Production, Characterization, and Utilization of Aerosol-Deposited Sol - Gel-Derived Films

A new aerosol-based deposition method, for the production of sol - gel-derived films under ambient conditions, has been developed. Tetraethyl orthosilicate (TEOS) and N-octyltriethoxysilane (TrEOS-C₈)-derived sol - gel-processed films were produced using the new technique and compared to films produced by a conventional spin-casting approach. All films were characterized using scanning electron microscopy, profilometry, electron spectroscopy for chemical analysis (ESCA), diffuse-reflectance infrared Fourier transform spectroscopy, and steady-state fluorescence spectroscopy. Sol - gel-derived films produced using the aerosol-based method were uniform, and their thickness could be controlled between 0.6 and at least 3.0 μm. Spin casting of the neat sol - gel-processed solutions generally yielded more thick (2.0 ± 0.10 μm) films, but these thicker films were of poorer optical quality and very often more highly cracked. ESCA data demonstrate surface segregation of the C₈ moiety within the TrEOS - C₈-derived films. This segregation phenomenon is much more pronounced in the aerosol-generated films. A scenario is proposed where the distribution of and/or the dynamics/solvation of the C₈ residue within the aerosol droplet vs the bulk cast film are very different and lead to the segregation. Static fluorescence experiments demonstrate that several dopant classes can be incorporated directly into the sol - gel-processed solution and aerosol deposited. All results are also consistent with films that are heterogeneous on a molecular level. The utility of aerosol-deposited, sol - gel-derived films as a chemical sensing platform is demonstrated using fluorescence quenching of entrapped pyrene by O₂.