While super-hydrophobic materials have been thoroughly studied these last decades, few researches were carried out toward the elaboration of hydrophilic materials despite their high interest in various applications. For example, hydrophilic surfaces were proved to prevent surface fogging, limit bio-fouling or to enhance lubricity of materials. In this work, a bottom-up approach was undertaken to prepare hybrid hydrophilic materials. Sol-gel chemistry was selected since it enables a large choice of composition and structure (variety of precursors, methods of deposition) and can be carried out in mild conditions enabling the incorporation of organic components.
Specific hydrophilic compounds were tailored in order to be covalently linked to the sol-gel network and avoid their release over time. Polyethylene glycols (PEG) are non-toxic, bio-compatible and highly hydrophilic and were in this aim functionalized with alkoxysilane moeities using the hydrosilylation reaction. These functionalities can react according to hydrolysis-condensation mechanism and thus, PEG bis-functionalized can form hybrid sol-gel matrices in the right synthetic conditions. Swelling and mechanical properties could be easily adjusted thanks to the large variety of molecular weight available for PEG molecules and by modifying the PEG/silica ratio. Humidity-responsive swelling properties were highlighted from these gels, also exhibiting high stability over time and shape-memory.
In order to enhance even more the hydrophilic character of these materials, a new molecule bearing sulfonic acid groups was synthesized by telomerisation of 3-sulfopropyl acrylate potassium salt using as transfer agent the mercaptopropyltriethoxysilane. This highly hydrophilic precursor was mixed with the previous PEG bis-silane and the solution was deposited by dip-coating. The resulting coatings presented a good optical quality with a transmittance similar to glass while contact angle measurements showed higher hydrophilicity. Besides, it was showed that the incorporation of such compounds clearly enhance the anti-fogging properties since the coatings remain transparent after anti-warm and anti-cold fog tests. Based on these different results, it was demonstrated that this new design of hybrid sol-gel coatings is promising for any applications requesting a strong affinity to water.
 Bouvet-Marchand A. et al., ACS MAcro Lett., Submitted.