Department of Civil Engineering, McMaster University, Hamilton, Ontario L8S 4L8, Canada.
Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4L8, Canada.
Langmuir. 2023 Feb 21;39(7):2529-2536. doi: 10.1021/acs.langmuir.2c02719. Epub 2023 Feb 10.
Wettability plays a significant role in controlling multiphase flow in porous media for many industrial applications, including geologic carbon dioxide sequestration, enhanced oil recovery, and fuel cells. Microfluidics is a powerful tool to study the complexities of interfacial phenomena involved in multiphase flow in well-controlled geometries. Recently, the thiolene-based polymer called NOA81 emerged as an ideal material in the fabrication of microfluidic devices, since it combines the versatility of conventional soft photolithography with a wide range of achievable wettability conditions. Specifically, the wettability of NOA81 can be continuously tuned through exposure to UV-ozone. Despite its growing popularity, the exact physical and chemical mechanisms behind the wettability alteration have not been fully characterized. Here, we apply different characterization techniques, including contact angle measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) to investigate the impact of UV-ozone on the chemical and physical properties of NOA81 surfaces. We find that UV-ozone exposure increases the oxygen-containing polar functional groups, which enhances the surface energy and hydrophilicity of NOA81. Additionally, our AFM measurements show that spin-coated NOA81 surfaces have a roughness less than a nanometer, which is further reduced after UV-ozone exposure. Lastly, we extend NOA81 use cases by creating (i) 2D surface with controlled wettability gradient and (ii) a 3D column packed with monodisperse NOA81 beads of controlled size and wettability.
润湿性在许多工业应用中控制多孔介质中的多相流起着重要作用，包括地质二氧化碳封存、提高石油采收率和燃料电池。微流控技术是研究多相流中涉及的界面现象复杂性的有力工具，在良好控制的几何形状中。最近，一种名为 NOA81 的基于硫醇的聚合物作为制造微流控器件的理想材料出现，因为它结合了传统软光刻的多功能性和广泛的可实现润湿性条件。具体来说，NOA81 的润湿性可以通过暴露于 UV-臭氧来连续调节。尽管它越来越受欢迎，但润湿性改变的确切物理和化学机制尚未完全表征。在这里，我们应用不同的表征技术，包括接触角测量、X 射线光电子能谱 (XPS) 和原子力显微镜 (AFM) 来研究 UV-臭氧对 NOA81 表面化学和物理性质的影响。我们发现，UV-臭氧暴露会增加含氧极性官能团，从而提高 NOA81 的表面能和亲水性。此外，我们的 AFM 测量表明，旋涂的 NOA81 表面粗糙度小于一纳米，暴露于 UV-臭氧后进一步减小。最后，我们通过创建（i）具有受控润湿性梯度的 2D 表面和（ii）填充具有受控尺寸和润湿性的单分散 NOA81 珠的 3D 柱来扩展 NOA81 的用途。
