Comparison of light scattering of colloidal dispersions with direct force measurements between analogous macroscopic surfaces

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Abstract
The equilibrium force laws (force vs distance) between two macroscopic surfactant-coated mica surfaces separated by organic liquids have been determined. The aim was to ascertain whether directly measured forces are able to be employed in the prediction of second virial coefficients as obtained from light scattering experiments on analogous colloidal suspensions (i.e., spherical particles coated with the same surfactant and dispersed in the same medium). The quantitative agreement between the two independent measurements was excellent. This suggests that the interaction energy per unit area, which governs the physical properties of a bulk colloidal system, is indeed, the same as the equilibrium interaction energy per unit area of two macroscopic surfaces, for the systems investigated here. Such a correlation has been tacitly assumed in the past, and it is the first time that this assumption has been confirmed experimentally for any system.