Understanding the effects of surface roughness on the temperature and pressure relevancy of water contact angles

Surface roughness coupled with temperature and pressure is expected to show synergistic effects on contact angle. Nonetheless, the influence of surface roughness at elevated temperatures and pressures has not been clearly understood. This study investigates experimentally how surface roughness affects the temperature- and pressure-dependent water contact angles for 304 stainless steel. The temperature and pressure were first raised up to 320 ℃ (a record high value compared to previous studies) and 15 MPa, respectively, at the same time. The analysis of the interfacial tensions was finally made based on the measured results. It was revealed that roughness exhibits significant effects at lower pressures and its influence can be weakened by raising the pressure. The increase of roughness can exaggerate the pressure dependence of water contact angle below 160 ℃, while little change was found at temperatures over 160 ℃. Similarly, the effects of roughness on water contact angle were mainly observed below 120 ℃: the water contact angle increases with decreasing the roughness. However, roughness seems to cause weak differences on water contact angles at higher temperatures. In summary, surface roughness presents remarkable impact on surface wettability, mainly at low temperatures and pressures. Moreover, compared to temperature dependence, the pressure-related water contact angles are more sensitive to roughness alteration.