Anodic aluminum oxide nanoporous

An anodic aluminum oxide nanoporous membrane was used as a template for the synthesis of vertically aligned nanofibers of polyacrylonitrile (PAN) [57]. In a typical process, the precursor solution (18% PAN in DMF) was extruded through the template into a solidifying solution (a mixture of 40% DMF and 60% deionized water) where the precursor solution solidified. The template was then removed, and the solidified fibers washed with water and dried under air. Figure 9 shows SEM images of a surface formed by this technique that exhibits a WCA larger than 170°. 

Chekmenev, E.Y., Hu, J., Gor kov, P.L. et al. 2005. N and P solid-state NMR study of transmembrane domain alignment of M2 protein of influenza A virus in hydrated cylindrical lipid bilayers confined to anodic aluminum oxide nanopores. J. Magn. Reson. 173 322-327. 

The most commonly used hard templates are anodic aluminum oxide (AAO) and track-etched polycarbonate membranes, both of which are porous structured and commercially available. The pore size and thickness of the membranes can be well controlled, which then determine the dimension of the products templated by them. The pores in the AAO films prepared electrochemically from aluminum metals form a regular hexagonal array, with diameters of 200 nm commercially available. Smaller pore diameters down to 5 nm have also been reported (Martin 1995). Without external influences, capillary force is the main driving force for the Ti-precursor species to enter the pores of the templates. When the pore size is very small, electrochemical techniques have been employed to enhance the mass transfer into the nanopores (Limmer et al. 2002). 

Figure 7.8. Comparison of the resolution for (a) low-resolution SEMJ 5] with (b) high-resolution FESEMJI Both images are of a nanoporous anodized aluminum oxide template at identical magnification.

Another way to template thin films of nano-sized cylinders perpendicular to the surface is to start with a preformed membrane of track-etched polycarbonate or nanoporous alumina. A fiuid dispersion of a filler material can be drawn into the pores. Anodized aluminum oxide was the template for construction of lithium ion nanobatteries having many parallel cells filled with the solid state electrolyte PEO-LiOTf (poly(ethylene oxide)-lithium trifluoromethanesulfonate) and the electrodes coated on the top and bottom surfaces of the film (41). 

While the previously mentioned processes require complex instruments and high voltages up to 20 kV with limited scale, an alternative fabrication process is realized through a template wetting. Dissolved or molten PVDF is soaked into a nanoporous template (Fig. 5.7D) (Bhavanasi et al., 2014 Whiter et al., 2014). During the formation of nanowires, the PVDF is subjected to substantial stresses which result in preferential formation of a ferroelectric p-phase. Suitable templates include anodized aluminum oxide that is available commercially with a range of sizes, pore diameters, and pore densities. Furthermore, it is possible to free the nanowire from the template via a selective etch in phosphoric acid... 

The formation of nanostructured arrays of conjugated polymers by the utilization of nanoporous templates has been reported. The deposition of the polymer inside the pores can be achieved by filling the pores with a solution of polymer and evaporation of the solvent or by the direct synthesis of conjugated polymer inside the pores by chemical or electrochemical approaches. Porous templates were based on track-etched polycarbonate membranes [106-108] or alumina that is obtained by anodic aluminum oxidation (AAO) [109-lllj. Thus, periodic vertical channels with diameters between 20 and 120 nm are formed by first electrochemical oxidation and etching and then subsequent etching for pore widening (Figure 13.16). 

A novel one-sided NMR magnet has been developed for self-diffusion measurements in thin samples [7]. Using this technique, researchers have demonstrated measurements in bulk [BMIM][TFSI] and [BMIM][TFSI] confined in nanoporous anodized aluminum oxide membranes, as shown in Fig. 3. This operates at a proton Larmor frequency of 14.08 MFlz, and the expected appHcation is toward in situ measurements in portable energy devices. This method utilizes the fringe field to measure diffusion coefficients instead of conventional PFG-NMR. 

Cui L, Chen Y, Zhang G (2009) An optical fiber hydrogen sensor with Pd/Ag film. Optoelectron Lett 5 220-223 Ding D, Chen Z, Lu C (2006) Hydrogen sensing of nanoporous palladium films supported by anodic aluminum oxides. 

The first example of a high resolution solid-state 2D N PISEMA NMR spectrum has been reported for a transmembrane peptide aligned using hydrated cylindrical lipid bilayers formed inside nanoporous anodic aluminum oxide substrates. Using N and P NMR spectra, both the phospholipids and the protein transmembrane domain were shown to be uniformly aligned in the nanopores. 

Fig. 1.10 FESEM images of non-polar polymer nanotubes and nanowiies fabricated by using nanoporous Anodic Aluminum Oxide (AAO) template (Reprinted with permission from She et al. [149]. Copyright 2009 The Society of Polymer Science, Japan)...

FESEM. Both images are of a nanoporous anodized aluminum oxide template at identical magnification. 

An almost contonporary work to the previous report developed a unique yet simple method of BNNT synthesis with the assistance of nanoporous anodized aluminum oxide (AAO) template though the first template-assisted synthesis of BNNTs was reported earlier. In the former method, thermolysis of a boron precursor was used to generate the nanotubular structure inside the template that had been etched out later using hydrofluoric acid and repeated washing with water, methanol, and acetone. The process of incorporation of the polymer inside the nanochannels of the template is known as liquid-phase infiltration (LPI) technique, which has been successfully improvised to make nanotubes of almost 60 pm length and 200 nm diameter (Figure 20.10). 

Quasi-ID Nanostructures. A porous membrane with cylindrical pore geometry can be used as a template for the synthesis of quasi-ID nanostruetures, which was pioneered by Martin. Anodic aluminum oxide (AAO) films can be produced upon by anodie oxidation of aluminum foil in an eleetrolyte, typically of sulfuric, phosphoric, chromic, or oxalic acids. The AAO film contains hexagonally packed nanopores, perpendicular to the AAO membrane surface, uniform in diameter. Using them as template, highly ordered and vertically aligned nanowire arrays can be electrochemical produced. 

Inorganic templates, such as anodized aluminum oxide (AAO) can be prepared with tailored nanopores and can be used to infiltrate polymers [190-204],... 

Anodization of Al-Ti alloys with a Ti concentration in the range of 1 -35 % has been performed to fabricate a composite nanoporous oxide. An increase of the Ti content is found to enlarge few times the size of pores. Composite oxide films with the weight fraction of the titanium oxide exciding that of the aluminum oxide have been formed for the first time. The new nanostructured material has properties as alumina (AI2O3) as well as titanium oxide. 

Anodization techniques. Anodization has also been employed to fabricate 3-D nanoporous or nanotubular scaffolds of anodic titanium oxide and aluminum oxide [42,43]. These techniques are essentially the same as the anodization methods introduced in Chapter 2 and, thus, are not expanded upon here. 

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