Flexible PDMS microtubes for examining local hydrophobicity

In this work, utilizing commercial glass micropipettes as molds, polydimethylsiloxane (PDMS) microtubes have been successfully fabricated. Such a microtube can be as long as 3 cm, its sidewall has a thickness in the range of 4-10 mu m, and the outer and inner diameters of its tip can be as small as 26 and 17 mu m, respectively. Compared with the rigid glass micropipette, the PDMS microtube is soft, making it flexible. The flexibility enables the PDMS microtube: (1) to be bendable for easily delivering liquid drops to confined locations, and (2) to have less damage to the contacted substrate. Its small tip makes it have access to narrow gaps, such as microgrooves. Three types of tests have been done to explore water-delivery properties of PDMS microtubes. Based on the understanding gained from these tests, a PDMS microtube is directly applied to examine local wetting properties of lotus and SU-8 micropillars.