Controlled Free Edge Effects in Surface Wrinkling via Combination of External Straining and Selective O2 Plasma Exposure

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• 作者：Yang Yang ; Xue Han ; Weilian Ding ; Shichun Jiang ; Yanping Cao ; Conghua Lu
• 刊名：Langmuir
• 出版年：2013
• 出版时间：June 11, 2013
• 年：2013
• 卷：29
• 期：23
• 页码：7170-7177
• 全文大小：515K
• 年卷期：v.29,no.23(June 11, 2013)
• ISSN：1520-5827

文摘

Herein the edge effect from the traction-free boundary condition is utilized to direct the spontaneous surface wrinkling. This boundary condition is attained by a simple combination of mechanical straining and selective exposure of polydimethylsiloxane (PDMS) substrate to O₂ plasma (OP) through a copper grid. When the strained PDMS sheet is subjected to selective OP treatment, a patterned heterogeneous surface composed of the OP-exposed 鈥渉ard鈥?oxidized SiO_x region (denoted as D₁) and the OP-unexposed 鈥渟oft鈥?region (denoted as D₂) is produced. The subsequent full release of the prestrain (蔚_pre) leads to the selective wrinkling in D₁, rather than in D₂. It is seen that even in D₁, no wrinkling occurs in the vicinity of the D₁ edge that is perpendicular to the wavevector. Furthermore, the average wrinkle wavelength in D₁ (位_D1) is smaller than that of the exposed copper grid-free blank area (位_blank). This wavelength decrement between 位_D1 and 位_blank, which can be used to roughly estimate the edge-effect extent, increases with the applied mesh number of copper grids and exposure duration, while decreases with the increase of 蔚_pre. Meanwhile, there exists a decrease in the amplitude of the patterned wrinkles, when compared with that of the blank region. Additionally, hierarchical wrinkling is induced when the strain-free PDMS substrate is selectively exposed to OP, followed by uniaxial stretching and the subsequent blanket exposure. Consequently, oriented wrinkles perpendicular to the stretching direction are generated in D₂. With respect to D₁, no wrinkling happens or orthogonal wrinkles occur in this region depending on the applied mesh number, exposure duration, and 蔚_pre. In the above wrinkling process, the combinative edge effects in two perpendicular directions that are involved sequentially have been discussed.