Coupling with colloidal forces

The interaction forces and potentials between two charged surfaces in an electrolyte are fundamental to the analysis of colloidal systems and are associated with the formation of electrical double layers (EDLs) in vicinity of the solid surfaces. The charged surfaces typically interact across a solution that contains a reservoir of ions, as a consequence of the dissociation of the electrolyte that is already present. In colloid and interfacial sciences, the EDL interaction potential, coupled with the van der Waals interaction potential, leads to the fimdamental understanding of inter-siuface interaction mechanisms, based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory [1]. In practice, the considerable variations in the EDL interaction, brought about by the variations in electrolytic concentration of the dispersing medium, pH of the medium, and the siuface chemistry, lead to a diverse natiue of the colloidal behavior. A fundamental understanding of the physics of EDL interactions, therefore, is of prime importance in... 

The most significant advance since the development of the SFA came when Ducker and co-workers (26, 27) glued a super-colloidal silica sphere on to an Atomic Force Microscope (AFM) cantilever and used the AFM to measure the forces between the sphere and a flat glass surface. The simplicity and reliability of the technique, coupled with its accessibility and the fact that interferometry is not required, means that it has revolutionized surface force measurement and allowed a wealth of substrates to be examined (28-43). 

It should be mentioned that the above results are vahd if the hydrodynamic interactions do not affect particle transport through the adsorption layer of thickness 2a. This seems justified for smaller colloid particles and proteins. However, for micrometer-sized particles placed in shearing flows, the hydrodynamic forces play a significant role due to the coupling with the repulsive electrostatic interactions. This leads to enhanced blocking effects called hydrodynamic scattering effects and discussed extensively in recent review works [7,14]. These results have been interpreted theoretically in terms of the Brownian dynamics simulations [14], which are, however, considerably more time-consuming than the RSA simulations. 

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