Tuning cooperative vesicle templating and liquid crystal templating simply by varying silica source
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Chengzhong Yua) Department of Chemistry, and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Fudan University, Shanghai 200433, People’s Republic of China; and Australian Research Council (ARC) Centre of Excellence for Functional Nanomaterials, and Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia (Received 14 September 2009; accepted 29 December 2009)
The cooperative self-assembly of organic–inorganic siliceous composite structures has been studied from the aspect of inorganic precursors. We reveal that the vesicular or mesostructured materials can be obtained selectively by just changing the silica sources in one templating system. For poly(ethylene oxide)-type block copolymers with either poly (propylene oxide) or poly(butylene oxide) as the hydrophobic moieties, when the other synthesis parameters are exactly the same, the use of tetramethyl orthosilicate (TMOS) as a silica source gives rise to highly ordered mesostructures, while the use of tetraethyl orthosilicate (TEOS) leads to vesicles or foams. The attenuated total reflection Fourier transform infrared (ATR-FTIR) technique is used to monitor the silicate species derived from the hydrolysis and condensation of TMOS and TEOS as a function of the reaction time. On the basis of the ATR-FTIR results, we propose a “differentiating effect” at relatively high pH (4.7) to interpret the influence of different silica sources on the selforganized composite structures. For comparison, a “leveling effect” at relatively low pH (strong acidic conditions) is revealed to explain that both TMOS and TEOS lead to the same mesostructures. Our contribution provides a feasible and designable method to synthesize from conventional ordered mesostructures to novel vesicular structures, which are significant for their future practical applications. I. INTRODUCTION 1–4
5,6
Vesicles and liquid crystals are formed in different regions in the phase diagram of surfactants or block copolymers. A remarkable progress in material science is the synthesis of composite materials by using selfassembled supramolecular structures as the templates. By using liquid crystal templating (LCT)7,8 or cooperative self-assembly,9–11 ordered mesostructured organic– inorganic composites have been synthesized and this field has attracted thousands of documents until now.12,13 Hubert et al.14 first reported the synthesis of unilamellar silica vesicles by directly coating the preformed unilamellar vesicles of ionic surfactants. This method is obviously different from that of cooperatively self-assembled mesostructured materials.7,9 Recently, we proposed a cooperative vesicle templating (CVT) approach to synthesize siliceous unilamellar vesicles and foams by nonionic block copolymers,15–17 the syna)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0085
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J. Mater. Res., Vol. 25, No. 4, Apr 2010 Downloaded: 16 Mar 2015
thesis condition (pH
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