Preparation Of Resistant Surfactant Self - Assembly And Ordered Mesoporous Materials

Amphiphilic surfactant, including small-molecule surfactant and amphiphilic block copolymers, exhibit the-unique property to self-assemble to various aggregations such as micelles, vesicles in solution. Stimulus responsive materials have gained attention benefiting from the ability to rapid response to the certain stimulus such as thermal, light and pH. They have been widely applied in various aspects of our lives such as controlled release、 chemocatalysis. Light possess special advantages over other stimulating sources such as remote control, accuracy operation, non-contact and so on. Multi-responsive systems were built up by combining more than one stimulus responsive groups. The development of these smart materials has aroused many attentions because they would possess more variable to be manipulated. More attention in the stimulus responsive materials made of the amphiphilic molecules is currently attracted to application on new fields such as the preparation of ordered mesoporous materials、nano/micro reactors.A novel triblock copolymer containing azobenzene (AZO) and N-isopropylacrylamide (NIPAM) was synthesized by atom transfer radical polymerization (ATRP) using a poly(ethylene oxide) bifunctional macroinitiator (Br-PEO-Br). The triblock copolymer was characterized by1H-NMR, gel permeation chromatography (GPC). Uniformly distributed polymeric micelles were obtained in aqueous solution by self-assembly method. Transmission electron microscope (TEM), fluorescence spectroscopy and dynamic light scattering (DLS) were used for the investigation of the self-assemblies and their stimuli-responsive behavior. Photoinduced release behavior was achieved with the as-prepared triblock copolymer micelles, which has not been observed in our previously-reported diblock copolymer micelles:the fluorescence intensity of Nile Red trapped in the triblock copolymer micelles dropped by approximately40%after UV and Vis light alternative irradiation, indicating that a portion of the Nile Red was released to the aqueous media. Besides, the micelles shrank during the heating process.As a model compound to investigate the application of responsive self-assembling materials on preparation of ordered mesoporous materials, a cationic azobenzene-derivated surfactant,6-(4’-ethoxy-4-azophenyl) hexyloxytrimethyl ammonium bromide (Me3A6AB2A) has been synthesized. Me3A6AB2A was used as the soft template for the preparation of mesostructured silica nanospheres by using tetraethylorthosilicate (TEOS) as the silica precursor in an alkaline aqueous solution. It was found the UV irradiation was helpful for the formation of uniform mesoporous silica nanospheres. Owing to the static electronic interaction between positively charged Me3A6AB2A and negatively charged silicate oligomers, Me3A6AB2A can assemble into rod-like micelles that further organize into radial mesostructured composite nanospheres with silicate. The azobenzene-derivated surfactants confined in the silica matrix were found to remain good photoresponsive property with alterable molecular size and polarity, and can be released rapidly from the silica framework using H2O/EtOH solution as the extraction solvent under the UV light irradiation. The mesoporous silica nanospheres after the removal of the template have highly open frameworks with accessible oriented mesopores, high surface area (381m2/g), uniform pore size (2.7nm) and uniform spherical diameter (-300nm). Through the mild extraction method, the released surfactants can be r.ecycled and reused as the template to prepare mesoporous silica nanospheres, which shows a green, environmentally friendly way to synthesize ordered mesoporous materials.