Novel Mixed Wettability Coating: Application in Microfluidics Fabrication

Microfluidics is an emerging technology that has gained attention by the industry for its capabilities to investigate and visualize fundamental recovery mechanisms at the pore scale in a microdevice, mimicking, to some extent, the actual rock pore-network. While current technologies are capable of building micromodels that are either water-wet or oil-wet, a technique to achieve a representative mixed-wet property is still unreached. In this work, we introduce a novel surface coating capability using thin film deposition to fabricate surfaces with selective wettability, oil-wet and water-wet, an effort to mimic actual mixed-wet rock. This unique approach enables the generation of hydrophobic surfaces in selected regions by altering the hydrophilic surface property of silicon substrate at the microscale. A selective wettability control mask and Perfluorodecyltrichlorosilane (FDTS) hydrophobic coating using molecular vapor deposition (MVD) were used for surface wetting properties alteration. Surface measurements, including contact angle measurements, X-ray photoelectron spectroscopy (XPS), and Transmission Electron Spectroscopy (TEM) imagining, were performed to evaluate the thin-film composition and morphology. By altering the wetting state of the substrate by the coated film, a selective mixed wettability surface was achieved. This technique has the potential to be utilized in microfluidic device developments. Tuning the wetting state of the substrate to mimic the mixed-wet characteristics of reservoir rocks, such as carbonates and shales, can enhance our understanding of complex fluid behaviors in porous media and provide a crucial contribution to many subsurface petroleum engineering applications such as enhanced oil recovery (EOR) and CO2 storage.