| Abstract
| - The tailoring of porous silica thin films synthesized using perfluoroalkylpyridinium chloride surfactants astemplating agents is achieved as a function of carbon dioxide processing conditions and surfactant tail lengthand branching. Well-ordered films with 2D hexagonal close-packed pore structure are obtained from sol−gelsynthesis using the following cationic fluorinated surfactants as templates: 1-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl)pyridinium chloride (HFOPC), 1-(3,3,4,4,5,5,6,6,7,8,8,8-dodecafluoro-7-trifluoromethyl-octyl)pyridinium chloride (HFDoMePC), and 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-decyl)pyridinium chloride (HFDePC). Processing the sol−gel film with CO2 (69−172 bar, 25 and 45 °C) immediatelyafter coating results in significant increases in pore diameter relative to the unprocessed thin films (increasingfrom 20% to 80% depending on surfactant template and processing conditions). Pore expansion increaseswith CO2 processing pressure, surfactant tail length, and surfactant branching. The varying degree of CO2induced expansion is attributed to the solvation of the “CO2-philic” fluorinated tail and is interpreted frominterfacial behavior of HFOPC, HFDoMePC, and HFDePC at the CO2−water interface.
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