Abstract
In this present work, we aim to improve the hydrophobicity of a polydimethylsiloxane (PDMS) surface. Various heights of 3D PDMS micropillars were fabricated via grayscale photolithography, and improved wettability was investigated. Two approaches of PDMS replication were demonstrated, both using a single master mold to obtain the micropillar arrays. The different heights of fabricated PDMS micropillars were characterized by scanning electron microscopy (SEM) and a surface profiler. The surface hydrophobicity was characterized by measuring the water contact angles. The fabrication of PDMS micropillar arrays was shown to be effective in modifying the contact angles of pure water droplets with the highest 157.3-degree water contact angle achieved by implementing a single mask grayscale lithography technique.
Highlights
A solid surface’s hydrophobicity is the physical property that makes it water repellent and non-wettable
We aim to investigate the impact of grayscale photolithography on fabricating various heights of 3D micropillars, simultaneously using only a one-layer mask in improving the hydrophobicity of the PDMS surface towards being superhydrophobic
We have successfully demonstrated the improved hydrophobicity of a PDMS surface by changing its surface roughness using a single mask grayscale lithography technique
Summary
A solid surface’s hydrophobicity is the physical property that makes it water repellent and non-wettable. As there is no continuous flow in an open microfluidic application, super hydrophobic surfaces are required to form water droplets. The fabrication technique of a micro three-dimensional (3D) structure on a PDMS surface with a high-aspect ratio (HAR) is one of the alternatives to realize a PDMS-based pipetting-free droplet array. A modification in conventional photolithography to fabricate high aspect ratio structures with a standard binary mask is demonstrated in order to achieve a reliable fabrication method for microfluidic devices [9]. The purpose of this research is to improve the surface roughness of hydrophobic materials by implementing a grayscale lithography technique with a single exposure process. Because it is initially hydrophobic, PDMS is an excellent example of such materials
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