Mesoporous silicas with variable pore size and architecture were made by using aqueous solutions of block copolymers with one polyelectrolyte block as templates in a sol-gel process. Pore size and connectivity follow the structure of the block copolymer micelles or mesophases, i.e., the resulting silica gel network is a precise copy of the original self-assembly structure. In this paper, three cationic polybutadiene-b-poly(vinylpyridinium) block copolymers as well as an anionic poly(ethylethylene)-b-polystyrenesulfonate block are utilized as structure-directing media. Depending on the relative block lengths and the salt content in the reaction mixture, different aggregation structures are obtained, leading to well-defined spherical pores in the size range between 10 nm < ξ < 50 nm or more complex architectures, such as “rattles”, the casts of multilamellar vesicles. It is proposed that it is possible to use this precise silica casting procedure in order to depict and characterize unknown aggregation structures of block copolymers. Therefore silica casting appears to be a considerable alternative to the more tedious freeze-fracture preparations of similar colloidal systems.

Lyotropic phase morphologies of amphiphilic poly(butadiene-b-ethylene oxide) (PB-PEO) block copolymers are studied using transmission electron microscopy, small-angle X-ray scattering, smallangle neutron scattering, and polarized optical microscopy. The PB-PEO block copolymers form type-1 lyotropic phases comprising disordered micellar solutions (L1), spheres arranged on a bcc lattice (I1), hexagonally packed cylinders (H1), and lamellae (LR). Increasing molecular weight destabilizes the I1 and H1 phases and lowers the degree of order. For high molecular weight block copolymers the increase in chain conformational entropy leads to the formation of the sponge phase (L3). The transmission electron micrographs allow a detailed analysis of packing defects and epitaxial relations of the block copolymer lyotropic phases.

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This study reports the lyotropic phase behavior of two poly(ethylene oxide)-b-poly(butadiene) diblock copolymers and their cross-linking in the mesophase under retention of the mesoscopic order. The lyotropic phase behavior in water was characterized by polarized light microscopy and small-angle X-ray scattering (SAXS) in the concentration range from 0 to 100 wt % and in a temperature range between 20 and 100 °C. Depending on polymer composition and concentration micellar, hexagonal, lamellar, and cubic phases are found. Their ranges as well as pronounced coexisting phase regions were determined. Several of these mesophases were cross-linked via γ-irradiation to form mesostructured hydrogels. It is shown that the cross-linked polymer gel essentially maintains the parental lyotropic order, as proven by SAXS, polarized light microscopy, and transmission electron microscopy (TEM). TEM enables imaging of the polymer gel structure and thereby the visualization of the liquid-crystalline mesophase morphologies in themselves. The lyotropic mesophases as well as the lyotropic gels were used as templates for the synthesis of mesoporous silica, which is expected to give a negative solid copy of the ordered soft matter structure. The influence of the different templates on the silica structure formation is discussed.

The synthesis of mesoporous ceramic oxides with pore sizes between 2 and 50 nm is a recent trend in materials science. Most mesoporous silicas are prepared using ionic low molecular weight surfactants as structure-directing agents and sometimes inert oils as swelling additives.[1] This process, involving the precipitation of a surfactant-rich gel phase, is restricted to the synthesis of materials with pore sizes smaller than 8 nm, as the silica walls are too thin to support a larger-pore network. The use of bulk lyotropic liquid crystal phases of low molecular weight non-ionic surfactants [2±4] as templates partially solves the problem of mechanical stability. The wall thickness depends on the amount of inorganic precursor present in the preparation mixture, because the nanostructure is a result of directly casting the lyotropic bulk phase. However, surfactants are only available with restricted lengths of the hydrophobic chain, so that again the pore diameter is limited to approximately 4.5 nm.Casting the lyotropic phases of amphiphilic block copolymers (ABCs) is the method of choice for the synthesis of mechanically stable large-pore systems.[5] Here, the solidification of a siliceous precursor takes place in the aqueous domains of the microphase-separated medium, hence producing a monolithic cast of the original supramolecular aggregate. In addition, the ABC liquid crystal approach affords coherent porous coatings and macroscopic objects with continuous pore systems. [6] This approach was subsequently adopted by Chmelka et al., [7] who employed commercially available Pluronic-type triblock copolymers and obtained materials with pore diameters between 4.7 and 30 nm, and wall thicknesses between 3 and 5 nm. Their observations confirm the superiority of polymeric templates as porogens. [6] In this contribution, we present new non-ionic polymer templates with improved water-solubilities and a broader range of accessible molecular weights, which allows pore diameters of ceramic nanostructures to be extended beyond the known limits of this casting procedure. Templating the lyotropic aggregate structure of poly(butadiene-bethylene oxide) (PB-PEO) was studied over a wide range of block lengths, block length ratios and polymer concentration. The resulting silicas were characterized by transmission electron microscopy (TEM), porosimetry, and small-angle X-ray scattering (SAXS). The results demonstrate the great potential inherent in ABC templating as the method of choice for pore design in ceramic oxides. The polymers used in the experiments and their analytical data are summarized in Table 1. Table 1. Physical data of the amphiphilic block copolymers.[a] GPC measurement using CHCl 3 for the precursor PB (PB standard), the PEO block length is calculated from 1 H-NMR spectra (M n = number average molecular weight´10 3 kg/mol).[b] Repeat units.[c] Polydispersity, GPC in CHCl 3 , RI.The lyotropic phase behavior of the amphiphilic block copolymers in water was studied by polarized-light optical microscopy, as SAXS experime...