Abstract
The soft lithographic fabrication of high-aspect-ratio polydimethylsiloxane (PDMS) microstructures is quite challenging because of the strong interfacial adhesion between them and masters during demolding. This paper presents a simple method for fabricating high-aspect-ratio PDMS microstructures by reducing the interfacial adhesion through the cooling process. The effect of cooling process on the topography, elastic property, and adhesion property of Sylgard 184 PDMS is studied. It is found that wrinkles are formed on the surface of PDMS and that the Young’s modulus of PDMS is increased by the air cooling process. Consequently, the air-cooled PDMS has lower adhesion than the traditional oven-cooled PDMS. This result could be explained by the adhesion parameter theory: both the high amplitude of the wrinkles formed on the surface of PDMS and the high Young’s modulus of PDMS increase separation forces and reduce adhesive forces in the interface. Application of this method is demonstrated by fabricating PDMS microchannels from a silicon master which has microstructures with different aspect ratios. Compared with PDMS microchannels obtained by the oven cooling process, PDMS microchannels with a depth of 200 μm and an aspect ratio of 10 are successfully fabricated by the air cooling process.
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