Structuring and Functional Silica with Siloxane Copolymer (PDMS) Surfactants    

Many small triblock siloxane copolymers belonging to the family of poly(ethylene oxide)−poly(dimethylsiloxane)−poly-(ethylene oxide), PEO_x-PDMS_y-PEO_x, are now widely used as lubricants, water repellents, antifoaming and demulsification agents due to their amphiphilic properties.¹ This sort of triblock copolymers have also attracted much interest, especially for their resemblance to the Pluronic® copolymers already used as efficient template in the preparation of organized mesoporous silica materials.

The phase diagram of the triblock silicone copolymer (EO)₁₂−(DMS)₁₃−(EO)₁₂ (I) in water shows direct micellar and hexagonal phases, which are thermally stable. The structural parameters of the hexagonal liquid crystal were determined by SAXS and have been compared with those of micelles^{1, 2}.

Afterwards, mesoporous materials were synthesized through the self-assembling mechanism with this siloxane copolymer. The resulting molecular sieves are hexagonally ordered mesopores and  presented surprisingly perfect spherical morphology with homogeneous size distribution ². Then (EO)₁₂−(DMS)₁₃−(EO)₁₂ copolymer was  functionalized with triethoxysilane propyl isocyanate through the hydroxyl group carried by PEO side chains to afford (EtO₃Si-(CH₂)₃NHCOO-(EO)₁₂−(DMS)₁₃−(EO)₁₂ (F). The later was mixed to the genuine siloxane copolymer at variable ratios in order to obtain mesoporous silica materials with controllable surface chemistry. Thereby, we found astonishingly that the mesoporous particle morphology elongates from spheres to hexagonal rods relatively to the mixture ratio of silicon copolymer and functionalized compound. The morphology and the mesostructure of the mesoporous silica materials were characterized by electronic microscopy (TEM, SEM) and by SAXS.    

[1] Forny-Le Follotec, A.; Glatter, O.; Pezron, I.; Barré, L.; Noïk, C.; Dalmazzone, C.; Metlas-Komunjer, L., Macromolecules  2012, 45, 2874-2881.

[2] Stébé, M.J.; Emo, M.; Forny-Le Follotec, A.; Metlas-Komunjer, L.; Pezron, I.; Blin, J.L. Langmuir 2013, 29, 1618-1626. 

andreea.pasc@univ-lorraine.fr