Interfacial behaviour of cubic silsesquioxane and silica nanoparticles in Langmuir and Langmuir-Blodgett films

In recent years fluorinated polyhedral oligomeric silsesquioxanes (POSS) have been established as useful for the fabrication of superhydrophobic surfaces, however little attention has been paid to their use for making ultrathin coatings by the Langmuir-Blodgett method. On the other hand, recently POSS compounds have been recognized as a new group of film-forming materials. In this study the interfacial behavior of fluorinated polyhedral oligomeric silsesquioxanes (POSS) mixed with silica nanoparticles was studied at the air/water interface. Surface pressure-area isotherms and Brewster angle microscopy revealed the formation of a mixed film. Incorporation of nanoparticles in a POSS monolayer caused formation or more condensed and rigid film as shown by analysis of compressibility and dilatational viscoelasticity. On the other hand POSS molecules act as an excellent dispersant which prevents silica nanoparticles from aggregation. Deposition of the Langmuir-Blodgett film composed of POSS and silica nanoparticles allowed a hydrophobic surface showing water contact angles reaching 135 degrees to be obtained, which suggests possible application of our approach in the fabrication of ultrathin, water-repellent coatings.