The New Silica Vesicles Material Self-assembly And Structural Control

Novel porous materials have attracted much attention because of their significant applications in controlled release,catalyst supports,and separation.Generally,porous materials are fabricated by template approach.Surfactants can form different supra-molecular structures,such as vesicles and different liquid crystals.By using liquid crystal templating(LCT) or cooperative self-assembly,ordered mesoporous materials have been successfully synthesized.On the other hand,Hubert firstly reported the synthesis of unilamellar silica vesicles by directly coating the pre-formed unilamellar vesicles of ionic surfactants.Recently,by employing commercial triblock copolymer P123(EO₂₀PO₇₀EO₂₀,where EO is poly(ethylene oxide) and PO represents poly(propylene oxide)) as a template in the absence of organic cosolvents, unilamellar siliceous vesicles and nanofoams with large pore diameters and high pore volumes have been successfully synthesized.It is proposed that the siliceous vesicles are synthesized via a cooperative vesicle templating(CVT) approach.However, compared to thousands of documents on the study of ordered mesostructured materials via LCT approach,the general concept of fabricating vesicular materials possessing large pore diameters using CVT approach should be further investigated.In this thesis,we have systematically investigated the cooperative self-assembly of organic-inorganic vesicular structures from both the organic and inorganic parts.It is believed that the CVT mechanism can be generally applied to other systems. Moreover,through manipulating the LCT and CVT approaches,novel inorganic materials with various morphologies and hierarchical pore structures can be obtained.Firstly,we demonstrate that the vesicular or meso-structured inorganic-organic composites can be obtained selectively by just changing the silica source in one templating system.For triblock copolymers B50-6600(EO₃₉BO₄₇EO₃₉,where BO is poly(butylene oxide) either P85(EO₂₆PO₃₉EO₂₆) in a near neutral solution,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 utilization of tetraethyl orthosilicate(TEOS) leads to vesicles or foams.And we utilized ATR-FTIR technology as an "in-situ" tool to monitor the hydrolysis and condensation of TMOS or TEOS in the B50-6600 templating system.On the basis of the study,we propose a "differentiating effect" in our synthesis approach to understand the influence of different silica source.Moreover,by varying the ratios of mixed block copolymers with different hydrophilic/hydrophobic moieties and/or mixed silica sources or changing the molar ratios of silica precursors and surfactant, siliceous vesicular structures with controlled shapes(such as hollow spheres,hollow tubes),sizes(25-100 nm) and wall thickness(5-25 nm) have been successfully fabricated for the first time.When triblock copolymer B50-6600 with a large hydrophobic block and molecule weight is used as a template,by carefully adjusting the reaction conditions where both inorganic-organic composite vesicles and micelles are formed simultaneously in the solution,novel hierarchical siliceous hollow spheres(HSHS) materials with morphology similar to that of the raspberry has been obtained.Through studying the influence of reaction time and ionic strength on the self-assembled structure,we proposed a colloidal interaction model to understand the formation of HSHS structure.Commercial Pluronic triblock copolymer P123 is employed as a surfactant and Na₂SiO₃·9H2O as a silica source to synthesize siliceous materials at mild pH condition.By simply adjusting the reaction temperature and/or the concentrations of reactants,aggregated multilamellar vesicles,unilamellar nano-foams with a elliptical morphology,and labyrinth-like multilamellar vesicles with sponge-like walls have been successfully synthesized via a bioinspired approach.