title: Self-assembly of designed oligomeric siloxanes with alkyl chains into silica-based hybrid mesostructures.
abstract: A novel self-assembly route to ordered silica-organic hybrids using well-defined siloxane oligomers with alkoxy functionality and covalently attached alkyl chains has been investigated. Various hybrid mesostructures were obtained by hydrolysis and polycondensation without the use of any structure-directing agents. The oligomers 1(Cn), having an alkylsilane core and three branched trimethoxysilyl groups, formed highly ordered lamellar phases when n = 14-18, while those with shorter alkyl chains formed cylindrical assemblies, slightly distorted two-dimensional (2D) hexagonal structures (n = 6-10), and a novel 2D monoclinic structure (n = 12). Furthermore, the mixtures of 1(Cn) with different chain lengths yielded well-ordered 2D hexagonal phases, possibly due to the better packing of the precursors. The hybrids consisting of cylindrical assemblies were converted to ordered porous silica with tunable pore sizes upon calcination to remove organic groups. The liquid-state 29Si NMR analysis of the hydrolysis and polycondensation processes of 1(Cn) revealed a unique intramolecular reaction yielding primarily the oligomer with a tetrasiloxane ring which is a new class of amphiphilic molecule having both self-assembling ability and high cross-linking ability. We also found that the mesostructure (lamellar or 2D hexagonal) was strictly controlled by varying the number of siloxane units per alkyl chain. These results provide a deeper understanding of the present self-assembly process that is strongly governed by the molecular packing of oligosiloxane precursors.
authors.affiliation: Department of Applied Chemistry, Waseda University, Ohkubo-3, Shinjuku-ku, Tokyo 169-8555, Japan. a-shimo@kurenai.waseda.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Shimojima
authors.forename: Zheng
authors.initials: Z
authors.lastname: Liu
authors.forename: Tetsu
authors.initials: T
authors.lastname: Ohsuna
authors.forename: Osamu
authors.initials: O
authors.lastname: Terasaki
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kuroda
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D008567:Membranes, Artificial; D015394:Molecular Structure; D049329:Nanostructures / Q000737:chemistry*; D010316:Particle Size; D012015:Reference Standards; D012822:Silicon Dioxide / Q000737:chemistry*; D012833:Siloxanes / Q000138:chemical synthesis* / Q000737:chemistry; D013499:Surface Properties
chemical_list: D008567:Membranes, Artificial; D012833:Siloxanes; D012822:Silicon Dioxide