Hydrogel Filled with Monodisperse Mesoporous Silica

Abstract

Mesoporous silica materials synthesized by condensation of silica species in the presence of structure directing templateshave been widely investigatedso far.The mesopores with precisely controllable size, ordering, topology, and very large surface area per weight are suitable for many applications such as adsorbent and catalyst supports. These materials would also serve as novel fillers for polymer materials; with addition of only small amount of the fillers, very effective physical interactions of the polymer chains on the pore surfaces as well as topological confinement of the polymer chains piercing through the mesopores are expected, which would allow significant enhancement in mechanical properties of the materials. In this study, we demonstrate the synthesis poly(N-isopropylacrylamide) gel doped with mesoporous silica particles (mMPS) that have very small size and narrow particle size distribution. The composite gel shows largely improved mechanical property. The mesoporous silica (MPS) particles were synthesized from an aqueous mixture of triethanolamine, cetyltrimethylammonium bromide, and tetraethoxysilene, according to the method reported in the literature1. The MPS colloid was added with monomer (N-isopropylacrylamide), chemicalcrosslinker (N,N'-methylenebisacrylamide) and photoinitiator (2-hydroxy-2-methylpropiophenon). The solution was sealed in a cell and irradiated with ultraviolet light to obtain composite gel by photopolymerization. In the transmission electron microscope images of the MPS, the particles with the diameter of around 20 nm were observed. The surface of the particles were not smooth but rough , indicating the presence of mesopores. Dynamic light scattering showed that the MPS have average diameter of MPS is 21.8 nm with the standard deviation of 5.3nm. The obtained gels were perfectly transparent, indicating no aggregation of the MPS in the gel. In the tensile stretching test, the gel doped with 0.0002 wt% showed the breaking strain of 305% and breaking stress of 36 kPa. These values are much better compared to the gel without MPS that showed the breaking strain of 56% and breaking stress of 11 kPa. It is notable that the elastic modulus of the gel is not so much different. The mechanical reinforcement is explained by thhe topological crosslink by the mesopores as well as physical crosslink by interaction between the polymer chains and the silica surface. Reference 1. Chihiro,U.et al. Chem. Commun. 2009, 5094.