Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611-6400, USA.
Langmuir. 2009 Nov 17;25(22):12982-9. doi: 10.1021/la901836w.
Translationally symmetric topographies can be designed to induce anisotropy of static and dynamic contact angles. The validity of ignoring directionality of topography in contact angle characterization was evaluated using microscale patterned topographies. Seven patterned topographies comprising elongated discontinuous microfeatures oriented along parallel paths and one topography comprising ridges were fabricated in a poly(dimethyl siloxane) elastomer (PDMSe). The static contact angle, advancing contact angle, receding contact angle, contact angle hysteresis, and slip angle were measured using water on each surface at three in-plane perspectives, with respect to the feature orientation. Static and dynamic contact angle anisotropies were investigated on the topographies to evaluate the effect of discontinuities along the feature lengths on the anisotropy that has been shown on channels or ridges in previous reports. Discontinuous feature topographies exhibited a statistically significant anisotropy of 2 degrees-6 degrees between the perpendicular and parallel directions, with respect to the static and dynamic contact angles. The ridges topography exhibited much larger 5 degrees-42 degrees anisotropy in the contact angles. The discontinuities along the feature lengths greatly reduced, but did not eliminate, the anisotropies compared to the ridges. This evidence of contact angle anisotropy indicates a need to identify the orientation of topography, in relation to contact angle measurements. It also implies a need to consider directionality in the design of microfluidic devices and self-cleaning surfaces.
可以设计具有平移对称性的形貌来诱导静态和动态接触角各向异性。通过使用微尺度图案化形貌来评估忽略形貌在接触角特征中的方向性的有效性。在聚二甲基硅氧烷弹性体（PDMSe）中制造了七种包括沿平行路径取向的拉长不连续微特征的图案化形貌和一种包括脊的形貌。在三个面内视角下，针对每个表面，用水测量了静态接触角、前进接触角、后退接触角、接触角滞后和滑动角，相对于特征取向。在形貌上研究了静态和动态接触角各向异性，以评估沿特征长度的不连续性对先前报道的通道或脊上显示的各向异性的影响。不连续特征形貌在垂直和平行方向之间表现出统计学上显著的 2 度-6 度各向异性，相对于静态和动态接触角。脊形貌在接触角方面表现出更大的 5 度-42 度各向异性。与脊相比，沿特征长度的不连续性大大降低了各向异性，但并未消除。这种接触角各向异性的证据表明，需要确定形貌相对于接触角测量的方向。这也意味着需要在微流控器件和自清洁表面的设计中考虑方向性。
