IDENTIFYING ELECTROSTATIC INTERACTIONS IN AQUEOUS AND NON-AQUEOUS MEDIA USING ATOMIC FORCE MICROSCOPY AND EXTENDED DLVO THEORY

An understanding of colloidal stability in non-aqueous solutions is vital to the petroleum industry as it addresses the accumulation properties of aging products (fine engine metal particulates) in motor oils. Increased knowledge of the forces that dictate the accumulation of aging products will help improve motor oil lifetimes and efficiencies. Motor oil additives that improve oil efficiency often contain Zn, Ca, Mo, and Cu, which can influence colloidal electrostatic interactions and decrease coagulation of particulates, thus reducing the filtration of aging products from oils. The use of urea as an additive can help minimize the repulsive interactions between particulates, and enhance coagulation and increase filtration.

Atomic Force Microscopy (AFM) has been used to measure nanoNewton and picoNewton forces between polystyrene microspheres and a glass surface in a non-polar decane solution, as well as in distilled water. Preliminary results show that electrostatic interactions, which dominate colloidal stability in aqueous solutions, were significantly reduced in the non-polar decane solution. Extended-DLVO (XDLVO) theory will be used to describe the van der Waals, electrical double layer, and acid/base interactions based on the total free energy (ΔG^Total) of each system. Future investigations consist of measuring contact angles and zeta-potentials in order to determine ΔG^Total of a system, which will provide a description of the XDLVO theory variables.