Nanoparticles and nanostructured materials that are otherwise not accessible can be made by casting/replication of ordered mesoporous silica matrices. Pioneering work in the replication of inorganic host matrices with nanometer precision has been performed with carbon. Precursors were used to fill the channel system, followed by carbonization of the guest material and subsequent removal of the silica matrix.[1,2] Our own work in this direction was related to the polymerization of unconventional polymers and unusual morphologies. By using solutions of monomers andÐcontrary to the high-temperature treatment in carbonization processesÐmodest temperatures, we were, for instance, able to synthesize spherical high-temperature-resistant polyimide nanoparticles and polyimide nanoplates.
We report results of nitrogen and argon adsorption experiments performed at 77.4 and 87.3 K on novel micro/mesoporous silica materials with morphologically different networks of mesopores embedded into microporous matrixes: SE3030 silica with worm-like cylindrical channels of mode diameter of approximately 95 angstroms, KLE silica with cage-like spheroidal pores of ca. 140 angstroms, KLE/IL silica with spheroidal pores of approximately 140 angstroms connected by cylindrical channels of approximately 26 angstroms, and, also for a comparison, on Vycor glass with a disordered network of pores of mode diameter of approximately 70 angstroms. We show that the type of hysteresis loop formed by adsorption/desorption isotherms is determined by different mechanisms of condensation and evaporation and depends upon the shape and size of pores. We demonstrate that adsorption experiments performed with different adsorptives allow for detecting and separating the effects of pore blocking/percolation and cavitation in the course of evaporation. The results confirm that cavitation-controlled evaporation occurs in ink-bottle pores with the neck size smaller than a certain critical value. In this case, the pressure of evaporation does not depend upon the neck size. In pores with larger necks, percolation-controlled evaporation occurs, as observed for nitrogen (at 77.4 K) and argon (at 87.3 K) on porous Vycor glass. We elaborate a novel hybrid nonlocal density functional theory (NLDFT) method for calculations of pore size distributions from adsorption isotherms in the entire range of micro- and mesopores. The NLDFT method, applied to the adsorption branch of the isotherm, takes into account the effect of delayed capillary condensation in pores of different geometries. The pore size data obtained by the NLDFT method for SE3030, KLE, and KLE/IL silicas agree with the data of SANS/SAXS techniques.
Template pre-organized oligopeptides were conjugated to poly(ethylene oxide) chains yielding peptide-polymer-building blocks that self assemble into fiber-like nanostructures having a maximum length in the range of a micrometer.
Nanocasting, the three-dimensional transformation of selfassembled organic nanostructures into hollow inorganic replicas while preserving fine structural details, has recently turned out to be a versatile tool for the synthesis of porous media with new pore topologies. In the classical synthesis of mesoporous inorganic structures, [1,2] a route called ªsynergistic precipitationº, the order present in the starting material is not maintained in the product. Nanocasting, or the ªtrue lyotropic liquid-crystal approachº, [3±7] as introduced by Attard and Göltner, is different. Here, the starting high-concentration template phase is solidified by chemical-gelation reactions. In early work, it was shown that this technique offers the possibility of making a 1:1 imprint, or negative copy, of organic mesophases. X-ray scattering measurements performed throughout the process showed that the solidified hybrid inherits all the structural features of the original matrix. In order to enable nanocasting, the cast structure must be compatible with both the liquid-precursor phase as well as the final solidified replica. If this is not the case, the enormous interfaces involved (up to 1000 m 2 g ±1 ) will add up to unfavorable interface energies and the replication will break down. This is why most work is performed with sol±gel silica, [8] for which the surface chemistry is easy to address. Handling surface energies via poly(ethylene oxide) (PEO) tails, first demonstrated by Pinnavaia and co-workers, [9±11] is presumably the most frequently applied tool. Here, the formation of hydrogen bridges between the silicic acid framework and the ether oxygen atoms of the PEO chains stabilize the interface. The gelation of the SiO 2 network is preferentially performed at about pH 2, close to the isoelectric point of silicic acid. More recent work on the generation of mesoporous films of other crystalline inorganic materials by evaporation-induced self-assembly (EISA) [12] indicates that a second property of the templates severely influences the quality of the formed mesoporous films. This is the ªrobustnessº of the self-assembly process against processing conditions, such as temperature, alcohol content, or moisture level in the gaseous headspace.[13±15] Ozin and co-workers were able to produce mesoporous crystalline titania films on the basis of the commonly used pluronics poly(ethylene oxide)±poly(propylene oxide) block copolymers, but they relied on the specific replacement of ethanol by the more hydrophobic butanol in their recipes. [16,17] Already, the switch from the only moderately hydrophobic poly(propylene oxide) to the more hydrophobic poly(ethylene-co-butylene) significantly improved the process and allowed the generation of more complex mesoporous materials, such as titanium oxides [18] or even perovskites, [19] under a wider range of conditions and with improved structural quality. The scope of the present work is therefore to synthesize and explore the applicability of a template with extreme hydrophobic contrast, compos...
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