Effects of Temperature and Pressure on the Dynamic Contact Angles of Water on Roughened Surfaces under Low Capillary Number

Understanding dynamic wetting behavior under extreme temperatures and pressures is critical for applications such as enhanced oil recovery and nuclear power systems. This study systematically investigates the effects of temperature and pressure on the dynamic advancing and receding contact angles (DACA and DRCA) of water on roughened 304 stainless steel surfaces under low capillary number conditions (Ca < 10^-5). Six surfaces with varying roughness (0.017 μm ≤ Sa ≤ 0.453 μm) were characterized, and experiments were conducted at temperatures up to 100 °C and pressures up to 10 MPa. The results show that the DACA generally increases with both temperature and pressure. Notably, a distinct roughness-pressure coupling effect was identified: while the DACA on smooth surfaces increased linearly with pressure, rough surfaces exhibited nonlinear responses. This nonlinearity is attributed to pressure-induced transitions in the wetting state within surface textures. In contrast, the DRCA on rough surfaces remained low and independent of thermodynamic conditions due to dominant pinning by macroscopic defects. However, on the ultrasmooth surface, elevated temperature activated a pinning mechanism, sharply reducing the DRCA and shifting the receding mode from constant contact angle to a mixed mode. These findings offer fundamental insights into dynamic wetting under extreme conditions, aiding the design of functional surfaces for high-pressure and high-temperature environments.