This research involves the fabrication of encapsulated air-channels via acid-catalyzed degradation of photosensitive polycarbonates (PCs). There is a need for lower-temperature, degradable polymeric materials to fabricate buried air-channels for microelectromechanical systems (MEMS), microfluidic devices, and micro-reactors. Some polycarbonates undergo thermolytic degradation in the temperature range of 200 to 350 C. These polycarbonates are also known to undergo acid-catalyzed decomposition in the presence of catalytic amounts of acid. A small percentage of an acid in the polycarbonate formulation can greatly reduce the onset of decomposition temperature to the 100 to 180 C temperature range. The photoacid and thermalacid induced degradation behavior of PCs and its use as a sacrificial material for the formation of air-gaps have been studied in this work. The decomposition of several polycarbonates with the aid of in situ generated photo-acid has been demonstrated and applied to the fabrication of micro air-channels. Based on FT-IR, mass spectrometry, and thermogravimetric analysis (TGA), a degradation mechanism was proposed.[849]

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Recently, a method for fabricating air channels using a photodefinable sacrificial material (Unity 2203P) with acid-catalyzed degradation at low temperature was reported [J. P. Jayachandran et al. J Microelectromech. Syst. 12, 147 (2003)]. The acid is created via a ‘photoacid’ generator (PAG) either photolytically (when exposed to UV irradiation) or thermolytically (when heated to the decomposition temperature of the PAG). This approach to the fabrication of micro air-channel structures using low-temperature decomposable sacrificial materials has applications to air-gap formation for electrical/optical interconnects, microelectromechanical systems, microfluidics, and microreactors. In this study, the surface characteristics of the silica surface after the decomposition of Unity 2203P was explored. It was found that the surface inside the air-channel after low-temperature Unity 2203P decomposition was hydrophilic and was then converted to hydrophobic after higher-temperature treatment. The modification of the silicon surface using silane-based chemistries and a method for creating alternating hydrophobic/hydrophilic textures within a buried air channel has been demonstrated. Trifluoropropyl dimethylchlorosilane was the most effective surface treatment for creating hydrophobic channels. The hydrophobic/hydrophilic nature of the silicon surfaces is shown by the contact angle measurements and x-ray photoelectron spectroscopy analyses.

The first example of a phase-transfer-catalyzed alkylation reaction under supercritical fluid conditions is reported. The reaction is that of phenylacetonitrile and ethyl bromide in the presence of tetrabutylammonium bromide and potassium carbonate in supercritical ethane at 45, 60, and 75 °C and 138 bar. Results show that the reaction will go to completion in less than 24 h in the presence of the catalyst but that only a few percent conversion is achieved without it during the same period of time. The effects of catalyst concentration, temperature, and cosolvents are investigated. Catalyst solubility estimates and kinetic analyses suggest that the reaction takes place on the surface of the potassium carbonate particles. When the same reaction is attempted in supercritical carbon dioxide, both carboxylation and alkylation are observed. Cycloalkylation reactions between phenylacetonitrile and dibromoalkanes are also discussed.

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