Mixed Wettability Microfluidics: Fabrication, Experimental Validation, and Numerical Simulation

Subsurface reservoirs often exhibit heterogeneous wettability patterns, named mixed wettability, which critically influence multiphase fluid flow dynamics and trapping mechanisms. To investigate these effects at the pore scale, microfluidic systems have become crucial. Despite their utility, the fabrication of microfluidic devices with precisely controlled spatial distributions of mixed wettability remains a significant challenge. This study presents a novel fabrication approach that combines photolithography and molecular vapor deposition (MVD) of perfluorodecyltrichlorosilane (FDTS) to engineer micromodels with defined mixed wettability configurations. Two micromodel designs were developed to emulate the wettability complexities of natural porous media, including single channels with horizontal and vertical wettability transitions. Two-phase flow experiments were conducted using high-resolution microscopy and high-speed imaging to capture dynamic pore-scale phenomena. Experimental observations highlighted the profound effect of mixed wettability on the behavior of two-phase fluids. Specifically, the meniscus shape shifted from convex to concave as fluids moved between hydrophobic and hydrophilic areas. In channels with vertical variations in wettability, the fluid interface formed a distinctive S-shape. These observations were complemented by numerical simulations using the phase-field method in COMSOL Multiphysics®, enabling validation of the experimental results. The simulations closely matched experimental findings, highlighting the efficiency of the fabrication technique and the reliability of the experimental and numerical methods. This work provides a robust platform for studying the interplay between mixed wettability and multiphase flow, offering valuable insights for applications in subsurface energy systems, including oil recovery, CO2 sequestration, and hydrogen storage.