A study of complex solid-liquid interfaces by atomic force microscopy

In this thesis, we have studied the interaction forces at the solid-liquid interface of various complex systems using atomic force microscopy. Starting from a simple silica-electrolyte interface, we have increased the complexity of the system step-by-step. On the electrolyte side, we have increased the complexity by increasing the concentration of simple salt solutions where ion correlation effects become no longer negligible. Effects of complex brines such as artificial seawater and (rock)formation water were also investigated. On the solid side, we have studied the interactions induced by a dynamic mineral, calcite. Even in simple brines, the interaction at the calcite-electrolyte interface cannot be fully described by DLVO theory. Then, we looked at a particular example of low-salinity improved oil recovery in carbonate reservoirs. For this, we mimicked the reservoir conditions in the laboratory by subjecting both the mineral (calcite) and the fluids (formation water, crude oil) to certain ageing procedures. We examined each step of the ageing procedure to understand how a hydrophilic mineral surface became hydrophobic. Finally, we tracked the changes occurring on the aged mineral surface upon exposure to brines of various salinity to study the low-salinity effect.