Soft template fabrication

Tanaka, S. Katayama, Y. Tate, M. R Hillhouse, H. W. Miyake, Y. 2007. Fabrication of continuous mesoporous carbon films with face-centered orthorhombic symmetry through a soft templating pathway. J. Mater. Chem. 17 3639-3645. 

The utilization of soft templates is helpful for the construction of rare earth hydroxide nanotubes. The s)mthesis of Y(OH)3 nanotubes could be assisted by PEG (Tang et al., 2003) or grafted with PMMA (Li et al., 2004 Mo et al., 2005). Hard templates like A AO are also studied for the fabrication of rare earth hydroxide nanowires (Bocchetta et al., 2007). 

On the other hand, the soft template method involves cooperative assembly between the structure-directing agents (usually surfactants) and organic precursor species in solution. Therefore, the carbon structures obtained via soft templating are more flexible and their formation is dependent on temperature, type of solvent and ionic strength. However, there are currently only limited examples for the successful fabrication of porous carbon via the soft template method, which were reviewed recently by Wan et alP Soft template and hard template routes have been classified as endotemplate and exotemplate, respectively. 

In addition to the above-mentioned soft templates, soup bubbles have been also used as templates to fabricate CPCs. PPy microcontainers with bowl-, cup-, and bottle-like morphologies have been electrochemically generated by direct oxidation of pyrrole in an aqueous solution of /3-naphthalenesulfonic acid (/3-NSA), first reported by Shi et al. [79-82]. The bubbles were produced by the decomposition of water. The gas bubbles and the aqueous solution containing the monomer and /3-NSA led to the formation of soap... 

As mentioned above, metal/CPs with core-sheath structure can be prepared by the template method. However, the approach based on the template technique is complicated and non-economical because of the need to remove the templates. In fact, metal/CPs with core-sheath structure can be fabricated via a one-step chemical polymerization [83-87]. Niu and co-workers demonstrated that Au/PANI coaxial nanocables could also be fabricated by the redox reaction between chloroauric acid and aniline in the presence of d-CSA [85]. In that case, CSA acted not only as a dopant, but also as a surfactant or a soft template. In addition to Ag/PPy and Au/PANI nanocables, cable-like Au/poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructures have been synthesized in the absence of any surfactant or stabilizer through one-step interfadal polymerization of EDOT dissolved in dichloromethane solvent and HAuCl dissolved in water [86]. Microscopy studies showed (Figure 13.6) that the outer and inner diameters of Au/PEDOT nanocables were aroimd 50 and 30 nm, respectively. 

Polymeric cylinders prepared via the self-assembly approach represent a versatile and powerful soft template for the fabrication of 1-D hybrid or inorganic nanomaterials with hierarchical architectures and complex functionaHties. 

Soft template method by using block copolymers was reported for first time by Liang et al. [72] in 2004. After that, a significant progress on the fabrication of carbon with a well ordered mesopores was achieved [32, 73-77]. Zhao and coworkers performed a widespread study of soft template via the triblock poly (ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems, PEO-PPO-PEO [65, 78]. Several ordered pore stmctures corresponding to various surfactant liquid crystal phases were synthesized by liquid crystal template pathway, a schematized synthesis procedure is shown in the Pig. 7.11. 

Next section covers extensive discussions of various fabrication methods for conducting polymer nanomaterials in detail. This section is divided by the soft template method, hard template method, and template-free method. 

In general, template method is classified by soft and hard templates. Whereas anodic aluminum oxide (AAO) membrane, track-etched polycarbonate (PC) and zeolite can be used as hard templates, soft templates include surfactant, cyclodextrin, liquid crystal, etc. Compared with soft and hard templates, template-free method represents the fabrication technique of conducting polymer nanomaterials without the template, which is discussed in this section [115]. 

Recently, soft template method has been used for the fabrication of various morphologies of polymer nanomaterials. There are several soft templates such as surfactant, liquid crystalline polymer, cyclo dextrin, and functionalized polymer [100,101,116-122]. Among them, surfactants, which imply cationic, anionic and non-ionic amphiphiles, are mostly used for the for-... 

Template-free techniques have been extensively studied for the fabrication of conducting polymer nanomaterials fabrication. Compared with hard and soft template methods, these methodologies provide a facile and practical route to produce pure, uniform, and high quality nanofibers. Template-free methods encompass various methods such as electrochemical synthesis, chemical polymerization, aqueous/organic interfacial polymerization, radi-olytic synthesis, and dispersion polymerization. 

Recently, a facile soft template synthesis was developed for fabricating PPy nanotubes against the hard template synthesis [153,249]. PPy nanotubes could be readily produced through a cylindrical micelle templating in re-... 

It is believed that this direct synthesis method (or soft template) will expand the possibility of synthesizing a variety of ordered porous carbon structures, facilitate their mass production, and lead to the fabrication of novel carbon and carbon-polymer porous materials. 

Microfabrication offers a way to produce homogeneous monodisperse particles that are not only spherical particles with controlled or asymmetrical shapes and architectures with a specific size can also be fabricated, which is not possible with the other methods. This method uses soft templates to produce monodisperse particles wherein the template can be fully dissolved in aqueous solutions once the particles are formed. There are many different methods of microfabrication particle replication in non wetting templates [72], microcontact hot printing [73], step and flash imprint lithography [74], and... 

Anisotropic particles, such as rods, are fabricated using two different methods. The first are solution based methods where a surfactant assembles soft templates in solution and promotes growth of particles in one direction" A variety of particles with extremely large aspect ratios can be produced with this method. An alternative method is to fabricate particles within the pores of a template (e.g. nanopore alumina or polycarbonate filters) that have well defined pore sizes Metal is deposited into the... 

Sodium bis(2-ethylhejQ l) sulfosuccinate (AOT), which can solubilize a relatively large amount of water [116], was selected as the sulfactant for the reverse microemulsion system. An aqueous FeCIa solution was added into an AOT/ apolar solvent mixture at room temperature. Subsequently, cylindrical reverse micelles, soft templates for the fabrication of nanotubular structures, were generated [117]. AOT micelles are generally a few nanometers in size in the absence of water. However, the addition of water dramatically increases the average aggregation number of the reverse micelles and thus the hydrod mamic radius of the aqueous micellar core increases [118]. 

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