A simple fabrication process for stepwise gradient wrinkle pattern with spatially-controlled wavelength based on sequential oxygen plasma treatment

- We suggested a simple and efficient fabrication method for stepwise gradient wrinkle pattern based on sequential plasma treatment.
- Glass plate was used as an effective blocking mask for oxygen plasma to modulate the plasma dose in the specific regions.
- The stepwise gradient wrinkle pattern was fabricated with three regions of uniform feature size.
- The utility of the stepwise gradient wrinkle pattern as a screening platform was evaluated by measuring CA, CAH and transmittance.

Though a gradient surface wrinkle pattern has drawn much interest recently, the previous efforts have been limited to the generation of continuous gradient patterns of surface wrinkle with gradually varying wavelengths. Here, we report a simple fabrication process for a stepwise gradient wrinkle pattern which has spatially-controlled discrete wavelengths in distinct regions with clear boundary on a polydimethylsiloxane (PDMS) substrate. The stepwise gradient wrinkle pattern is achieved based on the sequential treatment of oxygen plasma for the PDMS surface using a glass plate as an effective blocking mask for the plasma, resulting in the modulation of plasma dose on the specific regions of the PDMS surface. We fabricated a stepwise gradient wrinkle pattern on three regions of uniform feature size with 540, 840, and 1240 nm in wavelength and 60, 110, and 220 nm in depth. The utility of the stepwise gradient wrinkle pattern as a platform for screening global surface properties induced by a number of wrinkle patterns was evaluated by assessing the difference of anisotropic wetting behavior and transmittance depending on wrinkle feature sizes. This fabrication method can be easily implemented in microfluidic and optical applications investigating effects of various wrinkle groove patterns.

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