Abstract: Organically modified silicate (ormosil) sol-gel thin films have many advantages over their inorganic sol-gel and polymeric counterparts for sensing applications. The addition of methyltrimethoxysilane (MTMS) to tetraethyl orthosilicate (TEOS)-based gels creates a film with much greater hydrophobicity and less cracking due to replacement of hydroxyl groups by non-hydrolyzable methyl groups. The more hydrophobic thin film is advantageous in oxygen sensing applications, since it allows only gaseous interaction with the sensing element, and liquid infiltration into the gel is minimized. Organic modification of the gels is found to increase the degree of fluorescence quenching in dip-coated films, as evidenced by fluorescence lifetime measurements, due to the more open structure of the ormosil. However, hydrophilicity can still be obtained in the ormosil thin films by adding smaller amounts of MTMS and greater amounts of TEOS. This creates a partially hydrophilic film which still maintains a low degree of cracking due to the MTMS addition. Hydrophilic films are much desired in hydrogen sulfide and carbon dioxide sensing applications, where liquid interaction with the gel matrix itself is necessary for proper protonation and deprotonation reactions. While TEOS-based spin-coated thin films have been shown to quench more poorly with additions of MTMS, it is found that low levels of organic modification will prevent cracking of the spun films while still maintaining a very high degree of fluorescence quenching. Hence, ormosil thin films have strong potential in a wide array of chemical, biochemical, and environmental sensing applications. !31
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