Suh Kahp Y, Jon Sangyong
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea.
Langmuir. 2005 Jul 19;21(15):6836-41. doi: 10.1021/la050878+.
We demonstrate that wettability of poly(ethylene glycol) (PEG) surfaces can be controlled using nanostructures with various geometrical features. Capillary lithography was used to fabricate PEG nanostructures using a new ultraviolet (UV) curable mold consisting of functionalized polyurethane with acrylate group (MINS101m, Minuta Tech.). Two distinct wetting states were observed depending of the height of nanostructures. At relatively lower heights (< 300 nm for 150 nm pillars with 500 nm spacing), the initial contact angle of water was less than 80 degrees and the water droplet easily invaded into the surface grooves, leading to a reduced contact angle at equilibrium (Wenzel state). At relatively higher heights (> 400 nm for 150 nm pillars with 500 nm spacing), on the other hand, the nanostructured PEG surface showed hydrophobic nature and no significant change in contact angle was observed with time (Cassie state). The presence of two wetting states was also confirmed by dynamic wetting properties and contact-angle hysteresis. The wetting transition from hydrophilic (bare PEG surface) to hydrophobic (PEG nanostructures) was described by the Cassie-Baxter equation assuming that enhanced hydrophobicity is due to the heterogeneous wetting mediated by an air pocket on the surface. The measured contact angles in the Cassie state were increased with increasing air fraction, in agreement with the theoretical prediction.
我们证明，聚乙二醇（PEG）表面的润湿性可以通过具有各种几何特征的纳米结构来控制。采用毛细管光刻技术，使用一种由含丙烯酸酯基团的功能化聚氨酯组成的新型紫外（UV）可固化模具（MINS101m，Minuta Tech.）来制备PEG纳米结构。根据纳米结构的高度观察到两种不同的润湿状态。在相对较低的高度（对于间距为500 nm的150 nm柱体，高度<300 nm），水的初始接触角小于80度，水滴容易侵入表面凹槽，导致平衡时接触角减小（文策尔状态）。另一方面，在相对较高的高度（对于间距为500 nm的150 nm柱体，高度>400 nm），纳米结构化的PEG表面表现出疏水性，且接触角随时间没有明显变化（卡西状态）。动态润湿特性和接触角滞后也证实了两种润湿状态的存在。从亲水性（裸露的PEG表面）到疏水性（PEG纳米结构）的润湿转变由卡西-巴克斯特方程描述，假设疏水性增强是由于表面气穴介导的非均匀润湿。在卡西状态下测得的接触角随着空气比例的增加而增大，与理论预测一致。
