Thermal Activation of Sol-Gel Hybrid Materials Films

Noam Ralbag, Hebrew university of Jerusalem, Jerusalem, Israel

The use of particles or films that can change their properties gradually is of a great interest, especially when tailor-made adaptation of a product is needed. Indeed, hybrid particles, built by entrapment of organic polymers in sol-gel matrixes, have already shown the ability to change their hydrophobic/hydrophilic nature by external control of the thermal activation [1].  In this study, an attempt has been made to expand this phenomenon to a 2D arrangement, by creating hybrid films with similar controllable properties triggered by thermal activation. The films made are hybrids of a hydrophobic organic polymer, polydimethylsiloxane (PDMS), entrapped within silica network, synthesized by the sol-gel process. The synthetic method is based on Stöber-like conditions along with organically modified silica dip-coating procedures. One of the key parameters for the successful synthesis is the choice of the surfactant that enables the polymer entrapment inside the silica network and allows the polymer to move inside the network when the thermal activation is induced. The films were deposited on two kinds of substrates: hydrophilic hydroxyl terminated substrates (such as activated glass) and hydrophobic substrate (surface modified with PDDA). We found that the nature of the substrate has an important role in determining the thermal behavior, affecting opposite trends in the change of the hydrophobicity/hydrophilicity nature. The films were fully characterized  by element mapping (EDX, XPS) and imaging (SEM) which proved the presence of the polymer inside the silica and the changes in the polymer distribution due to the thermal activation. Contact angle measurements showed the gradual change in the hydrophobicity of a water droplet on the film.

[1] Fuchs, I. and Avnir, D. (2013) Induction of amphiphilicity in polymer@silica particles: ceramic surfactants, Langmuir 29, 2835-2842