consistent with those obtained in preceding macroscopic experiments. It is hypothesized from these results that the water molecules weekly bound around the structure-disordering ions are quasistabilized and structured by the magnetic exposure and that the magnetic thickening of the adsorbed layer is caused by the adsorption of these structured ions on the surface.