Polymer-templated silica

Although typical FDU-1 silicas and other polymer-templated silicas with large cagelike mesopores tend to be significantly microporous, the FDU-1 sample calcined at 1000 °C appeared to be essentially free from microporosity, as can be inferred from the relation between its surface area, pore volume, and pore diameter. 

Richman EK et al (2008) Ordered mesoporous silicon through magnesium reduction of polymer templated silica thin films. Nano Lett 8(9) 3075-3079 Shen L et al (2012) Magnesiothermically reduced diatomaceous earth as a porous silicon anode material for lithium ion batteries. J Power Sources 213 229-232 Shen X et al (2013) Si/mesoporous carbon composite as an anode material for lithium ion batteries. J Alloys Compounds 552 60-64... 

Fang J, Kang CB, Huang Y, Tolbert SH, Pilon L (2012) Thermal conductivity of ordered mesoporous nanocrystalline silicon thin films made from magnesium reduction of polymer-templated silica. J Phys Chem C 116 12926-12933 Fricke J, Hummer E, Morper H-J, Scheuerpflug P (1989) Thermal properties of silica aerogels. Revue de Phys Appl Colloque C4 24 87-97... 

Another crucial problem is a proper account for the surface roughness and microporosity, which are inherent to a large number of novel polymer-templated silica and organosilica materials, such as, e.g. SBA-15 [11-14]. For many structures, especially those synthesized at low temperatures, the micropore volume cannot be reliably estimated from the comparison plot due to a competition between micropore filling and multilayer adsorption on the rough surface. 

We presented a novel quenched solid non-local density functional (QSNLDFT) model, which provides a r istic description of adsorption on amorphous surfaces without resorting to computationally expensive two- or three-dimensional DFT formulations. The main idea is to consider solid as a quenched component of the solid-fluid mixture rather than a source of the external potential. The QSNLDFT extends the quenched-annealed DFT proposed recently by M. Schmidt and cowoikers [23,24] for systems with hard core interactions to porous solids with attractive interactions. We presented several examples of calculated adsorption isotherms on amorphous and microporous solids, which are in qualitative agreement with experimental measurements on typical polymer-templated silica materials like SBA-15, FDU-1 and oftiers. Introduction of the solid density distribution in QSNLDFT eliminates strong layering of the fluid near the walls that was a characteristic feature of NLDFT models with smoodi pore walls. As the result, QSNLDFT predicts smooth isotherms in the region of polymolecular adsorption. The main advantage of the proposed approach is that QSNLDFT retains one-dimensional solid and fluid density distributions, and thus, provides computational efficiency and accuracy similar to conventional NLDFT models. 

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

Goltner, C. G Henke, S. Weissenberger, M. C. Antonietti, M. 1998. Mesoporous silica from lyotropic liquid crystal polymer templates. Angew. Chem. Int. Ed. 37 613-616. 

A scaled-up version of this central template-concentric sphere surface assembly approach has been demonstrated for the growth of multi-layer core-shell nano- and microparticles, based upon the repeated layer-by-layer deposition of linear polymers and silica nanoparticles onto a colloidal particle template (Figure 6.8) [60]. In this case, the regioselective chemistry occurs via electrostatic interactions, as opposed to the covalent bond formation of most of the examples in this chapter. The central colloidal seed particle dictates the final particle... 

The porous membrane templates described above do exhibit three-dimensionality, but with limited interconnectedness between the discrete tubelike structures. Porous structures with more integrated pore—solid architectures can be designed using templates assembled from discrete solid objects or su-pramolecular structures. One class of such structures are three-dimensionally ordered macroporous (or 3-DOM) solids, which are a class of inverse opal structures. The design of 3-DOM structures is based on the initial formation of a colloidal crystal composed of monodisperse polymer or silica spheres assembled in a close-packed arrangement. The interconnected void spaces of the template, 26 vol % for a face-centered-cubic array, are subsequently infiltrated with the desired material. 

Even though there is great interest in such systems based on polymers as supporting materials, this chapter essentially focuses on the use of minerals as support. The use of silica has been historically investigated, mainly for its large surface area. As mentioned later, micelle-templated silica (MTS) has recently been disclosed. 

In addition to recent advances in block co-polymer templating of periodic mesoporous silica and silica colloidal crystal templating of periodic mesopo-rous polymers [79], SAMs have been used for polymer patterning [80]. Mixtures of two strongly incompatible polymers, a polystyrene (PS)-polyvinylpyridine (PVP) blend, were found to phase separate when placed on a... 

Templates should be removed from the composites to yield porous structures. Polymer templates can be removed by calcination, by dissolution with appropriate solvents, or by photo degradation, while silicas are eliminated by dissolution in aqueous HF or NaOH solution. 

Ordered macroporous materials (OMMs) are a new family of porous materials that can be synthesized by using colloidal microspheies as the template. - The most unique characteristics of OMMs are their uniformly sized macropores arranged at micrometer length scale in three dimensions. Colloidal microspheres (latex polymer or silica) can self assemble into ordered arrays (synthetic opals) with a three-dimensional crystalline structure. The interstices in the colloidal crystals are infiltrated with a precursor material such as metal alkoxide. Upon removal of the template, a skeleton of the infiltrated material with a three-dimensionally ordered macroporous structure (inverse opals) is obtained. Because of the 30 periodicity of the materials, these structures have been extensively studied for photonic applications. In this paper, the synthesis and characterization of highly ordered macroporous materials with various compositions and functionalities (silica, organosilica, titana, titanosilicate, alumina) are presented. The application potential of OMMS in adsorption/separation is analyzed and discussed. 

A two-dimensional cylindrical confinement of spherical micelles formed by a copolymer inside a porous anodic aluminum oxide template leads to the formation of mesoporous Si02 nanorods. About 0.1 g of a block copolymer, polyethylene-co-butylene-block-polyethylene oxide (PHB-PEO), is dissolved in about 1 mL of ethanol with mild heating. The copolymer forms spherical micelles under this condition. To this about 0.5 g of tetraethyl orthosilicate (TEOS) and 0.25 g of HCl is added and the solution is stirred for 2 h. The porous anodic aluminum oxide templates are loaded now with a drop of the above precursor solution. After filling the template, the excess precursor solution containing the polymer and silica is wiped out. The template is aged at 25°C for about 24 h followed by calcination at 550°C. Finally, the template is removed with 5% H3PO4 at... 

Lettow, J.S. Han. Y.J. Schmidt-Winkel, P. Yang, P. Zhao, D. Stucky. G.D. Ying, J.Y. Hexagonal to mesocellular foam phase transition in polymer-templated mesoporous silicas. Langmuir 2000. 16. 8291. 

FIGURE 6.8 (a) Schematic illustration of the procedure for the synthesis of polymeric capsules based on surface-initiated RAFT polymerization using silica nanoparticles as templates, (b) TEM image of polymer grafted silica nanoparticles, (c) SEM and (d) TEM images of the synthesized polymeric capsules. Source Huang et al. [15]. Reproduced with permission of American Chemical Society. 

Table 14 Elution Volumes (IQ and Chromatographic Separation Factors (a j) for Substrates on Polymer-coated Silica Prepared using 48 as a Template...

Table 15 Capacity Factors k ) and Chromatographic Separation Factors ( y) for Imidazole and Substrates 48,50,52, and 53 on Polymer-coated Silicas Prepared using 48,50,52, or 53 as Templates...

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