Effect of Roughness Geometry on Wetting and Dewetting of rough PDMS Surfaces

M. Kanungo, S. Mettu, K-Y Law
Xerox Research Corporation, US

Keywords: wetting, spreading, PDMS microstructures, roughness geometery

Summary:

Wetting and spreading of a liquid on a solid surface is of great interest in both fundamental research and practical applications such as liquid flow in microfluidic devices, coating and printing. Recently, printing has evolved as a manufacturing technology for fabrication of functional devices for sensors, displays, solar cells and microfluidics. Understanding and controlling interactions between ink and substrates are keys to successful implementation of ink printing in additive manufacturing of the components and devices. However, most practical surfaces are not atomically smooth and have a random roughness, effect of which on wettability is difficult to characterize. The present study aims to systematically study the effect of roughness geometry (e.g., frequency, peaks or valleys) on the wetting and de-wetting behaviors of liquid on print surfaces. The model rough PDMS surfaces comprise arrays of 3µm hemispherical bumps and cavities with pitches varying from 4.5 to 96 µm fabricated by photolithography and molding process. Results show that the microtextures on the PDMS surfaces have profound effects on the wetting and de-wetting performance. The effects of the Wenzel roughness factor (r), the roughness geometry on both wetting and dewetting under both static and dynamic conditions are highlighted.