Long-Range Electrostatic Attraction between Similar, Charge-Neutral Walls

Long-range attractive forces between electrically neutral, glass surfaces, a sphere and a plane are measured directly with an atomic force microscope. Charge neutrality is achieved by immersion in cationic surfactant solutions. The forces are much larger in magnitude than dispersion forces. Over a wide range of ionic strength (Debye length κ^-1), achieved by addition of salt [ ρₜₒₜₐₗ0ex0ex=0ex0ex(10^-5-10^-2)M], the energy of interaction decays asymptotically as ρₜₒₜₐₗexp(-2κD)/κD. Both the pseudoexponential behavior and the dependence of the prefactor upon the ionic strength suggest an electrostatic mechanism.