Unconventional silanization to create superhydrophobic substrates and their applications

Superhydrophobic coatings have been developed to warrant waterproof properties of synthetic materials for diverse applications, such as outdoor clothing, construction materials, and µPAD. Commonly, superhydrophobicity is achieved by increasing the surface roughness and lowering surface tension. Previously, substrates (paper, glass, and polymers) treated with dilute solutions of organosilanes have reached hydrophobicity. However, achieving superhydrophobicity via such conventional silanization reaction without fluorine-based precursors and complex fabrication procedures remains as a challenge. The first work presented is that off-the-shelf laboratory filter papers can be treated into superhydrophobic with a binary solution of short- and long-chain organosilanes. SEM studies confirmed that it is the thickness rather than pore size of the cellulose filter paper governing the superhydrophobicity. The modified filter paper is chemically stable and mechanically durable; it can readily be patterned with UV/ozone treatment to create hydrophilic regions for colorimetric assays of various analytes. Compared to conventional cellulose filter paper, glass microfiber filters are ideal for preparing quantitative fluorometric assays, owing to their extremely low fluorescence background. It was discovered that superhydrophobicity can be achieved on glass microfiber filters by reacting with MTS. Moreover, a fluorometric assay for quantitative copper detection based on "click chemistry" with a customized smartphone app was showcased on patterned glass microfiber filter substrates. This work augments the potential of superhydrophobic glass microfiber filters for multiplex fluorescent assays with ultralow background and high signal-to-noise ratio. The most remarkable finding in this thesis is the development of a protocol that OTS stoichiometrically hydrolyzes and condensates to micro-to-nanoscale hierarchical siloxane aggregates dispersible in industrial solvents. The coating exhibited superior performance in cost, scalability, robustness, and particularly the capability of encapsulating other functional materials. The unconventional silanization reactions to create superhydrophobic surfaces reported in this thesis are beyond the sole purpose of analytical chemistry research, and can be extended to develop marketable daily products with complete waterproofing properties.