**3. Methods for characterization of colloidal slurry phases**

Potential determining ions [H+ and OH− ] at the interface plays a very important role in determining electrical charge at the surface in the colloidal system [12–15]. There are many diagnostic methods such as particle size analysis and turbidity measurements, surface force measurement with atomic force microscope (AFM) and surface force apparatus (SFA) are direct approaches for studying colloidal interactions, which could provide insights into molecular mechanisms of operating colloidal forces with high resolution [1]. After invention of these advanced techniques, these have become the most important tools in colloid and interface science to directly measure the interactions between particles and liquid substrates, and even the single molecular force involved in the rupture of a single chemical bond and the stretching of polymer chains. These are not only limited to hard or non-deformable surfaces, are also used to measure the forces between one solid particle and an air bubble or an oil drop. Although progress has been made in studying bubble-particle interactions using AFM in recent years, the deformation of the bubble by both the hydrodynamic and surface forces remains a bottleneck in determining the absolute separation and the surface forces.
