Patterning of worm-like soft polydimethylsiloxane structures using a TiO₂ nanotubular array

Patterned polydimethylsiloxane (PDMS) is an important structure for soft lithography. Various materials have been deployed as mold for patterning PDMS. Anodized nanotubular array has been sought after as cost-effective alternative for textured silicon. An array of TiO2 nanotubes with characteristic diameter ≈140 nm and the length of ≈1.5 microns, created by anodic oxidation of a titanium substrate, was used here as a template for soft PDMS molding. The optimal molding process was developed by a combination of silanization, use of solvent, application of a vacuum, and hydraulic pressing. The silanization was confirmed by Fourier transform infrared spectroscopy and contact angle measurements while the PDMS structure was examined by scanning electron microscope and energy dispersive X-ray spectroscopy. Hydraulic pressing significantly improved the infiltration of PDMS into the pores of nanotubular array resulting in formation of PDMS nanobumps after separation of the polymer from the template. Complete infiltration of PDMS precursor into the avity of nanotubes was observed on the hydraulic-pressed sample without toluene impurities. The hydraulic-pressed samples exhibited higher adhesion strength than nonpressed ones. The adhesive strength was measured by a simple experimental arrangement, in which the PDMS layer was stuck on a vertical glass surface followed by pulling it downwards.