Theoretical, experimental and numerical scanning probe methodologies for high-resolution surface potential determination of clay particles

The determination of the clay particle surface electrostatic potential is of fundamental importance since it governs the electric force exerted at the clay particle/environment interface which in turn affects, for example, liquid/surface interactions, rheology and organic matter self-assembly and adhesion. Because of the confinement of the electrostatic interactions and of the small size of clay particles, nanoscale resolved methodologies are required to investigate their surfaces. Recent developments of Scanning Probe Microscopy (SPM) have widened the spectrum of possible investigations beyond nanotopography, that can be performed at a nanometric level on the surface of single clay particles. Electric Force Microscopy (EFM), Kelvin Probe Force Microscopy (KPFM) and Multimode EFM (MM-EFM) have been developed for surface potential determination. This paper reports on both a theoretical and an experimental approach based on EFM, KPFM and MM-EFM observations of layer silicate surfaces typical of clays.