In this work, we address the issue of controlled modification of the surface topography of polydimethylsiloxane ͑PDMS͒ when subjected to oxygen-based plasma treatments, and we investigate the resulting enhanced surface area as a means of controlling the surface wetting properties. We fabricate wavy structures of controllable nanoscale amplitude and periodicity in the range 50-300 nm, spontaneously formed on PDMS surfaces, by means of appropriate plasma processing conditions and radiation pretreatment. Such structures are desirable for applications in sensor microdevices, the development of biocompatible materials, and micro-and nanosystems in general. Ordered structures fabricated on polydimethylsiloxane of relatively high amplitude and small periodicity are chosen as appropriate surfaces for the enhancement of the surface wetting properties, which can be tuned from highly hydrophilic to hydrophobic when combined with a hydrophobic coating applied on the rich surface nanotexture. This fact underlines the potential application of the proposed technique in the field of microfluidics, where polydimethylsiloxane is gaining popularity as structural material for microfluidic devices.

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Articles you may be interested in Molecular structure effects on dry etching behavior of Si-containing resists in oxygen plasmaThis work is focused on the plasma development of siloxanes investigated as model Si-containing photoresist components that show a promise for bilayer lithography at 157 nm and other Next Generation Lithography technologies. In such lithography, the image is developed in the top photosensitive polymer and transferred to the ͑usually thick͒ organic underlayer by means of O 2 -based plasma etching. In this work particularly, the issue of line edge roughness ͑LER͒ induced by transfer etching and its reduction by means of plasma processing optimization is addressed. The experimental results reveal that low values of line-edge roughness are obtained in a high-density plasma reactor, if an F-but not O-containing etching first step is used in appropriate plasma conditions. The effect of different etching chemistries and processing conditions on imaging layer roughness formation is demonstrated with the aid of scanning electron microscopy images and image analysis for quantifying LER, and atomic force microscopy ͑AFM͒ for measuring surface roughness. X-ray photoelectron spectroscopy analysis of etched PDMS is used to show the evolution of the chemical modification of the PDMS layer, to measure the top oxide thickness, and to correlate both to processing conditions. In situ interferometry and ellipsometry are used to determine the etch resistance of the imaging PDMS layer and the selectivity of the transfer etching process. It is demonstrated that optimum LER correlates well with plasma processing conditions that ensure a nonselective first etching step prior to a highly selective main etching.

White light reflectance spectroscopy is applied to monitor vapor-induced thickness changes of polymer films, supported on suitable silicon substrates. Assuming unidirectional swelling due to the constraining support, the equilibrium volume swelling of four methacrylic polymers and two siloxane-based copolymers upon exposure to various activities of water, methanol, ethanol, and ethyl acetate vapor, at 30 C is evaluated. The deduced sorption isotherms were fitted to the Flory-Huggins equation and interaction parameters, as well as solubility coefficients at infinite solute dilution, were deduced for each binary system. The relative sorption capacity of the different classes of polymers toward the four vapors are in line with the expected solubility interactions between solvent and solute.