Silica films template removal

An example of the first approach is the integration of hydrogels into nanostructured silica films by addition of a suitable monomer (e.g., methyl methacrylate, /V-isopropyl acrylamide, etc.) and an initiator for radical polymerization to a solution containing a structure-directing surfactant and a prehydrolyzed silica precursor. During self-assembly, the monomers partition within the hydrophobic core of the surfactant mesophase postsynthesis polymerization (for instance, by UV treatment) followed by solvent washing to remove the surfactant template yields a polymer-silica nanohybrid. 

Burow and Minoura performed a similar kind of investigation to prepare protein imprinted polymers [48]. They used methacrylate modified silica particles as the carrier matrix on which imprinted sites were created. Using acrylic acid as the functional monomer and A,TV -1,2-diethylene bisacrylamide as the cross-linker, template polymerisation was carried out in the presence of glucose oxidase. This approach led to formation of a thin layer of cross-linked polymer film on the silica surface. After removing the template protein, substrate selectivity of the polymer was tested. Preferential affinity of the polymer for its template suggests the formation of substrate-selective binding sites in the polymer matrix. 

D and 3-D metal nanowire thin films[263] with tunable 3-10 nm wire diameters have been obtained by electrodeposition into mesoporous silica thin-film templates, resulting in nanowire arrays that reflect the pore structure of the template. Removal of silica is achieved via annealing followed by etching to leave mechanically strong freestanding metal nanowire films. 

Films are typically allowed to dry immediately after deposition to drive the silica condensation reaction toward completion. However, the film may not be fully condensed and stable after drying, and postsynthesis treatments are often employed to improve film stability, reduce shrinkage upon template removal, and drive the condensation reaction toward completion. 

Kim et al fabricated SWNT composite films with ordered voids by using sacrificial 2D silica colloidal template (Figure 6.7). Experimentally, SWNTs stabilized with water-soluble polythiophene were mixed with a suspension of silica colloidal particles, and then assembled into 2D colloid-SWNT array on flexible substrate. Selective removal of silica colloids led to a composite film... 

Using a similar TMOS/PTMOS/MTMOS system, Marx and Liron [24] templated thin silica films with propranolol. The films were spin-coated onto glass plates and the imprint removed via Soxhlet extraction with acidic methanol. Compared to a propranolol-imprinted acrylic polymer system, the sol-gel films showed lower capacity but better specificity and reproducibility. Additionally, they used radiolabeling experiments to demonstrate enantioselectivity in which the (5 )-propranolol-imprinted film was able to selectively bind 3H-(5 )-propranolol over nonradioactive (J )-propranolol, even when the (R) enantiomer was present in approximately 4000-fold excess. 

Hua Z.-L., Shi J.-L., Wang L., Zhang W.-H. Preparation of mesoporous silica films on a glass slide surfactant template removal by solvent extraction. J. Non-Cryst. Solids 2001 292 177-183... 

The synthesis of OMC involves the use of ordered mesoporous silica (OMS) template with a specific pore topology [7]. As illustrated in Figure 3.1, the appropriate carbon precursor (carbon sources such as sucrose, furfuryl alcohol, acetylene gas, pyrrole, and acrylonitrile) is fed into the pores of the template via the infiltration approach, followed by its carbonization to achieve the siUca-carbon composite and template removal in ethanol-water solution of HF or NaOH to obtain the mesoporous carbon replica. The structure of the as-obtained OMC strongly depends on the structure of the used template. Chang et al. [7] have reviewed the synthesis of OMC as support materials for fuel cell applications. The rod- and tube-type mesoporous carbon structures can be realized by filling carbon precursors in the template pores and coating carbon precursors as a thin film on the pore walls of the template, respectively. In order to get the well-defined structure of OMC, the template should have three-dimensional interconnected pore structure. On the other hand, the carbonization of the carbon precursors should be confined exclusively within the mesopores of the ordered mesoporous silica templates with sufficient carbon precursor filling therefore, before the pyrolysis process, the carbon soiu-ce should be converted to a cross-linked polymer induced by the use of the acid polymerization catalysts [5,7]. 

Imprinted metal oxide two-dimensional films have also been prepared using a CVD technique developed by Kodakari et al. [14,15]. They demonstrated that molecular imprints of aromatic aldehydes could be prepared in monolayer films of silica deposited by CVD on Sn02 surfaces. Taking advantage of the specific adsorption of aldehydes to Sn02, templates such as benzaldehyde were dispersed and bound to the surface, followed by tetramethoxysilane deposition. The templates were removed from the surface by gas phase reaction with ammonia, converting the aldehydes to nitriles. Gas phase binding studies performed on the calcined films of imprinted and non-imprinted systems showed that size selective memory for the benzaldehyde template existed. 

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