Title: Engineering Wettability from the Nano- to the Macroscale
Advisor: Jacob Israelachvili
Wettability describes the adhesion affinity of a fluid (liquid or vapor) phase to a solid surface in the presence of another fluid phase (e.g., air). For example, a hydrophilic (water-loving) surface is one on which water “wets”, spreads, or sticks/adheres to well. On the other hand, hydrophobic (water-hating) surfaces are ones on which water does not wet or adhere to well. Wetting of liquids on surfaces has implications for diverse applications ranging from cleaning and personal care products to oil recovery. Depending on the application, it may be desirable for a system to be hydrophilic or hydrophobic, or – in other applications – oleophilic or oleophobic (oil-loving or oil-hating, respectively), or even omniphilic or omniphobic (both water and oil-loving or -hating, respectively). This thesis presentation explores different physical and chemical mechanisms that can be utilized to engineer the desired wettability of both liquid/vapor/solid and liquid/liquid/solid systems.
The first part of this presentation explores how the desired macroscopic wettability can be engineered (possible to render intrinsically hydrophilic surfaces into hydrophobic surfaces) by utilizing nano- and micro-scale surface textures and features, without changing the chemistries (i.e., the actual components) of the system. In particular, we developed and experimentally demonstrated a model for a priori predicting the different possible equilibrium wettability states for all types of rough/patterned/textured surfaces. We also studied the stability of the different possible texture-induced wetting states to distinguish between metastable (metastability can range from not stable to stable for a few seconds or minutes to 20+ days) versus thermodynamically stable states.
The second part of this presentation touches upon our work on engineering the wettability of crude oil/brine water/rock systems for improving oil recovery. In this work, we studied the mechanisms that occur at the nano- and micro-scale by which the wettability of geologic-scale petroleum reservoir systems is affected by tuning the composition of the brine water that is injected to displace and recover trapped reservoir oil. In particular, we found that decreasing the salinity of the injection brine water into carbonate oil reservoirs activates three interrelated physico-chemical mechanisms that work together to decrease the adhesion energy between the crude oil and rock across the brine water film and ultimately results in improved oil detachment and removal from the rock surfaces.