  Vegetable oil based hybrid films were developed thanks to a novel solvent-
and heating- free method at the air-water interface using silylated castor oil
cross-linked via a sol-gel reaction. To understand the mechanism of the hybrid
film formation, the reaction kinetics was studied in detail by using
complementary techniques: rheology, thermogravimetric analysis, and infrared
spectroscopy. The mechanical properties of the final films were investigated by
nano-indentation, whereas their structure was studied using a combination of
wide-angle X-ray scattering, electron diffraction, and atomic force microscopy.
We found that solid and transparent films form in 24 hours and, by changing the
silica precursor to castor oil ratio, their mechanical properties are tunable
in the MPa-range by about a factor of twenty. In addition to that, a possible
optimization of the cross-linking reaction with different catalysts was
explored and finally, cytotoxicity tests were performed on fibroblasts proving
the absence of film toxicity. The results of this work pave the way to a
straightforward synthesis of castor-oil films with tunable mechanical
properties: hybrid films cross-linked at the air-water interface combine an
easy and cheap spreading protocol with the features of their thermal history
optimized for possible future micro/nano drug loading, thus representing
excellent candidates for the replacement of non-environment friendly
petroleum-based materials.
