Mesostructured natural rubber/in situ formed silica nanocomposites: A simple way to prepare mesoporous silica with hydrophobic properties

We report here a simple way to prepare mesoporous silica materials with hydrophobic properties, as natural rubber (NR)/hexagonal mesoporous silica (HMS) nanocomposites, via an in situ sol-gel process using tetraethyl orthosilicate (TEOS) and decylamine as a silica precursor and organic template, respectively. Effects of swelling the NR sheet in TEOS, prior to dissolution in tetrahydrofuran, on the mesostructure, chemical composition and hydrophobicity of the resulting nanocomposites were investigated. The NR/HMS prepared with the pre-swelling step had superior structural and textural properties to that prepared without the pre-swelling step. The presence of rubber phase entrapped in the mesostructured silica and genuinely mesostructured NR/silica nanocomposite framework was confirmed by osmium tetroxide staining coupled with transmission electron microscopy analysis. The results obtained from X-ray photoelectron spectroscopy indicated a good dispersion of NR molecules in the mesostructured nanocomposites, which was determined by the distribution of non-hydrolyzed ethoxy groups. The use of toluene extraction, followed by characterization of the resulting material, identified the weak nature of the NR-silica interaction. Dynamic light scattering indicated that the presence of TEOS in the pre-swollen NR matrix enhanced the diffusion of template molecules into the rubber phase, and the dispersion of NR molecules in the synthesis mixture. Finally, a plausible mechanism for the formation of NR/HMS nanocomposites via cooperative templating route, in which the remnant ethoxy groups acted as hydrophobic linkers between the rubber chains and the silica oligomers, was proposed.